1 /* $NetBSD: bn_mp_mod_2d.c,v 1.1.1.1 2011/04/13 18:14:54 elric Exp $ */ 2 3 #include <tommath.h> 4 #ifdef BN_MP_MOD_2D_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 /* calc a value mod 2**b */ 21 int 22 mp_mod_2d (mp_int * a, int b, mp_int * c) 23 { 24 int x, res; 25 26 /* if b is <= 0 then zero the int */ 27 if (b <= 0) { 28 mp_zero (c); 29 return MP_OKAY; 30 } 31 32 /* if the modulus is larger than the value than return */ 33 if (b >= (int) (a->used * DIGIT_BIT)) { 34 res = mp_copy (a, c); 35 return res; 36 } 37 38 /* copy */ 39 if ((res = mp_copy (a, c)) != MP_OKAY) { 40 return res; 41 } 42 43 /* zero digits above the last digit of the modulus */ 44 for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) { 45 c->dp[x] = 0; 46 } 47 /* clear the digit that is not completely outside/inside the modulus */ 48 c->dp[b / DIGIT_BIT] &= 49 (mp_digit) ((((mp_digit) 1) << (((mp_digit) b) % DIGIT_BIT)) - ((mp_digit) 1)); 50 mp_clamp (c); 51 return MP_OKAY; 52 } 53 #endif 54 55 /* Source: /cvs/libtom/libtommath/bn_mp_mod_2d.c,v */ 56 /* Revision: 1.4 */ 57 /* Date: 2006/12/28 01:25:13 */ 58