1 #include <tommath.h> 2 #ifdef BN_MP_EXPT_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 /* calculate c = a**b using a square-multiply algorithm */ 19 int mp_expt_d (mp_int * a, mp_digit b, mp_int * c) 20 { 21 int res, x; 22 mp_int g; 23 24 if ((res = mp_init_copy (&g, a)) != MP_OKAY) { 25 return res; 26 } 27 28 /* set initial result */ 29 mp_set (c, 1); 30 31 for (x = 0; x < (int) DIGIT_BIT; x++) { 32 /* square */ 33 if ((res = mp_sqr (c, c)) != MP_OKAY) { 34 mp_clear (&g); 35 return res; 36 } 37 38 /* if the bit is set multiply */ 39 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) { 40 if ((res = mp_mul (c, &g, c)) != MP_OKAY) { 41 mp_clear (&g); 42 return res; 43 } 44 } 45 46 /* shift to next bit */ 47 b <<= 1; 48 } 49 50 mp_clear (&g); 51 return MP_OKAY; 52 } 53 #endif 54 55 /* $Source: /cvs/libtom/libtommath/bn_mp_expt_d.c,v $ */ 56 /* $Revision: 1.3 $ */ 57 /* $Date: 2006/03/31 14:18:44 $ */ 58
