diff options
Diffstat (limited to 'libtommath/bn_s_mp_mul_digs.c')
| -rw-r--r-- | libtommath/bn_s_mp_mul_digs.c | 114 |
1 files changed, 58 insertions, 56 deletions
diff --git a/libtommath/bn_s_mp_mul_digs.c b/libtommath/bn_s_mp_mul_digs.c index 401f32e..442c803 100644 --- a/libtommath/bn_s_mp_mul_digs.c +++ b/libtommath/bn_s_mp_mul_digs.c @@ -1,4 +1,4 @@ -#include <tommath.h> +#include "tommath_private.h" #ifdef BN_S_MP_MUL_DIGS_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * @@ -11,76 +11,78 @@ * * The library is free for all purposes without any express * guarantee it works. - * - * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com */ /* multiplies |a| * |b| and only computes upto digs digits of result - * HAC pp. 595, Algorithm 14.12 Modified so you can control how + * HAC pp. 595, Algorithm 14.12 Modified so you can control how * many digits of output are created. */ -int s_mp_mul_digs (mp_int * a, mp_int * b, mp_int * c, int digs) +int s_mp_mul_digs(const mp_int *a, const mp_int *b, mp_int *c, int digs) { - mp_int t; - int res, pa, pb, ix, iy; - mp_digit u; - mp_word r; - mp_digit tmpx, *tmpt, *tmpy; + mp_int t; + int res, pa, pb, ix, iy; + mp_digit u; + mp_word r; + mp_digit tmpx, *tmpt, *tmpy; + + /* can we use the fast multiplier? */ + if ((digs < (int)MP_WARRAY) && + (MIN(a->used, b->used) < + (int)(1u << (((size_t)CHAR_BIT * sizeof(mp_word)) - (2u * (size_t)DIGIT_BIT))))) { + return fast_s_mp_mul_digs(a, b, c, digs); + } - /* can we use the fast multiplier? */ - if (((digs) < MP_WARRAY) && - MIN (a->used, b->used) < - (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) { - return fast_s_mp_mul_digs (a, b, c, digs); - } + if ((res = mp_init_size(&t, digs)) != MP_OKAY) { + return res; + } + t.used = digs; - if ((res = mp_init_size (&t, digs)) != MP_OKAY) { - return res; - } - t.used = digs; + /* compute the digits of the product directly */ + pa = a->used; + for (ix = 0; ix < pa; ix++) { + /* set the carry to zero */ + u = 0; - /* compute the digits of the product directly */ - pa = a->used; - for (ix = 0; ix < pa; ix++) { - /* set the carry to zero */ - u = 0; + /* limit ourselves to making digs digits of output */ + pb = MIN(b->used, digs - ix); - /* limit ourselves to making digs digits of output */ - pb = MIN (b->used, digs - ix); + /* setup some aliases */ + /* copy of the digit from a used within the nested loop */ + tmpx = a->dp[ix]; - /* setup some aliases */ - /* copy of the digit from a used within the nested loop */ - tmpx = a->dp[ix]; - - /* an alias for the destination shifted ix places */ - tmpt = t.dp + ix; - - /* an alias for the digits of b */ - tmpy = b->dp; + /* an alias for the destination shifted ix places */ + tmpt = t.dp + ix; - /* compute the columns of the output and propagate the carry */ - for (iy = 0; iy < pb; iy++) { - /* compute the column as a mp_word */ - r = ((mp_word)*tmpt) + - ((mp_word)tmpx) * ((mp_word)*tmpy++) + - ((mp_word) u); + /* an alias for the digits of b */ + tmpy = b->dp; - /* the new column is the lower part of the result */ - *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK)); + /* compute the columns of the output and propagate the carry */ + for (iy = 0; iy < pb; iy++) { + /* compute the column as a mp_word */ + r = (mp_word)*tmpt + + ((mp_word)tmpx * (mp_word)*tmpy++) + + (mp_word)u; - /* get the carry word from the result */ - u = (mp_digit) (r >> ((mp_word) DIGIT_BIT)); - } - /* set carry if it is placed below digs */ - if (ix + iy < digs) { - *tmpt = u; - } - } + /* the new column is the lower part of the result */ + *tmpt++ = (mp_digit)(r & (mp_word)MP_MASK); - mp_clamp (&t); - mp_exch (&t, c); + /* get the carry word from the result */ + u = (mp_digit)(r >> (mp_word)DIGIT_BIT); + } + /* set carry if it is placed below digs */ + if ((ix + iy) < digs) { + *tmpt = u; + } + } - mp_clear (&t); - return MP_OKAY; + mp_clamp(&t); + mp_exch(&t, c); + + mp_clear(&t); + return MP_OKAY; } #endif + +/* ref: $Format:%D$ */ +/* git commit: $Format:%H$ */ +/* commit time: $Format:%ai$ */ |