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Diffstat (limited to 'libtommath/bn_mp_div_2.c')
-rw-r--r-- | libtommath/bn_mp_div_2.c | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/libtommath/bn_mp_div_2.c b/libtommath/bn_mp_div_2.c new file mode 100644 index 0000000..b3a9669 --- /dev/null +++ b/libtommath/bn_mp_div_2.c @@ -0,0 +1,68 @@ +#include <tommath.h> +#ifdef BN_MP_DIV_2_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 + */ + +/* b = a/2 */ +int mp_div_2(mp_int * a, mp_int * b) +{ + int x, res, oldused; + + /* copy */ + if (b->alloc < a->used) { + if ((res = mp_grow (b, a->used)) != MP_OKAY) { + return res; + } + } + + oldused = b->used; + b->used = a->used; + { + register mp_digit r, rr, *tmpa, *tmpb; + + /* source alias */ + tmpa = a->dp + b->used - 1; + + /* dest alias */ + tmpb = b->dp + b->used - 1; + + /* carry */ + r = 0; + for (x = b->used - 1; x >= 0; x--) { + /* get the carry for the next iteration */ + rr = *tmpa & 1; + + /* shift the current digit, add in carry and store */ + *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1)); + + /* forward carry to next iteration */ + r = rr; + } + + /* zero excess digits */ + tmpb = b->dp + b->used; + for (x = b->used; x < oldused; x++) { + *tmpb++ = 0; + } + } + b->sign = a->sign; + mp_clamp (b); + return MP_OKAY; +} +#endif + +/* $Source: /root/tcl/repos-to-convert/tcl/libtommath/bn_mp_div_2.c,v $ */ +/* $Revision: 1.1.1.1.2.1 $ */ +/* $Date: 2005/09/26 20:16:53 $ */ |