blob: 1c0aae4322a55eff92e66b4809c7cd22b1bf7a29 [file] [log] [blame]
 #include #ifdef BN_S_MP_MUL_HIGH_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, tomstdenis@gmail.com, http://math.libtomcrypt.com */ /* multiplies |a| * |b| and does not compute the lower digs digits * [meant to get the higher part of the product] */ int s_mp_mul_high_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? */ #ifdef BN_FAST_S_MP_MUL_HIGH_DIGS_C if (((a->used + b->used + 1) < MP_WARRAY) && MIN (a->used, b->used) < (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) { return fast_s_mp_mul_high_digs (a, b, c, digs); } #endif if ((res = mp_init_size (&t, a->used + b->used + 1)) != MP_OKAY) { return res; } t.used = a->used + b->used + 1; pa = a->used; pb = b->used; for (ix = 0; ix < pa; ix++) { /* clear the carry */ u = 0; /* left hand side of A[ix] * B[iy] */ tmpx = a->dp[ix]; /* alias to the address of where the digits will be stored */ tmpt = &(t.dp[digs]); /* alias for where to read the right hand side from */ tmpy = b->dp + (digs - ix); for (iy = digs - ix; iy < pb; iy++) { /* calculate the double precision result */ r = ((mp_word)*tmpt) + ((mp_word)tmpx) * ((mp_word)*tmpy++) + ((mp_word) u); /* get the lower part */ *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK)); /* carry the carry */ u = (mp_digit) (r >> ((mp_word) DIGIT_BIT)); } *tmpt = u; } mp_clamp (&t); mp_exch (&t, c); mp_clear (&t); return MP_OKAY; } #endif /* \$Source: /cvs/libtom/libtommath/bn_s_mp_mul_high_digs.c,v \$ */ /* \$Revision: 1.3 \$ */ /* \$Date: 2006/03/31 14:18:44 \$ */