1 #include <tommath.h> 2 #ifdef BN_MP_LSHD_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@gmail.com, http://math.libtomcrypt.com 16 */ 17 18 /* shift left a certain amount of digits */ mp_lshd(mp_int * a,int b)19int mp_lshd (mp_int * a, int b) 20 { 21 int x, res; 22 23 /* if its less than zero return */ 24 if (b <= 0) { 25 return MP_OKAY; 26 } 27 28 /* grow to fit the new digits */ 29 if (a->alloc < a->used + b) { 30 if ((res = mp_grow (a, a->used + b)) != MP_OKAY) { 31 return res; 32 } 33 } 34 35 { 36 register mp_digit *top, *bottom; 37 38 /* increment the used by the shift amount then copy upwards */ 39 a->used += b; 40 41 /* top */ 42 top = a->dp + a->used - 1; 43 44 /* base */ 45 bottom = a->dp + a->used - 1 - b; 46 47 /* much like mp_rshd this is implemented using a sliding window 48 * except the window goes the otherway around. Copying from 49 * the bottom to the top. see bn_mp_rshd.c for more info. 50 */ 51 for (x = a->used - 1; x >= b; x--) { 52 *top-- = *bottom--; 53 } 54 55 /* zero the lower digits */ 56 top = a->dp; 57 for (x = 0; x < b; x++) { 58 *top++ = 0; 59 } 60 } 61 return MP_OKAY; 62 } 63 #endif 64 65 /* $Source: /cvs/libtom/libtommath/bn_mp_lshd.c,v $ */ 66 /* $Revision: 1.3 $ */ 67 /* $Date: 2006/03/31 14:18:44 $ */ 68