diff options
Diffstat (limited to 'libtommath/bn_mp_expt_d_ex.c')
-rw-r--r-- | libtommath/bn_mp_expt_d_ex.c | 82 |
1 files changed, 82 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..99319a5 --- /dev/null +++ b/libtommath/bn_mp_expt_d_ex.c @@ -0,0 +1,82 @@ +#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(const 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 + +/* ref: $Format:%D$ */ +/* git commit: $Format:%H$ */ +/* commit time: $Format:%ai$ */ |