1 #include <tommath.h> 2 #ifdef BN_MP_MUL_D_C 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis 4 * 5 * LibTomMath is a library that provides multiple-precision 6 * integer arithmetic as well as number theoretic functionality. 7 * 8 * The library was designed directly after the MPI library by 9 * Michael Fromberger but has been written from scratch with 10 * additional optimizations in place. 11 * 12 * The library is free for all purposes without any express 13 * guarantee it works. 14 * 15 * Tom St Denis, tomstdenis (at) gmail.com, http://math.libtomcrypt.com 16 */ 17 18 /* multiply by a digit */ 19 int 20 mp_mul_d (mp_int * a, mp_digit b, mp_int * c) 21 { 22 mp_digit u, *tmpa, *tmpc; 23 mp_word r; 24 int ix, res, olduse; 25 26 /* make sure c is big enough to hold a*b */ 27 if (c->alloc < a->used + 1) { 28 if ((res = mp_grow (c, a->used + 1)) != MP_OKAY) { 29 return res; 30 } 31 } 32 33 /* get the original destinations used count */ 34 olduse = c->used; 35 36 /* set the sign */ 37 c->sign = a->sign; 38 39 /* alias for a->dp [source] */ 40 tmpa = a->dp; 41 42 /* alias for c->dp [dest] */ 43 tmpc = c->dp; 44 45 /* zero carry */ 46 u = 0; 47 48 /* compute columns */ 49 for (ix = 0; ix < a->used; ix++) { 50 /* compute product and carry sum for this term */ 51 r = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b); 52 53 /* mask off higher bits to get a single digit */ 54 *tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK)); 55 56 /* send carry into next iteration */ 57 u = (mp_digit) (r >> ((mp_word) DIGIT_BIT)); 58 } 59 60 /* store final carry [if any] and increment ix offset */ 61 *tmpc++ = u; 62 ++ix; 63 64 /* now zero digits above the top */ 65 while (ix++ < olduse) { 66 *tmpc++ = 0; 67 } 68 69 /* set used count */ 70 c->used = a->used + 1; 71 mp_clamp(c); 72 73 return MP_OKAY; 74 } 75 #endif 76 77 /* $Source: /cvs/libtom/libtommath/bn_mp_mul_d.c,v $ */ 78 /* $Revision: 1.3 $ */ 79 /* $Date: 2006/03/31 14:18:44 $ */ 80
