diff options
Diffstat (limited to 'vendor/gmp-6.3.0/mpz/scan1.c')
| -rw-r--r-- | vendor/gmp-6.3.0/mpz/scan1.c | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/vendor/gmp-6.3.0/mpz/scan1.c b/vendor/gmp-6.3.0/mpz/scan1.c new file mode 100644 index 0000000..d096147 --- /dev/null +++ b/vendor/gmp-6.3.0/mpz/scan1.c @@ -0,0 +1,123 @@ +/* mpz_scan1 -- search for a 1 bit. + +Copyright 2000-2002, 2004, 2012, 2015 Free Software Foundation, Inc. + +This file is part of the GNU MP Library. + +The GNU MP Library is free software; you can redistribute it and/or modify +it under the terms of either: + + * the GNU Lesser General Public License as published by the Free + Software Foundation; either version 3 of the License, or (at your + option) any later version. + +or + + * the GNU General Public License as published by the Free Software + Foundation; either version 2 of the License, or (at your option) any + later version. + +or both in parallel, as here. + +The GNU MP Library is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY +or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License +for more details. + +You should have received copies of the GNU General Public License and the +GNU Lesser General Public License along with the GNU MP Library. If not, +see https://www.gnu.org/licenses/. */ + +#include "gmp-impl.h" +#include "longlong.h" + + +/* mpn_scan0 can't be used for the inverted u<0 search since there might not + be a 0 bit before the end of the data. mpn_scan1 could be used under u>0 + (except when in the high limb), but usually the search won't go very far + so it seems reasonable to inline that code. */ + +mp_bitcnt_t +mpz_scan1 (mpz_srcptr u, mp_bitcnt_t starting_bit) __GMP_NOTHROW +{ + mp_srcptr u_ptr = PTR(u); + mp_size_t size = SIZ(u); + mp_size_t abs_size = ABS(size); + mp_srcptr u_end = u_ptr + abs_size - 1; + mp_size_t starting_limb = starting_bit / GMP_NUMB_BITS; + mp_srcptr p = u_ptr + starting_limb; + mp_limb_t limb; + int cnt; + + /* Past the end there's no 1 bits for u>=0, or an immediate 1 bit for u<0. + Notice this test picks up any u==0 too. */ + if (starting_limb >= abs_size) + return (size >= 0 ? ~(mp_bitcnt_t) 0 : starting_bit); + + /* This is an important case, where sign is not relevant! */ + if (starting_bit == 0) + goto short_cut; + + limb = *p; + + if (size >= 0) + { + /* Mask to 0 all bits before starting_bit, thus ignoring them. */ + limb &= (MP_LIMB_T_MAX << (starting_bit % GMP_NUMB_BITS)); + + if (limb == 0) + { + /* If it's the high limb which is zero after masking, then there's + no 1 bits after starting_bit. */ + if (p == u_end) + return ~(mp_bitcnt_t) 0; + + /* Otherwise search further for a non-zero limb. The high limb is + non-zero, if nothing else. */ + search_nonzero: + do + { + ASSERT (p != u_end); + p++; + short_cut: + limb = *p; + } + while (limb == 0); + } + } + else + { + /* If there's a non-zero limb before ours then we're in the ones + complement region. */ + if (starting_limb == 0 || mpn_zero_p (u_ptr, starting_limb)) { + if (limb == 0) + /* Seeking for the first non-zero bit, it is the same for u and -u. */ + goto search_nonzero; + + /* Adjust so ~limb implied by searching for 0 bit becomes -limb. */ + limb--; + } + + /* Now seeking a 0 bit. */ + + /* Mask to 1 all bits before starting_bit, thus ignoring them. */ + limb |= (CNST_LIMB(1) << (starting_bit % GMP_NUMB_BITS)) - 1; + + /* Search for a limb which is not all ones. If the end is reached + then the zero immediately past the end is the result. */ + while (limb == GMP_NUMB_MAX) + { + if (p == u_end) + return (mp_bitcnt_t) abs_size * GMP_NUMB_BITS; + p++; + limb = *p; + } + + /* Now seeking low 1 bit. */ + limb = ~limb; + } + + ASSERT (limb != 0); + count_trailing_zeros (cnt, limb); + return (mp_bitcnt_t) (p - u_ptr) * GMP_NUMB_BITS + cnt; +} |