1 /* $NetBSD: bn_mp_expt_d.c,v 1.1.1.1 2011/04/13 18:14:54 elric Exp $ */ 2 3 #include <tommath.h> 4 #ifdef BN_MP_EXPT_D_C 5 /* LibTomMath, multiple-precision integer library -- Tom St Denis 6 * 7 * LibTomMath is a library that provides multiple-precision 8 * integer arithmetic as well as number theoretic functionality. 9 * 10 * The library was designed directly after the MPI library by 11 * Michael Fromberger but has been written from scratch with 12 * additional optimizations in place. 13 * 14 * The library is free for all purposes without any express 15 * guarantee it works. 16 * 17 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org 18 */ 19 20 /* calculate c = a**b using a square-multiply algorithm */ 21 int mp_expt_d (mp_int * a, mp_digit b, mp_int * c) 22 { 23 int res, x; 24 mp_int g; 25 26 if ((res = mp_init_copy (&g, a)) != MP_OKAY) { 27 return res; 28 } 29 30 /* set initial result */ 31 mp_set (c, 1); 32 33 for (x = 0; x < (int) DIGIT_BIT; x++) { 34 /* square */ 35 if ((res = mp_sqr (c, c)) != MP_OKAY) { 36 mp_clear (&g); 37 return res; 38 } 39 40 /* if the bit is set multiply */ 41 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) { 42 if ((res = mp_mul (c, &g, c)) != MP_OKAY) { 43 mp_clear (&g); 44 return res; 45 } 46 } 47 48 /* shift to next bit */ 49 b <<= 1; 50 } 51 52 mp_clear (&g); 53 return MP_OKAY; 54 } 55 #endif 56 57 /* Source: /cvs/libtom/libtommath/bn_mp_expt_d.c,v */ 58 /* Revision: 1.4 */ 59 /* Date: 2006/12/28 01:25:13 */ 60