1 #include <tommath.h> 2 #ifdef BN_MP_2EXPT_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 /* computes a = 2**b 19 * 20 * Simple algorithm which zeroes the int, grows it then just sets one bit 21 * as required. 22 */ 23 int 24 mp_2expt (mp_int * a, int b) 25 { 26 int res; 27 28 /* zero a as per default */ 29 mp_zero (a); 30 31 /* grow a to accomodate the single bit */ 32 if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) { 33 return res; 34 } 35 36 /* set the used count of where the bit will go */ 37 a->used = b / DIGIT_BIT + 1; 38 39 /* put the single bit in its place */ 40 a->dp[b / DIGIT_BIT] = ((mp_digit)1) << (b % DIGIT_BIT); 41 42 return MP_OKAY; 43 } 44 #endif 45 46 /* $Source: /cvs/libtom/libtommath/bn_mp_2expt.c,v $ */ 47 /* $Revision: 1.3 $ */ 48 /* $Date: 2006/03/31 14:18:44 $ */ 49
