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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_montgomery_calc_normalization.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_montgomery_calc_normalization.c')
-rw-r--r-- | libtommath/bn_mp_montgomery_calc_normalization.c | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/libtommath/bn_mp_montgomery_calc_normalization.c b/libtommath/bn_mp_montgomery_calc_normalization.c new file mode 100644 index 0000000..0a760cf --- /dev/null +++ b/libtommath/bn_mp_montgomery_calc_normalization.c @@ -0,0 +1,56 @@ +#include <tommath.h> +#ifdef BN_MP_MONTGOMERY_CALC_NORMALIZATION_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 + */ + +/* + * shifts with subtractions when the result is greater than b. + * + * The method is slightly modified to shift B unconditionally upto just under + * the leading bit of b. This saves alot of multiple precision shifting. + */ +int mp_montgomery_calc_normalization (mp_int * a, mp_int * b) +{ + int x, bits, res; + + /* how many bits of last digit does b use */ + bits = mp_count_bits (b) % DIGIT_BIT; + + + if (b->used > 1) { + if ((res = mp_2expt (a, (b->used - 1) * DIGIT_BIT + bits - 1)) != MP_OKAY) { + return res; + } + } else { + mp_set(a, 1); + bits = 1; + } + + + /* now compute C = A * B mod b */ + for (x = bits - 1; x < (int)DIGIT_BIT; x++) { + if ((res = mp_mul_2 (a, a)) != MP_OKAY) { + return res; + } + if (mp_cmp_mag (a, b) != MP_LT) { + if ((res = s_mp_sub (a, b, a)) != MP_OKAY) { + return res; + } + } + } + + return MP_OKAY; +} +#endif |