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Diffstat (limited to 'libtommath/bn_mp_mod_2d.c')
-rw-r--r-- | libtommath/bn_mp_mod_2d.c | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/libtommath/bn_mp_mod_2d.c b/libtommath/bn_mp_mod_2d.c new file mode 100644 index 0000000..1e87a1d --- /dev/null +++ b/libtommath/bn_mp_mod_2d.c @@ -0,0 +1,55 @@ +#include <tommath.h> +#ifdef BN_MP_MOD_2D_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 + */ + +/* calc a value mod 2**b */ +int +mp_mod_2d (mp_int * a, int b, mp_int * c) +{ + int x, res; + + /* if b is <= 0 then zero the int */ + if (b <= 0) { + mp_zero (c); + return MP_OKAY; + } + + /* if the modulus is larger than the value than return */ + if (b >= (int) (a->used * DIGIT_BIT)) { + res = mp_copy (a, c); + return res; + } + + /* copy */ + if ((res = mp_copy (a, c)) != MP_OKAY) { + return res; + } + + /* zero digits above the last digit of the modulus */ + for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) { + c->dp[x] = 0; + } + /* clear the digit that is not completely outside/inside the modulus */ + c->dp[b / DIGIT_BIT] &= + (mp_digit) ((((mp_digit) 1) << (((mp_digit) b) % DIGIT_BIT)) - ((mp_digit) 1)); + mp_clamp (c); + return MP_OKAY; +} +#endif + +/* $Source: /root/tcl/repos-to-convert/tcl/libtommath/bn_mp_mod_2d.c,v $ */ +/* $Revision: 1.1.1.1.2.1 $ */ +/* $Date: 2005/09/26 20:16:53 $ */ |