Mercurial > dropbear
view libtommath/bn_s_mp_mul_digs.c @ 1723:5386011b740d
Disable toom and karatsuba for new libtommath
author | Matt Johnston <matt@ucc.asn.au> |
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date | Thu, 18 Jun 2020 19:12:07 +0800 |
parents | 1051e4eea25a |
children |
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#include "tommath_private.h" #ifdef BN_S_MP_MUL_DIGS_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* multiplies |a| * |b| and only computes upto digs digits of result * HAC pp. 595, Algorithm 14.12 Modified so you can control how * many digits of output are created. */ mp_err s_mp_mul_digs(const mp_int *a, const mp_int *b, mp_int *c, int digs) { mp_int t; mp_err err; int pa, pb, ix, iy; mp_digit u; mp_word r; mp_digit tmpx, *tmpt, *tmpy; /* can we use the fast multiplier? */ if ((digs < MP_WARRAY) && (MP_MIN(a->used, b->used) < MP_MAXFAST)) { return s_mp_mul_digs_fast(a, b, c, digs); } if ((err = mp_init_size(&t, digs)) != MP_OKAY) { return err; } 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; /* limit ourselves to making digs digits of output */ pb = MP_MIN(b->used, digs - 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; /* 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; /* the new column is the lower part of the result */ *tmpt++ = (mp_digit)(r & (mp_word)MP_MASK); /* get the carry word from the result */ u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT); } /* set carry if it is placed below digs */ if ((ix + iy) < digs) { *tmpt = u; } } mp_clamp(&t); mp_exch(&t, c); mp_clear(&t); return MP_OKAY; } #endif