diff options
Diffstat (limited to 'third_party/heimdal/lib/hcrypto/libtommath/bn_mp_sqrt.c')
-rw-r--r-- | third_party/heimdal/lib/hcrypto/libtommath/bn_mp_sqrt.c | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_sqrt.c b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_sqrt.c new file mode 100644 index 0000000..82d6824 --- /dev/null +++ b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_sqrt.c @@ -0,0 +1,67 @@ +#include "tommath_private.h" +#ifdef BN_MP_SQRT_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis */ +/* SPDX-License-Identifier: Unlicense */ + +/* this function is less generic than mp_n_root, simpler and faster */ +mp_err mp_sqrt(const mp_int *arg, mp_int *ret) +{ + mp_err err; + mp_int t1, t2; + + /* must be positive */ + if (arg->sign == MP_NEG) { + return MP_VAL; + } + + /* easy out */ + if (MP_IS_ZERO(arg)) { + mp_zero(ret); + return MP_OKAY; + } + + if ((err = mp_init_copy(&t1, arg)) != MP_OKAY) { + return err; + } + + if ((err = mp_init(&t2)) != MP_OKAY) { + goto E2; + } + + /* First approx. (not very bad for large arg) */ + mp_rshd(&t1, t1.used/2); + + /* t1 > 0 */ + if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) { + goto E1; + } + if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) { + goto E1; + } + if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) { + goto E1; + } + /* And now t1 > sqrt(arg) */ + do { + if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) { + goto E1; + } + if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) { + goto E1; + } + if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) { + goto E1; + } + /* t1 >= sqrt(arg) >= t2 at this point */ + } while (mp_cmp_mag(&t1, &t2) == MP_GT); + + mp_exch(&t1, ret); + +E1: + mp_clear(&t2); +E2: + mp_clear(&t1); + return err; +} + +#endif |