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Diffstat (limited to 'libtommath/bn_mp_expt_d.c')
-rw-r--r-- | libtommath/bn_mp_expt_d.c | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/libtommath/bn_mp_expt_d.c b/libtommath/bn_mp_expt_d.c new file mode 100644 index 0000000..2fc1484 --- /dev/null +++ b/libtommath/bn_mp_expt_d.c @@ -0,0 +1,57 @@ +#include <tommath.h> +#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@iahu.ca, http://math.libtomcrypt.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: /root/tcl/repos-to-convert/tcl/libtommath/bn_mp_expt_d.c,v $ */ +/* $Revision: 1.1.1.1.2.1 $ */ +/* $Date: 2005/09/26 20:16:53 $ */ |