1 #include <tommath.h> 2 #ifdef BN_MP_MUL_2_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 /* b = a*2 */ 19 int mp_mul_2(mp_int * a, mp_int * b) 20 { 21 int x, res, oldused; 22 23 /* grow to accomodate result */ 24 if (b->alloc < a->used + 1) { 25 if ((res = mp_grow (b, a->used + 1)) != MP_OKAY) { 26 return res; 27 } 28 } 29 30 oldused = b->used; 31 b->used = a->used; 32 33 { 34 register mp_digit r, rr, *tmpa, *tmpb; 35 36 /* alias for source */ 37 tmpa = a->dp; 38 39 /* alias for dest */ 40 tmpb = b->dp; 41 42 /* carry */ 43 r = 0; 44 for (x = 0; x < a->used; x++) { 45 46 /* get what will be the *next* carry bit from the 47 * MSB of the current digit 48 */ 49 rr = *tmpa >> ((mp_digit)(DIGIT_BIT - 1)); 50 51 /* now shift up this digit, add in the carry [from the previous] */ 52 *tmpb++ = ((*tmpa++ << ((mp_digit)1)) | r) & MP_MASK; 53 54 /* copy the carry that would be from the source 55 * digit into the next iteration 56 */ 57 r = rr; 58 } 59 60 /* new leading digit? */ 61 if (r != 0) { 62 /* add a MSB which is always 1 at this point */ 63 *tmpb = 1; 64 ++(b->used); 65 } 66 67 /* now zero any excess digits on the destination 68 * that we didn't write to 69 */ 70 tmpb = b->dp + b->used; 71 for (x = b->used; x < oldused; x++) { 72 *tmpb++ = 0; 73 } 74 } 75 b->sign = a->sign; 76 return MP_OKAY; 77 } 78 #endif 79 80 /* $Source: /cvs/libtom/libtommath/bn_mp_mul_2.c,v $ */ 81 /* $Revision: 1.3 $ */ 82 /* $Date: 2006/03/31 14:18:44 $ */ 83
