## File: bn_mp_expt_d.c

package info (click to toggle)
libtommath 0.42.0-1
 `123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657` ``````#include #ifdef BN_MP_EXPT_D_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, tomstdenis@gmail.com, http://libtom.org */ /* calculate c = a**b using a square-multiply algorithm */ int mp_expt_d (mp_int * a, mp_digit b, mp_int * c) { int res, x; mp_int g; if ((res = mp_init_copy (&g, a)) != MP_OKAY) { return res; } /* set initial result */ mp_set (c, 1); for (x = 0; x < (int) DIGIT_BIT; x++) { /* square */ if ((res = mp_sqr (c, c)) != MP_OKAY) { mp_clear (&g); return res; } /* if the bit is set multiply */ if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) { if ((res = mp_mul (c, &g, c)) != MP_OKAY) { mp_clear (&g); return res; } } /* shift to next bit */ b <<= 1; } mp_clear (&g); return MP_OKAY; } #endif /* \$Source\$ */ /* \$Revision: 0.41 \$ */ /* \$Date: 2007-04-18 09:58:18 +0000 \$ */ ``````