C++ (Cpp) s_fp_sub Examples

Example #1

File: fp_add.c Project: gapry/sel4-tomsfastmath

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);
    }
  }
}

Example #2

File: fp_montgomery_calc_normalization.c Project: DarkenCode/yafu

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

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

  /* compute A = B^(n-1) * 2^(bits-1) */
  if (b->size > 1) {
     fp_2expt (a, (b->size - 1) * BITS_PER_DIGIT + bits - 1);
  } else {
	  //printf("b.size == 1\n");
     sp2z((fp_digit)1,a);
     bits = 1;
  }

  /* now compute C = A * B mod b */
  for (x = bits - 1; x < (int)BITS_PER_DIGIT; x++) {
    fp_mul_2 (a, a);
	//  zShiftLeft(a,a,1);
    if (fp_cmp_mag (a, b) != FP_LT) {
      s_fp_sub (a, b, a);
    }
	  //if (zCompare(a,b) > 0)
		//  zSub(a,b,a);
  }
}

Example #3

File: fp_montgomery_calc_normalization.c Project: SquadroneSystem/vrbrain_nuttx

/* 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);
    }
  }
}

Example #4

File: fp_montgomery_reduce.c Project: Rupan/tomsfastmath

/* 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;
   int      oldused, x, y, pa;

   /* bail if too large */
   if (m->used > (FP_SIZE/2)) {
      return;
   }

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

#if defined(USE_MEMSET)
   /* now zero the buff */
   memset(c, 0, sizeof c);
#endif
   pa = m->used;

   /* copy the input */
   oldused = a->used;
   for (x = 0; x < oldused; x++) {
       c[x] = a->dp[x];
   }
#if !defined(USE_MEMSET)
   for (; x < 2*pa+1; x++) {
       c[x] = 0;
   }
#endif
   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);
  }
}