Mercurial > dropbear
view libtommath/bn_s_mp_mul_digs.c @ 1613:caa9bb54dfa0
fix #endif (#59)
author | François Perrad <francois.perrad@gadz.org> |
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date | Wed, 28 Feb 2018 15:10:14 +0100 |
parents | 8bba51a55704 |
children | f52919ffd3b1 |
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#include <tommath_private.h> #ifdef BN_S_MP_MUL_DIGS_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, [email protected], http://libtom.org */ /* 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. */ int s_mp_mul_digs (mp_int * a, 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; /* 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; /* 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); /* 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) 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 /* ref: $Format:%D$ */ /* git commit: $Format:%H$ */ /* commit time: $Format:%ai$ */