From 11da511c784eca003deb90c23570f0873954e0de Mon Sep 17 00:00:00 2001 From: Duncan Wilkie Date: Sat, 18 Nov 2023 06:11:09 -0600 Subject: Initial commit. --- gmp-6.3.0/mpz/tstbit.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 80 insertions(+) create mode 100644 gmp-6.3.0/mpz/tstbit.c (limited to 'gmp-6.3.0/mpz/tstbit.c') diff --git a/gmp-6.3.0/mpz/tstbit.c b/gmp-6.3.0/mpz/tstbit.c new file mode 100644 index 0000000..48725d4 --- /dev/null +++ b/gmp-6.3.0/mpz/tstbit.c @@ -0,0 +1,80 @@ +/* mpz_tstbit -- test a specified bit. + +Copyright 2000, 2002 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" + + +/* For negatives the effective twos complement is achieved by negating the + limb tested, either with a ones or twos complement. Twos complement + ("-") is used if there's only zero limbs below the one being tested. + Ones complement ("~") is used if there's a non-zero below. Note that "-" + is correct even if the limb examined is 0 (and the true beginning of twos + complement is further up). + + Testing the limbs below p is unavoidable on negatives, but will usually + need to examine only *(p-1). The search is done from *(p-1) down to + *u_ptr, since that might give better cache locality, and because a + non-zero limb is perhaps a touch more likely in the middle of a number + than at the low end. + + Bits past the end of available data simply follow sign of u. Notice that + the limb_index >= abs_size test covers u=0 too. */ + +int +mpz_tstbit (mpz_srcptr u, mp_bitcnt_t bit_index) __GMP_NOTHROW +{ + mp_srcptr u_ptr = PTR(u); + mp_size_t size = SIZ(u); + unsigned abs_size = ABS(size); + mp_size_t limb_index = bit_index / GMP_NUMB_BITS; + mp_srcptr p = u_ptr + limb_index; + mp_limb_t limb; + + if (limb_index >= abs_size) + return (size < 0); + + limb = *p; + if (size < 0) + { + limb = -limb; /* twos complement */ + + while (p != u_ptr) + { + p--; + if (*p != 0) + { + limb--; /* make it a ones complement instead */ + break; + } + } + } + + return (limb >> (bit_index % GMP_NUMB_BITS)) & 1; +} -- cgit v1.2.3