| Austin Schuh | dace2a6 | 2020-08-18 10:56:48 -0700 | [diff] [blame^] | 1 | /* mpn_scan0 -- Scan from a given bit position for the next clear bit. |
| 2 | |
| 3 | Copyright 1994, 1996, 2001, 2002, 2004 Free Software Foundation, Inc. |
| 4 | |
| 5 | This file is part of the GNU MP Library. |
| 6 | |
| 7 | The GNU MP Library is free software; you can redistribute it and/or modify |
| 8 | it under the terms of either: |
| 9 | |
| 10 | * the GNU Lesser General Public License as published by the Free |
| 11 | Software Foundation; either version 3 of the License, or (at your |
| 12 | option) any later version. |
| 13 | |
| 14 | or |
| 15 | |
| 16 | * the GNU General Public License as published by the Free Software |
| 17 | Foundation; either version 2 of the License, or (at your option) any |
| 18 | later version. |
| 19 | |
| 20 | or both in parallel, as here. |
| 21 | |
| 22 | The GNU MP Library is distributed in the hope that it will be useful, but |
| 23 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
| 24 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 25 | for more details. |
| 26 | |
| 27 | You should have received copies of the GNU General Public License and the |
| 28 | GNU Lesser General Public License along with the GNU MP Library. If not, |
| 29 | see https://www.gnu.org/licenses/. */ |
| 30 | |
| 31 | #include "gmp-impl.h" |
| 32 | #include "longlong.h" |
| 33 | |
| 34 | /* Argument constraints: |
| 35 | 1. U must sooner or later have a limb with a clear bit. |
| 36 | */ |
| 37 | |
| 38 | mp_bitcnt_t |
| 39 | mpn_scan0 (mp_srcptr up, mp_bitcnt_t starting_bit) |
| 40 | { |
| 41 | mp_size_t starting_word; |
| 42 | mp_limb_t alimb; |
| 43 | int cnt; |
| 44 | mp_srcptr p; |
| 45 | |
| 46 | /* Start at the word implied by STARTING_BIT. */ |
| 47 | starting_word = starting_bit / GMP_NUMB_BITS; |
| 48 | p = up + starting_word; |
| 49 | alimb = *p++ ^ GMP_NUMB_MASK; |
| 50 | |
| 51 | /* Mask off any bits before STARTING_BIT in the first limb. */ |
| 52 | alimb &= - (mp_limb_t) 1 << (starting_bit % GMP_NUMB_BITS); |
| 53 | |
| 54 | while (alimb == 0) |
| 55 | alimb = *p++ ^ GMP_NUMB_MASK; |
| 56 | |
| 57 | count_trailing_zeros (cnt, alimb); |
| 58 | return (p - up - 1) * GMP_NUMB_BITS + cnt; |
| 59 | } |