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author | jan.nijtmans <nijtmans@users.sourceforge.net> | 2016-11-16 13:04:26 (GMT) |
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committer | jan.nijtmans <nijtmans@users.sourceforge.net> | 2016-11-16 13:04:26 (GMT) |
commit | 2adcff3e5ba6e09366ef4208ab81768803ba15bd (patch) | |
tree | 963ed4c25de0f3f0b60d2392c5fd0e7441e548e5 /libtommath/bn_mp_expt_d_ex.c | |
parent | fac003f85aeba679d1cc6bea4eb8a84fc0ebd9f0 (diff) | |
download | tcl-2adcff3e5ba6e09366ef4208ab81768803ba15bd.zip tcl-2adcff3e5ba6e09366ef4208ab81768803ba15bd.tar.gz tcl-2adcff3e5ba6e09366ef4208ab81768803ba15bd.tar.bz2 |
import libtommath 1.0
Diffstat (limited to 'libtommath/bn_mp_expt_d_ex.c')
-rw-r--r-- | libtommath/bn_mp_expt_d_ex.c | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/libtommath/bn_mp_expt_d_ex.c b/libtommath/bn_mp_expt_d_ex.c new file mode 100644 index 0000000..649d224 --- /dev/null +++ b/libtommath/bn_mp_expt_d_ex.c @@ -0,0 +1,83 @@ +#include <tommath_private.h> +#ifdef BN_MP_EXPT_D_EX_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, tstdenis82@gmail.com, http://libtom.org + */ + +/* calculate c = a**b using a square-multiply algorithm */ +int mp_expt_d_ex (mp_int * a, mp_digit b, mp_int * c, int fast) +{ + int res; + unsigned int x; + + mp_int g; + + if ((res = mp_init_copy (&g, a)) != MP_OKAY) { + return res; + } + + /* set initial result */ + mp_set (c, 1); + + if (fast != 0) { + while (b > 0) { + /* if the bit is set multiply */ + if ((b & 1) != 0) { + if ((res = mp_mul (c, &g, c)) != MP_OKAY) { + mp_clear (&g); + return res; + } + } + + /* square */ + if (b > 1) { + if ((res = mp_sqr (&g, &g)) != MP_OKAY) { + mp_clear (&g); + return res; + } + } + + /* shift to next bit */ + b >>= 1; + } + } + else { + for (x = 0; x < 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; + } + } /* if ... else */ + + mp_clear (&g); + return MP_OKAY; +} +#endif + +/* $Source$ */ +/* $Revision$ */ +/* $Date$ */ |