diff options
Diffstat (limited to '')
-rw-r--r-- | third_party/heimdal/lib/hcrypto/libtommath/bn_mp_gcd.c | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_gcd.c b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_gcd.c new file mode 100644 index 0000000..53029ba --- /dev/null +++ b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_gcd.c @@ -0,0 +1,92 @@ +#include "tommath_private.h" +#ifdef BN_MP_GCD_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis */ +/* SPDX-License-Identifier: Unlicense */ + +/* Greatest Common Divisor using the binary method */ +mp_err mp_gcd(const mp_int *a, const mp_int *b, mp_int *c) +{ + mp_int u, v; + int k, u_lsb, v_lsb; + mp_err err; + + /* either zero than gcd is the largest */ + if (MP_IS_ZERO(a)) { + return mp_abs(b, c); + } + if (MP_IS_ZERO(b)) { + return mp_abs(a, c); + } + + /* get copies of a and b we can modify */ + if ((err = mp_init_copy(&u, a)) != MP_OKAY) { + return err; + } + + if ((err = mp_init_copy(&v, b)) != MP_OKAY) { + goto LBL_U; + } + + /* must be positive for the remainder of the algorithm */ + u.sign = v.sign = MP_ZPOS; + + /* B1. Find the common power of two for u and v */ + u_lsb = mp_cnt_lsb(&u); + v_lsb = mp_cnt_lsb(&v); + k = MP_MIN(u_lsb, v_lsb); + + if (k > 0) { + /* divide the power of two out */ + if ((err = mp_div_2d(&u, k, &u, NULL)) != MP_OKAY) { + goto LBL_V; + } + + if ((err = mp_div_2d(&v, k, &v, NULL)) != MP_OKAY) { + goto LBL_V; + } + } + + /* divide any remaining factors of two out */ + if (u_lsb != k) { + if ((err = mp_div_2d(&u, u_lsb - k, &u, NULL)) != MP_OKAY) { + goto LBL_V; + } + } + + if (v_lsb != k) { + if ((err = mp_div_2d(&v, v_lsb - k, &v, NULL)) != MP_OKAY) { + goto LBL_V; + } + } + + while (!MP_IS_ZERO(&v)) { + /* make sure v is the largest */ + if (mp_cmp_mag(&u, &v) == MP_GT) { + /* swap u and v to make sure v is >= u */ + mp_exch(&u, &v); + } + + /* subtract smallest from largest */ + if ((err = s_mp_sub(&v, &u, &v)) != MP_OKAY) { + goto LBL_V; + } + + /* Divide out all factors of two */ + if ((err = mp_div_2d(&v, mp_cnt_lsb(&v), &v, NULL)) != MP_OKAY) { + goto LBL_V; + } + } + + /* multiply by 2**k which we divided out at the beginning */ + if ((err = mp_mul_2d(&u, k, c)) != MP_OKAY) { + goto LBL_V; + } + c->sign = MP_ZPOS; + err = MP_OKAY; +LBL_V: + mp_clear(&u); +LBL_U: + mp_clear(&v); + return err; +} +#endif |