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author | Kevin B Kenny <kennykb@acm.org> | 2005-01-19 22:41:26 (GMT) |
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committer | Kevin B Kenny <kennykb@acm.org> | 2005-01-19 22:41:26 (GMT) |
commit | ef78ca64ce6ba6a8786f083318fe536f2bd52925 (patch) | |
tree | 47f8ad0d7291237c7f9af988c5e05275ed9286ee /libtommath/bn_mp_expt_d.c | |
parent | b23d942a1e86ddee18c2309afd7fa7e9afa79ef8 (diff) | |
download | tcl-ef78ca64ce6ba6a8786f083318fe536f2bd52925.zip tcl-ef78ca64ce6ba6a8786f083318fe536f2bd52925.tar.gz tcl-ef78ca64ce6ba6a8786f083318fe536f2bd52925.tar.bz2 |
Import of libtommath 0.33
Diffstat (limited to 'libtommath/bn_mp_expt_d.c')
-rw-r--r-- | libtommath/bn_mp_expt_d.c | 53 |
1 files changed, 53 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..fdb8bd9 --- /dev/null +++ b/libtommath/bn_mp_expt_d.c @@ -0,0 +1,53 @@ +#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 |