1 #include <tommath.h> 2 #ifdef BN_MP_DIV_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_div_2(mp_int * a, mp_int * b) 20 { 21 int x, res, oldused; 22 23 /* copy */ 24 if (b->alloc < a->used) { 25 if ((res = mp_grow (b, a->used)) != MP_OKAY) { 26 return res; 27 } 28 } 29 30 oldused = b->used; 31 b->used = a->used; 32 { 33 register mp_digit r, rr, *tmpa, *tmpb; 34 35 /* source alias */ 36 tmpa = a->dp + b->used - 1; 37 38 /* dest alias */ 39 tmpb = b->dp + b->used - 1; 40 41 /* carry */ 42 r = 0; 43 for (x = b->used - 1; x >= 0; x--) { 44 /* get the carry for the next iteration */ 45 rr = *tmpa & 1; 46 47 /* shift the current digit, add in carry and store */ 48 *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1)); 49 50 /* forward carry to next iteration */ 51 r = rr; 52 } 53 54 /* zero excess digits */ 55 tmpb = b->dp + b->used; 56 for (x = b->used; x < oldused; x++) { 57 *tmpb++ = 0; 58 } 59 } 60 b->sign = a->sign; 61 mp_clamp (b); 62 return MP_OKAY; 63 } 64 #endif 65 66 /* $Source: /cvs/libtom/libtommath/bn_mp_div_2.c,v $ */ 67 /* $Revision: 1.3 $ */ 68 /* $Date: 2006/03/31 14:18:44 $ */ 69
