diff options
Diffstat (limited to 'third_party/heimdal/lib/hcrypto/libtommath/bn_mp_div_2.c')
-rw-r--r-- | third_party/heimdal/lib/hcrypto/libtommath/bn_mp_div_2.c | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_div_2.c b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_div_2.c new file mode 100644 index 0000000..f56ea81 --- /dev/null +++ b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_div_2.c @@ -0,0 +1,49 @@ +#include "tommath_private.h" +#ifdef BN_MP_DIV_2_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis */ +/* SPDX-License-Identifier: Unlicense */ + +/* b = a/2 */ +mp_err mp_div_2(const mp_int *a, mp_int *b) +{ + int x, oldused; + mp_digit r, rr, *tmpa, *tmpb; + mp_err err; + + /* copy */ + if (b->alloc < a->used) { + if ((err = mp_grow(b, a->used)) != MP_OKAY) { + return err; + } + } + + oldused = b->used; + b->used = a->used; + + /* 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 & 1u; + + /* shift the current digit, add in carry and store */ + *tmpb-- = (*tmpa-- >> 1) | (r << (MP_DIGIT_BIT - 1)); + + /* forward carry to next iteration */ + r = rr; + } + + /* zero excess digits */ + MP_ZERO_DIGITS(b->dp + b->used, oldused - b->used); + + b->sign = a->sign; + mp_clamp(b); + return MP_OKAY; +} +#endif |