/* tfm.c
 *
 * Copyright (C) 2006-2014 wolfSSL Inc.
 *
 * This file is part of CyaSSL.
 *
 * CyaSSL is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * CyaSSL is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */


/*
 * Based on public domain TomsFastMath 0.10 by Tom St Denis, tomstdenis@iahu.ca,
 * http://math.libtomcrypt.com
 */

/**
 *  Edited by Moisés Guimarães (moisesguimaraesm@gmail.com)
 *  to fit CyaSSL's needs.
 */

#ifdef HAVE_CONFIG_H
    #include <config.h>
#endif

/* in case user set USE_FAST_MATH there */
#include <cyassl/ctaocrypt/settings.h>

#ifdef USE_FAST_MATH

#include <cyassl/ctaocrypt/tfm.h>
#include <ctaocrypt/src/asm.c>  /* will define asm MACROS or C ones */


/* math settings check */
word32 CheckRunTimeSettings(void)
{
    return CTC_SETTINGS;
}


/* math settings size check */
word32 CheckRunTimeFastMath(void)
{
    return FP_SIZE;
}


/* Functions */

void fp_add(fp_int *a, fp_int *b, fp_int *c)
{
  int     sa, sb;

  /* get sign of both inputs */
  sa = a->sign;
  sb = b->sign;

  /* handle two cases, not four */
  if (sa == sb) {
    /* both positive or both negative */
    /* add their magnitudes, copy the sign */
    c->sign = sa;
    s_fp_add (a, b, c);
  } else {
    /* one positive, the other negative */
    /* subtract the one with the greater magnitude from */
    /* the one of the lesser magnitude.  The result gets */
    /* the sign of the one with the greater magnitude. */
    if (fp_cmp_mag (a, b) == FP_LT) {
      c->sign = sb;
      s_fp_sub (b, a, c);
    } else {
      c->sign = sa;
      s_fp_sub (a, b, c);
    }
  }
}

/* unsigned addition */
void s_fp_add(fp_int *a, fp_int *b, fp_int *c)
{
  int      x, y, oldused;
  register fp_word  t;

  y       = MAX(a->used, b->used);
  oldused = MIN(c->used, FP_SIZE);   /* help static analysis w/ largest size */
  c->used = y;
 
  t = 0;
  for (x = 0; x < y; x++) {
      t         += ((fp_word)a->dp[x]) + ((fp_word)b->dp[x]);
      c->dp[x]   = (fp_digit)t;
      t        >>= DIGIT_BIT;
  }
  if (t != 0 && x < FP_SIZE) {
     c->dp[c->used++] = (fp_digit)t;
     ++x;
  }

  c->used = x;
  for (; x < oldused; x++) {
     c->dp[x] = 0;
  }
  fp_clamp(c);
}

/* c = a - b */
void fp_sub(fp_int *a, fp_int *b, fp_int *c)
{
  int     sa, sb;

  sa = a->sign;
  sb = b->sign;

  if (sa != sb) {
    /* subtract a negative from a positive, OR */
    /* subtract a positive from a negative. */
    /* In either case, ADD their magnitudes, */
    /* and use the sign of the first number. */
    c->sign = sa;
    s_fp_add (a, b, c);
  } else {
    /* subtract a positive from a positive, OR */
    /* subtract a negative from a negative. */
    /* First, take the difference between their */
    /* magnitudes, then... */
    if (fp_cmp_mag (a, b) != FP_LT) {
      /* Copy the sign from the first */
      c->sign = sa;
      /* The first has a larger or equal magnitude */
      s_fp_sub (a, b, c);
    } else {
      /* The result has the *opposite* sign from */
      /* the first number. */
      c->sign = (sa == FP_ZPOS) ? FP_NEG : FP_ZPOS;
      /* The second has a larger magnitude */
      s_fp_sub (b, a, c);
    }
  }
}

/* unsigned subtraction ||a|| >= ||b|| ALWAYS! */
void s_fp_sub(fp_int *a, fp_int *b, fp_int *c)
{
  int      x, oldbused, oldused;
  fp_word  t;

  oldused  = c->used;
  oldbused = b->used;
  c->used  = a->used;
  t       = 0;
  for (x = 0; x < oldbused; x++) {
     t         = ((fp_word)a->dp[x]) - (((fp_word)b->dp[x]) + t);
     c->dp[x]  = (fp_digit)t;
     t         = (t >> DIGIT_BIT)&1;
  }
  for (; x < a->used; x++) {
     t         = ((fp_word)a->dp[x]) - t;
     c->dp[x]  = (fp_digit)t;
     t         = (t >> DIGIT_BIT)&1;
   }
  for (; x < oldused; x++) {
     c->dp[x] = 0;
  }
  fp_clamp(c);
}

/* c = a * b */
void fp_mul(fp_int *A, fp_int *B, fp_int *C)
{
    int   y, yy;

    y  = MAX(A->used, B->used);
    yy = MIN(A->used, B->used);

    /* call generic if we're out of range */
    if (y + yy > FP_SIZE) {
       fp_mul_comba(A, B, C);
       return ;
    }

    /* pick a comba (unrolled 4/8/16/32 x or rolled) based on the size
       of the largest input.  We also want to avoid doing excess mults if the 
       inputs are not close to the next power of two.  That is, for example,
       if say y=17 then we would do (32-17)^2 = 225 unneeded multiplications 
    */

#ifdef TFM_MUL3
        if (y <= 3) {
           fp_mul_comba3(A,B,C);
           return;
        }
#endif
#ifdef TFM_MUL4
        if (y == 4) {
           fp_mul_comba4(A,B,C);
           return;
        }
#endif
#ifdef TFM_MUL6
        if (y <= 6) {
           fp_mul_comba6(A,B,C);
           return;
        }
#endif
#ifdef TFM_MUL7
        if (y == 7) {
           fp_mul_comba7(A,B,C);
           return;
        }
#endif
#ifdef TFM_MUL8
        if (y == 8) {
           fp_mul_comba8(A,B,C);
           return;
        }
#endif
#ifdef TFM_MUL9
        if (y == 9) {
           fp_mul_comba9(A,B,C);
           return;
        }
#endif
#ifdef TFM_MUL12
        if (y <= 12) {
           fp_mul_comba12(A,B,C);
           return;
        }
#endif
#ifdef TFM_MUL17
        if (y <= 17) {
           fp_mul_comba17(A,B,C);
           return;
        }
#endif

#ifdef TFM_SMALL_SET
        if (y <= 16) {
           fp_mul_comba_small(A,B,C);
           return;
        }
#endif        
#if defined(TFM_MUL20)
        if (y <= 20) {
           fp_mul_comba20(A,B,C);
           return;
        }
#endif
#if defined(TFM_MUL24)
        if (yy >= 16 && y <= 24) {
           fp_mul_comba24(A,B,C);
           return;
        }
#endif
#if defined(TFM_MUL28)
        if (yy >= 20 && y <= 28) {
           fp_mul_comba28(A,B,C);
           return;
        }
#endif
#if defined(TFM_MUL32)
        if (yy >= 24 && y <= 32) {
           fp_mul_comba32(A,B,C);
           return;
        }
#endif
#if defined(TFM_MUL48)
        if (yy >= 40 && y <= 48) {
           fp_mul_comba48(A,B,C);
           return;
        }
#endif        
#if defined(TFM_MUL64)
        if (yy >= 56 && y <= 64) {
           fp_mul_comba64(A,B,C);
           return;
        }
#endif
        fp_mul_comba(A,B,C);
}

void fp_mul_2(fp_int * a, fp_int * b)
{
  int     x, oldused;
   
  oldused = b->used;
  b->used = a->used;

  {
    register fp_digit r, rr, *tmpa, *tmpb;

    /* alias for source */
    tmpa = a->dp;
    
    /* alias for dest */
    tmpb = b->dp;

    /* carry */
    r = 0;
    for (x = 0; x < a->used; x++) {
    
      /* get what will be the *next* carry bit from the 
       * MSB of the current digit 
       */
      rr = *tmpa >> ((fp_digit)(DIGIT_BIT - 1));
      
      /* now shift up this digit, add in the carry [from the previous] */
      *tmpb++ = ((*tmpa++ << ((fp_digit)1)) | r);
      
      /* copy the carry that would be from the source 
       * digit into the next iteration 
       */
      r = rr;
    }

    /* new leading digit? */
    if (r != 0 && b->used != (FP_SIZE-1)) {
      /* add a MSB which is always 1 at this point */
      *tmpb = 1;
      ++(b->used);
    }

    /* now zero any excess digits on the destination 
     * that we didn't write to 
     */
    tmpb = b->dp + b->used;
    for (x = b->used; x < oldused; x++) {
      *tmpb++ = 0;
    }
  }
  b->sign = a->sign;
}

/* c = a * b */
void fp_mul_d(fp_int *a, fp_digit b, fp_int *c)
{
   fp_word  w;
   int      x, oldused;

   oldused = c->used;
   c->used = a->used;
   c->sign = a->sign;
   w       = 0;
   for (x = 0; x < a->used; x++) {
       w         = ((fp_word)a->dp[x]) * ((fp_word)b) + w;
       c->dp[x]  = (fp_digit)w;
       w         = w >> DIGIT_BIT;
   }
   if (w != 0 && (a->used != FP_SIZE)) {
      c->dp[c->used++] = (fp_digit) w;
      ++x;
   }
   for (; x < oldused; x++) {
      c->dp[x] = 0;
   }
   fp_clamp(c);
}

/* c = a * 2**d */
void fp_mul_2d(fp_int *a, int b, fp_int *c)
{
   fp_digit carry, carrytmp, shift;
   int x;

   /* copy it */
   fp_copy(a, c);

   /* handle whole digits */
   if (b >= DIGIT_BIT) {
      fp_lshd(c, b/DIGIT_BIT);
   }
   b %= DIGIT_BIT;

   /* shift the digits */
   if (b != 0) {
      carry = 0;   
      shift = DIGIT_BIT - b;
      for (x = 0; x < c->used; x++) {
          carrytmp = c->dp[x] >> shift;
          c->dp[x] = (c->dp[x] << b) + carry;
          carry = carrytmp;
      }
      /* store last carry if room */
      if (carry && x < FP_SIZE) {
         c->dp[c->used++] = carry;
      }
   }
   fp_clamp(c);
}

/* generic PxQ multiplier */
void fp_mul_comba(fp_int *A, fp_int *B, fp_int *C)
{
   int       ix, iy, iz, tx, ty, pa;
   fp_digit  c0, c1, c2, *tmpx, *tmpy;
   fp_int    tmp, *dst;

   COMBA_START;
   COMBA_CLEAR;
   
   /* get size of output and trim */
   pa = A->used + B->used;
   if (pa >= FP_SIZE) {
      pa = FP_SIZE-1;
   }

   if (A == C || B == C) {
      fp_zero(&tmp);
      dst = &tmp;
   } else {
      fp_zero(C);
      dst = C;
   }

   for (ix = 0; ix < pa; ix++) {
      /* get offsets into the two bignums */
      ty = MIN(ix, B->used-1);
      tx = ix - ty;

      /* setup temp aliases */
      tmpx = A->dp + tx;
      tmpy = B->dp + ty;

      /* this is the number of times the loop will iterrate, essentially its 
         while (tx++ < a->used && ty-- >= 0) { ... }
       */
      iy = MIN(A->used-tx, ty+1);

      /* execute loop */
      COMBA_FORWARD;
      for (iz = 0; iz < iy; ++iz) {
          /* TAO change COMBA_ADD back to MULADD */
          MULADD(*tmpx++, *tmpy--);
      }

      /* store term */
      COMBA_STORE(dst->dp[ix]);
  }
  COMBA_FINI;

  dst->used = pa;
  dst->sign = A->sign ^ B->sign;
  fp_clamp(dst);
  fp_copy(dst, C);
}

/* a/b => cb + d == a */
int fp_div(fp_int *a, fp_int *b, fp_int *c, fp_int *d)
{
  fp_int  q, x, y, t1, t2;
  int     n, t, i, norm, neg;

  /* is divisor zero ? */
  if (fp_iszero (b) == 1) {
    return FP_VAL;
  }

  /* if a < b then q=0, r = a */
  if (fp_cmp_mag (a, b) == FP_LT) {
    if (d != NULL) {
      fp_copy (a, d);
    } 
    if (c != NULL) {
      fp_zero (c);
    }
    return FP_OKAY;
  }

  fp_init(&q);
  q.used = a->used + 2;

  fp_init(&t1);
  fp_init(&t2);
  fp_init_copy(&x, a);
  fp_init_copy(&y, b);

  /* fix the sign */
  neg = (a->sign == b->sign) ? FP_ZPOS : FP_NEG;
  x.sign = y.sign = FP_ZPOS;

  /* normalize both x and y, ensure that y >= b/2, [b == 2**DIGIT_BIT] */
  norm = fp_count_bits(&y) % DIGIT_BIT;
  if (norm < (int)(DIGIT_BIT-1)) {
     norm = (DIGIT_BIT-1) - norm;
     fp_mul_2d (&x, norm, &x);
     fp_mul_2d (&y, norm, &y);
  } else {
     norm = 0;
  }

  /* note hac does 0 based, so if used==5 then its 0,1,2,3,4, e.g. use 4 */
  n = x.used - 1;
  t = y.used - 1;

  /* while (x >= y*b**n-t) do { q[n-t] += 1; x -= y*b**{n-t} } */
  fp_lshd (&y, n - t);                                             /* y = y*b**{n-t} */

  while (fp_cmp (&x, &y) != FP_LT) {
    ++(q.dp[n - t]);
    fp_sub (&x, &y, &x);
  }

  /* reset y by shifting it back down */
  fp_rshd (&y, n - t);

  /* step 3. for i from n down to (t + 1) */
  for (i = n; i >= (t + 1); i--) {
    if (i > x.used) {
      continue;
    }

    /* step 3.1 if xi == yt then set q{i-t-1} to b-1, 
     * otherwise set q{i-t-1} to (xi*b + x{i-1})/yt */
    if (x.dp[i] == y.dp[t]) {
      q.dp[i - t - 1] = (fp_digit) ((((fp_word)1) << DIGIT_BIT) - 1);
    } else {
      fp_word tmp;
      tmp = ((fp_word) x.dp[i]) << ((fp_word) DIGIT_BIT);
      tmp |= ((fp_word) x.dp[i - 1]);
      tmp /= ((fp_word)y.dp[t]);
      q.dp[i - t - 1] = (fp_digit) (tmp);
    }

    /* while (q{i-t-1} * (yt * b + y{t-1})) > 
             xi * b**2 + xi-1 * b + xi-2 
     
       do q{i-t-1} -= 1; 
    */
    q.dp[i - t - 1] = (q.dp[i - t - 1] + 1);
    do {
      q.dp[i - t - 1] = (q.dp[i - t - 1] - 1);

      /* find left hand */
      fp_zero (&t1);
      t1.dp[0] = (t - 1 < 0) ? 0 : y.dp[t - 1];
      t1.dp[1] = y.dp[t];
      t1.used = 2;
      fp_mul_d (&t1, q.dp[i - t - 1], &t1);

      /* find right hand */
      t2.dp[0] = (i - 2 < 0) ? 0 : x.dp[i - 2];
      t2.dp[1] = (i - 1 < 0) ? 0 : x.dp[i - 1];
      t2.dp[2] = x.dp[i];
      t2.used = 3;
    } while (fp_cmp_mag(&t1, &t2) == FP_GT);

    /* step 3.3 x = x - q{i-t-1} * y * b**{i-t-1} */
    fp_mul_d (&y, q.dp[i - t - 1], &t1);
    fp_lshd  (&t1, i - t - 1);
    fp_sub   (&x, &t1, &x);

    /* if x < 0 then { x = x + y*b**{i-t-1}; q{i-t-1} -= 1; } */
    if (x.sign == FP_NEG) {
      fp_copy (&y, &t1);
      fp_lshd (&t1, i - t - 1);
      fp_add (&x, &t1, &x);
      q.dp[i - t - 1] = q.dp[i - t - 1] - 1;
    }
  }

  /* now q is the quotient and x is the remainder 
   * [which we have to normalize] 
   */
  
  /* get sign before writing to c */
  x.sign = x.used == 0 ? FP_ZPOS : a->sign;

  if (c != NULL) {
    fp_clamp (&q);
    fp_copy (&q, c);
    c->sign = neg;
  }

  if (d != NULL) {
    fp_div_2d (&x, norm, &x, NULL);

/* the following is a kludge, essentially we were seeing the right remainder but 
   with excess digits that should have been zero
 */
    for (i = b->used; i < x.used; i++) {
        x.dp[i] = 0;
    }
    fp_clamp(&x);
    fp_copy (&x, d);
  }

  return FP_OKAY;
}

/* b = a/2 */
void fp_div_2(fp_int * a, fp_int * b)
{
  int     x, oldused;

  oldused = b->used;
  b->used = a->used;
  {
    register fp_digit r, rr, *tmpa, *tmpb;

    /* source alias */
    tmpa = a->dp + b->used - 1;

    /* dest alias */
    tmpb = b->dp + b->used - 1;

    /* carry */
    r = 0;
    for (x = b->used - 1; x >= 0; x--) {
      /* get the carry for the next iteration */
      rr = *tmpa & 1;

      /* shift the current digit, add in carry and store */
      *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));

      /* forward carry to next iteration */
      r = rr;
    }

    /* zero excess digits */
    tmpb = b->dp + b->used;
    for (x = b->used; x < oldused; x++) {
      *tmpb++ = 0;
    }
  }
  b->sign = a->sign;
  fp_clamp (b);
}

/* c = a / 2**b */
void fp_div_2d(fp_int *a, int b, fp_int *c, fp_int *d)
{
  int      D;
  fp_int   t;

  /* if the shift count is <= 0 then we do no work */
  if (b <= 0) {
    fp_copy (a, c);
    if (d != NULL) {
      fp_zero (d);
    }
    return;
  }

  fp_init(&t);

  /* get the remainder */
  if (d != NULL) {
    fp_mod_2d (a, b, &t);
  }

  /* copy */
  fp_copy(a, c);

  /* shift by as many digits in the bit count */
  if (b >= (int)DIGIT_BIT) {
    fp_rshd (c, b / DIGIT_BIT);
  }

  /* shift any bit count < DIGIT_BIT */
  D = (b % DIGIT_BIT);
  if (D != 0) {
    fp_rshb(c, D);
  }
  fp_clamp (c);
  if (d != NULL) {
    fp_copy (&t, d);
  }
}

/* c = a mod b, 0 <= c < b  */
int fp_mod(fp_int *a, fp_int *b, fp_int *c)
{
   fp_int t;
   int    err;

   fp_zero(&t);
   if ((err = fp_div(a, b, NULL, &t)) != FP_OKAY) {
      return err;
   }
   if (t.sign != b->sign) {
      fp_add(&t, b, c);
   } else {
      fp_copy(&t, c);
  }
  return FP_OKAY;
}

/* c = a mod 2**d */
void fp_mod_2d(fp_int *a, int b, fp_int *c)
{
   int x;

   /* zero if count less than or equal to zero */
   if (b <= 0) {
      fp_zero(c);
      return;
   }

   /* get copy of input */
   fp_copy(a, c);
 
   /* if 2**d is larger than we just return */
   if (b >= (DIGIT_BIT * a->used)) {
      return;
   }

  /* zero digits above the last digit of the modulus */
  for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
    c->dp[x] = 0;
  }
  /* clear the digit that is not completely outside/inside the modulus */
  c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) >> (DIGIT_BIT - b);
  fp_clamp (c);
}

static int fp_invmod_slow (fp_int * a, fp_int * b, fp_int * c)
{
  fp_int  x, y, u, v, A, B, C, D;
  int     res;

  /* b cannot be negative */
  if (b->sign == FP_NEG || fp_iszero(b) == 1) {
    return FP_VAL;
  }

  /* init temps */
  fp_init(&x);    fp_init(&y);
  fp_init(&u);    fp_init(&v);
  fp_init(&A);    fp_init(&B);
  fp_init(&C);    fp_init(&D);

  /* x = a, y = b */
  if ((res = fp_mod(a, b, &x)) != FP_OKAY) {
      return res;
  }
  fp_copy(b, &y);

  /* 2. [modified] if x,y are both even then return an error! */
  if (fp_iseven (&x) == 1 && fp_iseven (&y) == 1) {
    return FP_VAL;
  }

  /* 3. u=x, v=y, A=1, B=0, C=0,D=1 */
  fp_copy (&x, &u);
  fp_copy (&y, &v);
  fp_set (&A, 1);
  fp_set (&D, 1);

top:
  /* 4.  while u is even do */
  while (fp_iseven (&u) == 1) {
    /* 4.1 u = u/2 */
    fp_div_2 (&u, &u);

    /* 4.2 if A or B is odd then */
    if (fp_isodd (&A) == 1 || fp_isodd (&B) == 1) {
      /* A = (A+y)/2, B = (B-x)/2 */
      fp_add (&A, &y, &A);
      fp_sub (&B, &x, &B);
    }
    /* A = A/2, B = B/2 */
    fp_div_2 (&A, &A);
    fp_div_2 (&B, &B);
  }

  /* 5.  while v is even do */
  while (fp_iseven (&v) == 1) {
    /* 5.1 v = v/2 */
    fp_div_2 (&v, &v);

    /* 5.2 if C or D is odd then */
    if (fp_isodd (&C) == 1 || fp_isodd (&D) == 1) {
      /* C = (C+y)/2, D = (D-x)/2 */
      fp_add (&C, &y, &C);
      fp_sub (&D, &x, &D);
    }
    /* C = C/2, D = D/2 */
    fp_div_2 (&C, &C);
    fp_div_2 (&D, &D);
  }

  /* 6.  if u >= v then */
  if (fp_cmp (&u, &v) != FP_LT) {
    /* u = u - v, A = A - C, B = B - D */
    fp_sub (&u, &v, &u);
    fp_sub (&A, &C, &A);
    fp_sub (&B, &D, &B);
  } else {
    /* v - v - u, C = C - A, D = D - B */
    fp_sub (&v, &u, &v);
    fp_sub (&C, &A, &C);
    fp_sub (&D, &B, &D);
  }

  /* if not zero goto step 4 */
  if (fp_iszero (&u) == 0)
    goto top;

  /* now a = C, b = D, gcd == g*v */

  /* if v != 1 then there is no inverse */
  if (fp_cmp_d (&v, 1) != FP_EQ) {
    return FP_VAL;
  }

  /* if its too low */
  while (fp_cmp_d(&C, 0) == FP_LT) {
      fp_add(&C, b, &C);
  }
  
  /* too big */
  while (fp_cmp_mag(&C, b) != FP_LT) {
      fp_sub(&C, b, &C);
  }
  
  /* C is now the inverse */
  fp_copy(&C, c);
  return FP_OKAY;
}

/* c = 1/a (mod b) for odd b only */
int fp_invmod(fp_int *a, fp_int *b, fp_int *c)
{
  fp_int  x, y, u, v, B, D;
  int     neg;

  /* 2. [modified] b must be odd   */
  if (fp_iseven (b) == FP_YES) {
    return fp_invmod_slow(a,b,c);
  }

  /* init all our temps */
  fp_init(&x);  fp_init(&y);
  fp_init(&u);  fp_init(&v);
  fp_init(&B);  fp_init(&D);

  /* x == modulus, y == value to invert */
  fp_copy(b, &x);

  /* we need y = |a| */
  fp_abs(a, &y);

  /* 3. u=x, v=y, A=1, B=0, C=0,D=1 */
  fp_copy(&x, &u);
  fp_copy(&y, &v);
  fp_set (&D, 1);

top:
  /* 4.  while u is even do */
  while (fp_iseven (&u) == FP_YES) {
    /* 4.1 u = u/2 */
    fp_div_2 (&u, &u);

    /* 4.2 if B is odd then */
    if (fp_isodd (&B) == FP_YES) {
      fp_sub (&B, &x, &B);
    }
    /* B = B/2 */
    fp_div_2 (&B, &B);
  }

  /* 5.  while v is even do */
  while (fp_iseven (&v) == FP_YES) {
    /* 5.1 v = v/2 */
    fp_div_2 (&v, &v);

    /* 5.2 if D is odd then */
    if (fp_isodd (&D) == FP_YES) {
      /* D = (D-x)/2 */
      fp_sub (&D, &x, &D);
    }
    /* D = D/2 */
    fp_div_2 (&D, &D);
  }

  /* 6.  if u >= v then */
  if (fp_cmp (&u, &v) != FP_LT) {
    /* u = u - v, B = B - D */
    fp_sub (&u, &v, &u);
    fp_sub (&B, &D, &B);
  } else {
    /* v - v - u, D = D - B */
    fp_sub (&v, &u, &v);
    fp_sub (&D, &B, &D);
  }

  /* if not zero goto step 4 */
  if (fp_iszero (&u) == FP_NO) {
    goto top;
  }

  /* now a = C, b = D, gcd == g*v */

  /* if v != 1 then there is no inverse */
  if (fp_cmp_d (&v, 1) != FP_EQ) {
    return FP_VAL;
  }

  /* b is now the inverse */
  neg = a->sign;
  while (D.sign == FP_NEG) {
    fp_add (&D, b, &D);
  }
  fp_copy (&D, c);
  c->sign = neg;
  return FP_OKAY;
}

/* d = a * b (mod c) */
int fp_mulmod(fp_int *a, fp_int *b, fp_int *c, fp_int *d)
{
  fp_int tmp;
  fp_zero(&tmp);
  fp_mul(a, b, &tmp);
  return fp_mod(&tmp, c, d);
}

#ifdef TFM_TIMING_RESISTANT

/* timing resistant montgomery ladder based exptmod 

   Based on work by Marc Joye, Sung-Ming Yen, "The Montgomery Powering Ladder", Cryptographic Hardware and Embedded Systems, CHES 2002
*/
static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
{
  fp_int   R[2];
  fp_digit buf, mp;
  int      err, bitcnt, digidx, y;

  /* now setup montgomery  */
  if ((err = fp_montgomery_setup (P, &mp)) != FP_OKAY) {
     return err;
  }

  fp_init(&R[0]);   
  fp_init(&R[1]);   
   
  /* now we need R mod m */
  fp_montgomery_calc_normalization (&R[0], P);

  /* now set R[0][1] to G * R mod m */
  if (fp_cmp_mag(P, G) != FP_GT) {
     /* G > P so we reduce it first */
     fp_mod(G, P, &R[1]);
  } else {
     fp_copy(G, &R[1]);
  }
  fp_mulmod (&R[1], &R[0], P, &R[1]);

  /* for j = t-1 downto 0 do
        r_!k = R0*R1; r_k = r_k^2
  */
  
  /* set initial mode and bit cnt */
  bitcnt = 1;
  buf    = 0;
  digidx = X->used - 1;

  for (;;) {
    /* grab next digit as required */
    if (--bitcnt == 0) {
      /* if digidx == -1 we are out of digits so break */
      if (digidx == -1) {
        break;
      }
      /* read next digit and reset bitcnt */
      buf    = X->dp[digidx--];
      bitcnt = (int)DIGIT_BIT;
    }

    /* grab the next msb from the exponent */
    y     = (int)(buf >> (DIGIT_BIT - 1)) & 1;
    buf <<= (fp_digit)1;

    /* do ops */
    fp_mul(&R[0], &R[1], &R[y^1]); fp_montgomery_reduce(&R[y^1], P, mp);
    fp_sqr(&R[y], &R[y]);          fp_montgomery_reduce(&R[y], P, mp);
  }

   fp_montgomery_reduce(&R[0], P, mp);
   fp_copy(&R[0], Y);
   return FP_OKAY;
}   

#else

/* y = g**x (mod b) 
 * Some restrictions... x must be positive and < b
 */
static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
{
  fp_int   M[64], res;
  fp_digit buf, mp;
  int      err, bitbuf, bitcpy, bitcnt, mode, digidx, x, y, winsize;

  /* find window size */
  x = fp_count_bits (X);
  if (x <= 21) {
    winsize = 1;
  } else if (x <= 36) {
    winsize = 3;
  } else if (x <= 140) {
    winsize = 4;
  } else if (x <= 450) {
    winsize = 5;
  } else {
    winsize = 6;
  } 

  /* init M array */
  XMEMSET(M, 0, sizeof(M)); 

  /* now setup montgomery  */
  if ((err = fp_montgomery_setup (P, &mp)) != FP_OKAY) {
     return err;
  }

  /* setup result */
  fp_init(&res);

  /* create M table
   *
   * The M table contains powers of the input base, e.g. M[x] = G^x mod P
   *
   * The first half of the table is not computed though accept for M[0] and M[1]
   */

   /* now we need R mod m */
   fp_montgomery_calc_normalization (&res, P);

   /* now set M[1] to G * R mod m */
   if (fp_cmp_mag(P, G) != FP_GT) {
      /* G > P so we reduce it first */
      fp_mod(G, P, &M[1]);
   } else {
      fp_copy(G, &M[1]);
   }
   fp_mulmod (&M[1], &res, P, &M[1]);

  /* compute the value at M[1<<(winsize-1)] by squaring M[1] (winsize-1) times */
  fp_copy (&M[1], &M[1 << (winsize - 1)]);
  for (x = 0; x < (winsize - 1); x++) {
    fp_sqr (&M[1 << (winsize - 1)], &M[1 << (winsize - 1)]);
    fp_montgomery_reduce (&M[1 << (winsize - 1)], P, mp);
  }

  /* create upper table */
  for (x = (1 << (winsize - 1)) + 1; x < (1 << winsize); x++) {
    fp_mul(&M[x - 1], &M[1], &M[x]);
    fp_montgomery_reduce(&M[x], P, mp);
  }

  /* set initial mode and bit cnt */
  mode   = 0;
  bitcnt = 1;
  buf    = 0;
  digidx = X->used - 1;
  bitcpy = 0;
  bitbuf = 0;

  for (;;) {
    /* grab next digit as required */
    if (--bitcnt == 0) {
      /* if digidx == -1 we are out of digits so break */
      if (digidx == -1) {
        break;
      }
      /* read next digit and reset bitcnt */
      buf    = X->dp[digidx--];
      bitcnt = (int)DIGIT_BIT;
    }

    /* grab the next msb from the exponent */
    y     = (int)(buf >> (DIGIT_BIT - 1)) & 1;
    buf <<= (fp_digit)1;

    /* if the bit is zero and mode == 0 then we ignore it
     * These represent the leading zero bits before the first 1 bit
     * in the exponent.  Technically this opt is not required but it
     * does lower the # of trivial squaring/reductions used
     */
    if (mode == 0 && y == 0) {
      continue;
    }

    /* if the bit is zero and mode == 1 then we square */
    if (mode == 1 && y == 0) {
      fp_sqr(&res, &res);
      fp_montgomery_reduce(&res, P, mp);
      continue;
    }

    /* else we add it to the window */
    bitbuf |= (y << (winsize - ++bitcpy));
    mode    = 2;

    if (bitcpy == winsize) {
      /* ok window is filled so square as required and multiply  */
      /* square first */
      for (x = 0; x < winsize; x++) {
        fp_sqr(&res, &res);
        fp_montgomery_reduce(&res, P, mp);
      }

      /* then multiply */
      fp_mul(&res, &M[bitbuf], &res);
      fp_montgomery_reduce(&res, P, mp);

      /* empty window and reset */
      bitcpy = 0;
      bitbuf = 0;
      mode   = 1;
    }
  }

  /* if bits remain then square/multiply */
  if (mode == 2 && bitcpy > 0) {
    /* square then multiply if the bit is set */
    for (x = 0; x < bitcpy; x++) {
      fp_sqr(&res, &res);
      fp_montgomery_reduce(&res, P, mp);

      /* get next bit of the window */
      bitbuf <<= 1;
      if ((bitbuf & (1 << winsize)) != 0) {
        /* then multiply */
        fp_mul(&res, &M[1], &res);
        fp_montgomery_reduce(&res, P, mp);
      }
    }
  }

  /* fixup result if Montgomery reduction is used
   * recall that any value in a Montgomery system is
   * actually multiplied by R mod n.  So we have
   * to reduce one more time to cancel out the factor
   * of R.
   */
  fp_montgomery_reduce(&res, P, mp);

  /* swap res with Y */
  fp_copy (&res, Y);
  return FP_OKAY;
}

#endif

int fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
{
   /* prevent overflows */
   if (P->used > (FP_SIZE/2)) {
      return FP_VAL;
   }

   if (X->sign == FP_NEG) {
#ifndef POSITIVE_EXP_ONLY  /* reduce stack if assume no negatives */
      int    err;
      fp_int tmp;

      /* yes, copy G and invmod it */
      fp_copy(G, &tmp);
      if ((err = fp_invmod(&tmp, P, &tmp)) != FP_OKAY) {
         return err;
      }
      X->sign = FP_ZPOS;
      err =  _fp_exptmod(&tmp, X, P, Y);
      if (X != Y) {
         X->sign = FP_NEG;
      }
      return err;
#else
      return FP_VAL;
#endif 
   }
   else {
      /* Positive exponent so just exptmod */
      return _fp_exptmod(G, X, P, Y);
   }
}

/* computes a = 2**b */
void fp_2expt(fp_int *a, int b)
{
   int     z;

   /* zero a as per default */
   fp_zero (a);

   if (b < 0) { 
      return;
   }

   z = b / DIGIT_BIT;
   if (z >= FP_SIZE) {
      return; 
   }

  /* set the used count of where the bit will go */
  a->used = z + 1;

  /* put the single bit in its place */
  a->dp[z] = ((fp_digit)1) << (b % DIGIT_BIT);
}

/* b = a*a  */
void fp_sqr(fp_int *A, fp_int *B)
{
    int y = A->used;

    /* call generic if we're out of range */
    if (y + y > FP_SIZE) {
       fp_sqr_comba(A, B);
       return ;
    }

#if defined(TFM_SQR3)
        if (y <= 3) {
           fp_sqr_comba3(A,B);
           return;
        }
#endif
#if defined(TFM_SQR4)
        if (y == 4) {
           fp_sqr_comba4(A,B);
           return;
        }
#endif
#if defined(TFM_SQR6)
        if (y <= 6) {
           fp_sqr_comba6(A,B);
           return;
        }
#endif
#if defined(TFM_SQR7)
        if (y == 7) {
           fp_sqr_comba7(A,B);
           return;
        }
#endif
#if defined(TFM_SQR8)
        if (y == 8) {
           fp_sqr_comba8(A,B);
           return;
        }
#endif
#if defined(TFM_SQR9)
        if (y == 9) {
           fp_sqr_comba9(A,B);
           return;
        }
#endif
#if defined(TFM_SQR12)
        if (y <= 12) {
           fp_sqr_comba12(A,B);
           return;
        }
#endif
#if defined(TFM_SQR17)
        if (y <= 17) {
           fp_sqr_comba17(A,B);
           return;
        }
#endif
#if defined(TFM_SMALL_SET)
        if (y <= 16) {
           fp_sqr_comba_small(A,B);
           return;
        }
#endif
#if defined(TFM_SQR20)
        if (y <= 20) {
           fp_sqr_comba20(A,B);
           return;
        }
#endif
#if defined(TFM_SQR24)
        if (y <= 24) {
           fp_sqr_comba24(A,B);
           return;
        }
#endif
#if defined(TFM_SQR28)
        if (y <= 28) {
           fp_sqr_comba28(A,B);
           return;
        }
#endif
#if defined(TFM_SQR32)
        if (y <= 32) {
           fp_sqr_comba32(A,B);
           return;
        }
#endif
#if defined(TFM_SQR48)
        if (y <= 48) {
           fp_sqr_comba48(A,B);
           return;
        }
#endif
#if defined(TFM_SQR64)
        if (y <= 64) {
           fp_sqr_comba64(A,B);
           return;
        }
#endif
       fp_sqr_comba(A, B);
}

/* generic comba squarer */
void fp_sqr_comba(fp_int *A, fp_int *B)
{
  int       pa, ix, iz;
  fp_digit  c0, c1, c2;
  fp_int    tmp, *dst;
#ifdef TFM_ISO
  fp_word   tt;
#endif    

  /* get size of output and trim */
  pa = A->used + A->used;
  if (pa >= FP_SIZE) {
     pa = FP_SIZE-1;
  }

  /* number of output digits to produce */
  COMBA_START;
  COMBA_CLEAR;

  if (A == B) {
     fp_zero(&tmp);
     dst = &tmp;
  } else {
     fp_zero(B);
     dst = B;
  }

  for (ix = 0; ix < pa; ix++) { 
      int      tx, ty, iy;
      fp_digit *tmpy, *tmpx;

      /* get offsets into the two bignums */
      ty = MIN(A->used-1, ix);
      tx = ix - ty;

      /* setup temp aliases */
      tmpx = A->dp + tx;
      tmpy = A->dp + ty;

      /* this is the number of times the loop will iterrate,
         while (tx++ < a->used && ty-- >= 0) { ... }
       */
      iy = MIN(A->used-tx, ty+1);

      /* now for squaring tx can never equal ty 
       * we halve the distance since they approach 
       * at a rate of 2x and we have to round because 
       * odd cases need to be executed
       */
      iy = MIN(iy, (ty-tx+1)>>1);

      /* forward carries */
      COMBA_FORWARD;

      /* execute loop */
      for (iz = 0; iz < iy; iz++) {
          SQRADD2(*tmpx++, *tmpy--);
      }

      /* even columns have the square term in them */
      if ((ix&1) == 0) {
          /* TAO change COMBA_ADD back to SQRADD */
          SQRADD(A->dp[ix>>1], A->dp[ix>>1]);
      }

      /* store it */
      COMBA_STORE(dst->dp[ix]);
  }

  COMBA_FINI;

  /* setup dest */
  dst->used = pa;
  fp_clamp (dst);
  if (dst != B) {
     fp_copy(dst, B);
  }
}

int fp_cmp(fp_int *a, fp_int *b)
{
   if (a->sign == FP_NEG && b->sign == FP_ZPOS) {
      return FP_LT;
   } else if (a->sign == FP_ZPOS && b->sign == FP_NEG) {
      return FP_GT;
   } else {
      /* compare digits */
      if (a->sign == FP_NEG) {
         /* if negative compare opposite direction */
         return fp_cmp_mag(b, a);
      } else {
         return fp_cmp_mag(a, b);
      }
   }
}

/* compare against a single digit */
int fp_cmp_d(fp_int *a, fp_digit b)
{
  /* compare based on sign */
  if ((b && a->used == 0) || a->sign == FP_NEG) {
    return FP_LT;
  }

  /* compare based on magnitude */
  if (a->used > 1) {
    return FP_GT;
  }

  /* compare the only digit of a to b */
  if (a->dp[0] > b) {
    return FP_GT;
  } else if (a->dp[0] < b) {
    return FP_LT;
  } else {
    return FP_EQ;
  }

}

int fp_cmp_mag(fp_int *a, fp_int *b)
{
   int x;

   if (a->used > b->used) {
      return FP_GT;
   } else if (a->used < b->used) {
      return FP_LT;
   } else {
      for (x = a->used - 1; x >= 0; x--) {
          if (a->dp[x] > b->dp[x]) {
             return FP_GT;
          } else if (a->dp[x] < b->dp[x]) {
             return FP_LT;
          }
      }
   }
   return FP_EQ;
}

/* setups the montgomery reduction */
int fp_montgomery_setup(fp_int *a, fp_digit *rho)
{
  fp_digit x, b;

/* fast inversion mod 2**k
 *
 * Based on the fact that
 *
 * XA = 1 (mod 2**n)  =>  (X(2-XA)) A = 1 (mod 2**2n)
 *                    =>  2*X*A - X*X*A*A = 1
 *                    =>  2*(1) - (1)     = 1
 */
  b = a->dp[0];

  if ((b & 1) == 0) {
    return FP_VAL;
  }

  x = (((b + 2) & 4) << 1) + b; /* here x*a==1 mod 2**4 */
  x *= 2 - b * x;               /* here x*a==1 mod 2**8 */
  x *= 2 - b * x;               /* here x*a==1 mod 2**16 */
  x *= 2 - b * x;               /* here x*a==1 mod 2**32 */
#ifdef FP_64BIT
  x *= 2 - b * x;               /* here x*a==1 mod 2**64 */
#endif

  /* rho = -1/m mod b */
  *rho = (fp_digit) (((fp_word) 1 << ((fp_word) DIGIT_BIT)) - ((fp_word)x));

  return FP_OKAY;
}

/* computes a = B**n mod b without division or multiplication useful for
 * normalizing numbers in a Montgomery system.
 */
void fp_montgomery_calc_normalization(fp_int *a, fp_int *b)
{
  int     x, bits;

  /* how many bits of last digit does b use */
  bits = fp_count_bits (b) % DIGIT_BIT;
  if (!bits) bits = DIGIT_BIT;

  /* compute A = B^(n-1) * 2^(bits-1) */
  if (b->used > 1) {
     fp_2expt (a, (b->used - 1) * DIGIT_BIT + bits - 1);
  } else {
     fp_set(a, 1);
     bits = 1;
  }

  /* now compute C = A * B mod b */
  for (x = bits - 1; x < (int)DIGIT_BIT; x++) {
    fp_mul_2 (a, a);
    if (fp_cmp_mag (a, b) != FP_LT) {
      s_fp_sub (a, b, a);
    }
  }
}


#ifdef TFM_SMALL_MONT_SET
    #include "fp_mont_small.i"
#endif

/* computes x/R == x (mod N) via Montgomery Reduction */
void fp_montgomery_reduce(fp_int *a, fp_int *m, fp_digit mp)
{
   fp_digit c[FP_SIZE], *_c, *tmpm, mu = 0;
   int      oldused, x, y, pa;

   /* bail if too large */
   if (m->used > (FP_SIZE/2)) {
      (void)mu;                     /* shut up compiler */
      return;
   }

#ifdef TFM_SMALL_MONT_SET
   if (m->used <= 16) {
      fp_montgomery_reduce_small(a, m, mp);
      return;
   }
#endif


   /* now zero the buff */
   XMEMSET(c, 0, sizeof c);
   pa = m->used;

   /* copy the input */
   oldused = a->used;
   for (x = 0; x < oldused; x++) {
       c[x] = a->dp[x];
   }
   MONT_START;

   for (x = 0; x < pa; x++) {
       fp_digit cy = 0;
       /* get Mu for this round */
       LOOP_START;
       _c   = c + x;
       tmpm = m->dp;
       y = 0;
       #if (defined(TFM_SSE2) || defined(TFM_X86_64))
        for (; y < (pa & ~7); y += 8) {
              INNERMUL8;
              _c   += 8;
              tmpm += 8;
           }
       #endif

       for (; y < pa; y++) {
          INNERMUL;
          ++_c;
       }
       LOOP_END;
       while (cy) {
           PROPCARRY;
           ++_c;
       }
  }         

  /* now copy out */
  _c   = c + pa;
  tmpm = a->dp;
  for (x = 0; x < pa+1; x++) {
     *tmpm++ = *_c++;
  }

  for (; x < oldused; x++)   {
     *tmpm++ = 0;
  }

  MONT_FINI;

  a->used = pa+1;
  fp_clamp(a);
  
  /* if A >= m then A = A - m */
  if (fp_cmp_mag (a, m) != FP_LT) {
    s_fp_sub (a, m, a);
  }
}

void fp_read_unsigned_bin(fp_int *a, unsigned char *b, int c)
{
  /* zero the int */
  fp_zero (a);

  /* If we know the endianness of this architecture, and we're using
     32-bit fp_digits, we can optimize this */
#if (defined(LITTLE_ENDIAN_ORDER) || defined(BIG_ENDIAN_ORDER)) && defined(FP_32BIT)
  /* But not for both simultaneously */
#if defined(LITTLE_ENDIAN_ORDER) && defined(BIG_ENDIAN_ORDER)
#error Both LITTLE_ENDIAN_ORDER and BIG_ENDIAN_ORDER defined.
#endif
  {
     unsigned char *pd = (unsigned char *)a->dp;

     if ((unsigned)c > (FP_SIZE * sizeof(fp_digit))) {
        int excess = c - (FP_SIZE * sizeof(fp_digit));
        c -= excess;
        b += excess;
     }
     a->used = (c + sizeof(fp_digit) - 1)/sizeof(fp_digit);
     /* read the bytes in */
#ifdef BIG_ENDIAN_ORDER
     {
       /* Use Duff's device to unroll the loop. */
       int idx = (c - 1) & ~3;
       switch (c % 4) {
       case 0:	do { pd[idx+0] = *b++;
       case 3:	     pd[idx+1] = *b++;
       case 2:	     pd[idx+2] = *b++;
       case 1:	     pd[idx+3] = *b++;
                     idx -= 4;
	 	        } while ((c -= 4) > 0);
       }
     }
#else
     for (c -= 1; c >= 0; c -= 1) {
       pd[c] = *b++;
     }
#endif
  }
#else
  /* read the bytes in */
  for (; c > 0; c--) {
     fp_mul_2d (a, 8, a);
     a->dp[0] |= *b++;
     a->used += 1;
  }
#endif
  fp_clamp (a);
}

void fp_to_unsigned_bin(fp_int *a, unsigned char *b)
{
  int     x;
  fp_int  t;

  fp_init_copy(&t, a);

  x = 0;
  while (fp_iszero (&t) == FP_NO) {
      b[x++] = (unsigned char) (t.dp[0] & 255);
      fp_div_2d (&t, 8, &t, NULL);
  }
  fp_reverse (b, x);
}

int fp_unsigned_bin_size(fp_int *a)
{
  int     size = fp_count_bits (a);
  return (size / 8 + ((size & 7) != 0 ? 1 : 0));
}

void fp_set(fp_int *a, fp_digit b)
{
   fp_zero(a);
   a->dp[0] = b;
   a->used  = a->dp[0] ? 1 : 0;
}

int fp_count_bits (fp_int * a)
{
  int     r;
  fp_digit q;

  /* shortcut */
  if (a->used == 0) {
    return 0;
  }

  /* get number of digits and add that */
  r = (a->used - 1) * DIGIT_BIT;

  /* take the last digit and count the bits in it */
  q = a->dp[a->used - 1];
  while (q > ((fp_digit) 0)) {
    ++r;
    q >>= ((fp_digit) 1);
  }
  return r;
}

int fp_leading_bit(fp_int *a)
{
    int bit = 0;

    if (a->used != 0) {
        fp_digit q = a->dp[a->used - 1];
        int qSz = sizeof(fp_digit);

        while (qSz > 0) {
            if ((unsigned char)q != 0)
                bit = (q & 0x80) != 0;
            q >>= 8;
            qSz--;
        }
    }

    return bit;
}

void fp_lshd(fp_int *a, int x)
{
   int y;

   /* move up and truncate as required */
   y = MIN(a->used + x - 1, (int)(FP_SIZE-1));

   /* store new size */
   a->used = y + 1;

   /* move digits */
   for (; y >= x; y--) {
       a->dp[y] = a->dp[y-x];
   }
 
   /* zero lower digits */
   for (; y >= 0; y--) {
       a->dp[y] = 0;
   }

   /* clamp digits */
   fp_clamp(a);
}


/* right shift by bit count */
void fp_rshb(fp_int *c, int x)
{
    register fp_digit *tmpc, mask, shift;
    fp_digit r, rr;
    fp_digit D = x;

    /* mask */
    mask = (((fp_digit)1) << D) - 1;

    /* shift for lsb */
    shift = DIGIT_BIT - D;

    /* alias */
    tmpc = c->dp + (c->used - 1);

    /* carry */
    r = 0;
    for (x = c->used - 1; x >= 0; x--) {
      /* get the lower  bits of this word in a temp */
      rr = *tmpc & mask;

      /* shift the current word and mix in the carry bits from previous word */
      *tmpc = (*tmpc >> D) | (r << shift);
      --tmpc;

      /* set the carry to the carry bits of the current word found above */
      r = rr;
    }
}


void fp_rshd(fp_int *a, int x)
{
  int y;

  /* too many digits just zero and return */
  if (x >= a->used) {
     fp_zero(a);
     return;
  }

   /* shift */
   for (y = 0; y < a->used - x; y++) {
      a->dp[y] = a->dp[y+x];
   }

   /* zero rest */
   for (; y < a->used; y++) {
      a->dp[y] = 0;
   }
   
   /* decrement count */
   a->used -= x;
   fp_clamp(a);
}

/* reverse an array, used for radix code */
void fp_reverse (unsigned char *s, int len)
{
  int     ix, iy;
  unsigned char t;

  ix = 0;
  iy = len - 1;
  while (ix < iy) {
    t     = s[ix];
    s[ix] = s[iy];
    s[iy] = t;
    ++ix;
    --iy;
  }
}


/* c = a - b */
void fp_sub_d(fp_int *a, fp_digit b, fp_int *c)
{
   fp_int tmp;
   fp_set(&tmp, b);
   fp_sub(a, &tmp, c);
}


/* CyaSSL callers from normal lib */

/* init a new mp_int */
int mp_init (mp_int * a)
{
  if (a)
    fp_init(a);
  return MP_OKAY;
}

/* clear one (frees)  */
void mp_clear (mp_int * a)
{
  fp_zero(a);
}

/* handle up to 6 inits */
int mp_init_multi(mp_int* a, mp_int* b, mp_int* c, mp_int* d, mp_int* e, mp_int* f)
{
    if (a)
        fp_init(a);
    if (b)
        fp_init(b);
    if (c)
        fp_init(c);
    if (d)
        fp_init(d);
    if (e)
        fp_init(e);
    if (f)
        fp_init(f);

    return MP_OKAY;
}

/* high level addition (handles signs) */
int mp_add (mp_int * a, mp_int * b, mp_int * c)
{
  fp_add(a, b, c);
  return MP_OKAY;
}

/* high level subtraction (handles signs) */
int mp_sub (mp_int * a, mp_int * b, mp_int * c)
{
  fp_sub(a, b, c);
  return MP_OKAY;
}

/* high level multiplication (handles sign) */
int mp_mul (mp_int * a, mp_int * b, mp_int * c)
{
  fp_mul(a, b, c);
  return MP_OKAY;
}

/* d = a * b (mod c) */
int mp_mulmod (mp_int * a, mp_int * b, mp_int * c, mp_int * d)
{
  return fp_mulmod(a, b, c, d);
}

/* c = a mod b, 0 <= c < b */
int mp_mod (mp_int * a, mp_int * b, mp_int * c)
{
  return fp_mod (a, b, c);
}

/* hac 14.61, pp608 */
int mp_invmod (mp_int * a, mp_int * b, mp_int * c)
{
  return fp_invmod(a, b, c);
}

/* this is a shell function that calls either the normal or Montgomery
 * exptmod functions.  Originally the call to the montgomery code was
 * embedded in the normal function but that wasted alot of stack space
 * for nothing (since 99% of the time the Montgomery code would be called)
 */
int mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y)
{
  return fp_exptmod(G, X, P, Y);
}

/* compare two ints (signed)*/
int mp_cmp (mp_int * a, mp_int * b)
{
  return fp_cmp(a, b);
}

/* compare a digit */
int mp_cmp_d(mp_int * a, mp_digit b)
{
  return fp_cmp_d(a, b);
}

/* get the size for an unsigned equivalent */
int mp_unsigned_bin_size (mp_int * a)
{
  return fp_unsigned_bin_size(a);
}

/* store in unsigned [big endian] format */
int mp_to_unsigned_bin (mp_int * a, unsigned char *b)
{
  fp_to_unsigned_bin(a,b);
  return MP_OKAY;
}

/* reads a unsigned char array, assumes the msb is stored first [big endian] */
int mp_read_unsigned_bin (mp_int * a, const unsigned char *b, int c)
{
  fp_read_unsigned_bin(a, (unsigned char *)b, c);
  return MP_OKAY;
}


int mp_sub_d(fp_int *a, fp_digit b, fp_int *c)
{
    fp_sub_d(a, b, c);
    return MP_OKAY;
}


/* fast math conversion */
int mp_copy(fp_int* a, fp_int* b)
{
    fp_copy(a, b);
    return MP_OKAY;
}


/* fast math conversion */
int mp_isodd(mp_int* a)
{
    return fp_isodd(a);
}


/* fast math conversion */
int mp_iszero(mp_int* a)
{
    return fp_iszero(a);
}


/* fast math conversion */
int mp_count_bits (mp_int* a)
{
    return fp_count_bits(a);
}


int mp_leading_bit (mp_int* a)
{
    return fp_leading_bit(a);
}


/* fast math conversion */
void mp_rshb (mp_int* a, int x)
{
    fp_rshb(a, x);
}


/* fast math wrappers */
int mp_set_int(fp_int *a, fp_digit b)
{
    fp_set(a, b);
    return MP_OKAY;
}


#if defined(CYASSL_KEY_GEN) || defined (HAVE_ECC)

/* c = a * a (mod b) */
int fp_sqrmod(fp_int *a, fp_int *b, fp_int *c)
{
  fp_int tmp;
  fp_zero(&tmp);
  fp_sqr(a, &tmp);
  return fp_mod(&tmp, b, c);
}

/* fast math conversion */
int mp_sqrmod(mp_int *a, mp_int *b, mp_int *c)
{
    return fp_sqrmod(a, b, c);
}

/* fast math conversion */
int mp_montgomery_calc_normalization(mp_int *a, mp_int *b)
{
    fp_montgomery_calc_normalization(a, b);
    return MP_OKAY;
}

#endif /* CYASSL_KEYGEN || HAVE_ECC */


#if defined(CYASSL_KEY_GEN) || defined(HAVE_COMP_KEY)

static const int lnz[16] = {
   4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
};

/* Counts the number of lsbs which are zero before the first zero bit */
int fp_cnt_lsb(fp_int *a)
{
   int x;
   fp_digit q, qq;

   /* easy out */
   if (fp_iszero(a) == 1) {
      return 0;
   }

   /* scan lower digits until non-zero */
   for (x = 0; x < a->used && a->dp[x] == 0; x++);
   q = a->dp[x];
   x *= DIGIT_BIT;

   /* now scan this digit until a 1 is found */
   if ((q & 1) == 0) {
      do {
         qq  = q & 15;
         x  += lnz[qq];
         q >>= 4;
      } while (qq == 0);
   }
   return x;
}




static int s_is_power_of_two(fp_digit b, int *p)
{
   int x;

   /* fast return if no power of two */
   if ((b==0) || (b & (b-1))) {
      return 0;
   }

   for (x = 0; x < DIGIT_BIT; x++) {
      if (b == (((fp_digit)1)<<x)) {
         *p = x;
         return 1;
      }
   }
   return 0;
}

/* a/b => cb + d == a */
static int fp_div_d(fp_int *a, fp_digit b, fp_int *c, fp_digit *d)
{
  fp_int   q;
  fp_word  w;
  fp_digit t;
  int      ix;

  /* cannot divide by zero */
  if (b == 0) {
     return FP_VAL;
  }

  /* quick outs */
  if (b == 1 || fp_iszero(a) == 1) {
     if (d != NULL) {
        *d = 0;
     }
     if (c != NULL) {
        fp_copy(a, c);
     }
     return FP_OKAY;
  }

  /* power of two ? */
  if (s_is_power_of_two(b, &ix) == 1) {
     if (d != NULL) {
        *d = a->dp[0] & ((((fp_digit)1)<<ix) - 1);
     }
     if (c != NULL) {
        fp_div_2d(a, ix, c, NULL);
     }
     return FP_OKAY;
  }

  /* no easy answer [c'est la vie].  Just division */
  fp_init(&q);
  
  q.used = a->used;
  q.sign = a->sign;
  w = 0;
  for (ix = a->used - 1; ix >= 0; ix--) {
     w = (w << ((fp_word)DIGIT_BIT)) | ((fp_word)a->dp[ix]);
     
     if (w >= b) {
        t = (fp_digit)(w / b);
        w -= ((fp_word)t) * ((fp_word)b);
      } else {
        t = 0;
      }
      q.dp[ix] = (fp_digit)t;
  }
  
  if (d != NULL) {
     *d = (fp_digit)w;
  }
  
  if (c != NULL) {
     fp_clamp(&q);
     fp_copy(&q, c);
  }
 
  return FP_OKAY;
}


/* c = a mod b, 0 <= c < b  */
static int fp_mod_d(fp_int *a, fp_digit b, fp_digit *c)
{
   return fp_div_d(a, b, NULL, c);
}

int mp_mod_d(fp_int *a, fp_digit b, fp_digit *c)
{
   return fp_mod_d(a, b, c);
}

#endif /* defined(CYASSL_KEY_GEN) || defined(HAVE_COMP_KEY) */

#ifdef CYASSL_KEY_GEN

void fp_gcd(fp_int *a, fp_int *b, fp_int *c);
void fp_lcm(fp_int *a, fp_int *b, fp_int *c);
int  fp_isprime(fp_int *a);

int mp_gcd(fp_int *a, fp_int *b, fp_int *c)
{
    fp_gcd(a, b, c);
    return MP_OKAY;
}


int mp_lcm(fp_int *a, fp_int *b, fp_int *c)
{
    fp_lcm(a, b, c);
    return MP_OKAY;
}


int mp_prime_is_prime(mp_int* a, int t, int* result)
{
    (void)t;
    *result = fp_isprime(a);
    return MP_OKAY;
}

/* Miller-Rabin test of "a" to the base of "b" as described in 
 * HAC pp. 139 Algorithm 4.24
 *
 * Sets result to 0 if definitely composite or 1 if probably prime.
 * Randomly the chance of error is no more than 1/4 and often 
 * very much lower.
 */
static void fp_prime_miller_rabin (fp_int * a, fp_int * b, int *result)
{
  fp_int  n1, y, r;
  int     s, j;

  /* default */
  *result = FP_NO;

  /* ensure b > 1 */
  if (fp_cmp_d(b, 1) != FP_GT) {
     return;
  }     

  /* get n1 = a - 1 */
  fp_init_copy(&n1, a);
  fp_sub_d(&n1, 1, &n1);

  /* set 2**s * r = n1 */
  fp_init_copy(&r, &n1);

  /* count the number of least significant bits
   * which are zero
   */
  s = fp_cnt_lsb(&r);

  /* now divide n - 1 by 2**s */
  fp_div_2d (&r, s, &r, NULL);

  /* compute y = b**r mod a */
  fp_init(&y);
  fp_exptmod(b, &r, a, &y);

  /* if y != 1 and y != n1 do */
  if (fp_cmp_d (&y, 1) != FP_EQ && fp_cmp (&y, &n1) != FP_EQ) {
    j = 1;
    /* while j <= s-1 and y != n1 */
    while ((j <= (s - 1)) && fp_cmp (&y, &n1) != FP_EQ) {
      fp_sqrmod (&y, a, &y);

      /* if y == 1 then composite */
      if (fp_cmp_d (&y, 1) == FP_EQ) {
         return;
      }
      ++j;
    }

    /* if y != n1 then composite */
    if (fp_cmp (&y, &n1) != FP_EQ) {
       return;
    }
  }

  /* probably prime now */
  *result = FP_YES;
}


/* a few primes */
static const fp_digit primes[256] = {
  0x0002, 0x0003, 0x0005, 0x0007, 0x000B, 0x000D, 0x0011, 0x0013,
  0x0017, 0x001D, 0x001F, 0x0025, 0x0029, 0x002B, 0x002F, 0x0035,
  0x003B, 0x003D, 0x0043, 0x0047, 0x0049, 0x004F, 0x0053, 0x0059,
  0x0061, 0x0065, 0x0067, 0x006B, 0x006D, 0x0071, 0x007F, 0x0083,
  0x0089, 0x008B, 0x0095, 0x0097, 0x009D, 0x00A3, 0x00A7, 0x00AD,
  0x00B3, 0x00B5, 0x00BF, 0x00C1, 0x00C5, 0x00C7, 0x00D3, 0x00DF,
  0x00E3, 0x00E5, 0x00E9, 0x00EF, 0x00F1, 0x00FB, 0x0101, 0x0107,
  0x010D, 0x010F, 0x0115, 0x0119, 0x011B, 0x0125, 0x0133, 0x0137,

  0x0139, 0x013D, 0x014B, 0x0151, 0x015B, 0x015D, 0x0161, 0x0167,
  0x016F, 0x0175, 0x017B, 0x017F, 0x0185, 0x018D, 0x0191, 0x0199,
  0x01A3, 0x01A5, 0x01AF, 0x01B1, 0x01B7, 0x01BB, 0x01C1, 0x01C9,
  0x01CD, 0x01CF, 0x01D3, 0x01DF, 0x01E7, 0x01EB, 0x01F3, 0x01F7,
  0x01FD, 0x0209, 0x020B, 0x021D, 0x0223, 0x022D, 0x0233, 0x0239,
  0x023B, 0x0241, 0x024B, 0x0251, 0x0257, 0x0259, 0x025F, 0x0265,
  0x0269, 0x026B, 0x0277, 0x0281, 0x0283, 0x0287, 0x028D, 0x0293,
  0x0295, 0x02A1, 0x02A5, 0x02AB, 0x02B3, 0x02BD, 0x02C5, 0x02CF,

  0x02D7, 0x02DD, 0x02E3, 0x02E7, 0x02EF, 0x02F5, 0x02F9, 0x0301,
  0x0305, 0x0313, 0x031D, 0x0329, 0x032B, 0x0335, 0x0337, 0x033B,
  0x033D, 0x0347, 0x0355, 0x0359, 0x035B, 0x035F, 0x036D, 0x0371,
  0x0373, 0x0377, 0x038B, 0x038F, 0x0397, 0x03A1, 0x03A9, 0x03AD,
  0x03B3, 0x03B9, 0x03C7, 0x03CB, 0x03D1, 0x03D7, 0x03DF, 0x03E5,
  0x03F1, 0x03F5, 0x03FB, 0x03FD, 0x0407, 0x0409, 0x040F, 0x0419,
  0x041B, 0x0425, 0x0427, 0x042D, 0x043F, 0x0443, 0x0445, 0x0449,
  0x044F, 0x0455, 0x045D, 0x0463, 0x0469, 0x047F, 0x0481, 0x048B,

  0x0493, 0x049D, 0x04A3, 0x04A9, 0x04B1, 0x04BD, 0x04C1, 0x04C7,
  0x04CD, 0x04CF, 0x04D5, 0x04E1, 0x04EB, 0x04FD, 0x04FF, 0x0503,
  0x0509, 0x050B, 0x0511, 0x0515, 0x0517, 0x051B, 0x0527, 0x0529,
  0x052F, 0x0551, 0x0557, 0x055D, 0x0565, 0x0577, 0x0581, 0x058F,
  0x0593, 0x0595, 0x0599, 0x059F, 0x05A7, 0x05AB, 0x05AD, 0x05B3,
  0x05BF, 0x05C9, 0x05CB, 0x05CF, 0x05D1, 0x05D5, 0x05DB, 0x05E7,
  0x05F3, 0x05FB, 0x0607, 0x060D, 0x0611, 0x0617, 0x061F, 0x0623,
  0x062B, 0x062F, 0x063D, 0x0641, 0x0647, 0x0649, 0x064D, 0x0653
};

int fp_isprime(fp_int *a)
{
   fp_int   b;
   fp_digit d = 0;
   int      r, res;

   /* do trial division */
   for (r = 0; r < 256; r++) {
       fp_mod_d(a, primes[r], &d);
       if (d == 0) {
          return FP_NO;
       }
   }

   /* now do 8 miller rabins */
   fp_init(&b);
   for (r = 0; r < 8; r++) {
       fp_set(&b, primes[r]);
       fp_prime_miller_rabin(a, &b, &res);
       if (res == FP_NO) {
          return FP_NO;
       }
   }
   return FP_YES;
}


/* c = [a, b] */
void fp_lcm(fp_int *a, fp_int *b, fp_int *c)
{
   fp_int  t1, t2;

   fp_init(&t1);
   fp_init(&t2);
   fp_gcd(a, b, &t1);
   if (fp_cmp_mag(a, b) == FP_GT) {
      fp_div(a, &t1, &t2, NULL);
      fp_mul(b, &t2, c);
   } else {
      fp_div(b, &t1, &t2, NULL);
      fp_mul(a, &t2, c);
   }   
}



/* c = (a, b) */
void fp_gcd(fp_int *a, fp_int *b, fp_int *c)
{
   fp_int u, v, r;

   /* either zero than gcd is the largest */
   if (fp_iszero (a) == 1 && fp_iszero (b) == 0) {
     fp_abs (b, c);
     return;
   }
   if (fp_iszero (a) == 0 && fp_iszero (b) == 1) {
     fp_abs (a, c);
     return;
   }

   /* optimized.  At this point if a == 0 then
    * b must equal zero too
    */
   if (fp_iszero (a) == 1) {
     fp_zero(c);
     return;
   }

   /* sort inputs */
   if (fp_cmp_mag(a, b) != FP_LT) {
      fp_init_copy(&u, a);
      fp_init_copy(&v, b);
   } else {
      fp_init_copy(&u, b);
      fp_init_copy(&v, a);
   }
 
   fp_zero(&r);
   while (fp_iszero(&v) == FP_NO) {
      fp_mod(&u, &v, &r);
      fp_copy(&v, &u);
      fp_copy(&r, &v);
   }
   fp_copy(&u, c);
}

#endif /* CYASSL_KEY_GEN */


#if defined(HAVE_ECC) || !defined(NO_PWDBASED)
/* c = a + b */
void fp_add_d(fp_int *a, fp_digit b, fp_int *c)
{
   fp_int tmp;
   fp_set(&tmp, b);
   fp_add(a,&tmp,c);
}

/* external compatibility */
int mp_add_d(fp_int *a, fp_digit b, fp_int *c)
{
    fp_add_d(a, b, c);
    return MP_OKAY;
}

#endif  /* HAVE_ECC || !NO_PWDBASED */


#ifdef HAVE_ECC

/* chars used in radix conversions */
static const char *fp_s_rmap = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz+/";

static int fp_read_radix(fp_int *a, const char *str, int radix)
{
  int     y, neg;
  char    ch;

  /* make sure the radix is ok */
  if (radix < 2 || radix > 64) {
    return FP_VAL;
  }

  /* if the leading digit is a
   * minus set the sign to negative.
   */
  if (*str == '-') {
    ++str;
    neg = FP_NEG;
  } else {
    neg = FP_ZPOS;
  }

  /* set the integer to the default of zero */
  fp_zero (a);

  /* process each digit of the string */
  while (*str) {
    /* if the radix < 36 the conversion is case insensitive
     * this allows numbers like 1AB and 1ab to represent the same  value
     * [e.g. in hex]
     */
    ch = (char) ((radix < 36) ? XTOUPPER(*str) : *str);
    for (y = 0; y < 64; y++) {
      if (ch == fp_s_rmap[y]) {
         break;
      }
    }

    /* if the char was found in the map
     * and is less than the given radix add it
     * to the number, otherwise exit the loop.
     */
    if (y < radix) {
      fp_mul_d (a, (fp_digit) radix, a);
      fp_add_d (a, (fp_digit) y, a);
    } else {
      break;
    }
    ++str;
  }

  /* set the sign only if a != 0 */
  if (fp_iszero(a) != FP_YES) {
     a->sign = neg;
  }
  return FP_OKAY;
}

/* fast math conversion */
int mp_read_radix(mp_int *a, const char *str, int radix)
{
    return fp_read_radix(a, str, radix);
}

/* fast math conversion */
int mp_set(fp_int *a, fp_digit b)
{
    fp_set(a,b);
    return MP_OKAY;
}

/* fast math conversion */
int mp_sqr(fp_int *A, fp_int *B)
{
    fp_sqr(A, B);
    return MP_OKAY;
}
  
/* fast math conversion */
int mp_montgomery_reduce(fp_int *a, fp_int *m, fp_digit mp)
{
    fp_montgomery_reduce(a, m, mp);
    return MP_OKAY;
}


/* fast math conversion */
int mp_montgomery_setup(fp_int *a, fp_digit *rho)
{
    return fp_montgomery_setup(a, rho);
}

int mp_div_2(fp_int * a, fp_int * b)
{
    fp_div_2(a, b);
    return MP_OKAY;
}


int mp_init_copy(fp_int * a, fp_int * b)
{
    fp_init_copy(a, b);
    return MP_OKAY;
}


#ifdef HAVE_COMP_KEY

int mp_cnt_lsb(fp_int* a)
{
    fp_cnt_lsb(a);
    return MP_OKAY;
}

int mp_div_2d(fp_int* a, int b, fp_int* c, fp_int* d)
{
    fp_div_2d(a, b, c, d);
    return MP_OKAY;
}

#endif /* HAVE_COMP_KEY */


#endif /* HAVE_ECC */

#endif /* USE_FAST_MATH */
