| lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame] | 1 | /* mpn_rshift -- Shift right a low-level natural-number integer. |
| 2 | |
| 3 | Copyright (C) 1991-2015 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 the GNU Lesser General Public License as published by |
| 9 | the Free Software Foundation; either version 2.1 of the License, or (at your |
| 10 | option) any later version. |
| 11 | |
| 12 | The GNU MP Library is distributed in the hope that it will be useful, but |
| 13 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
| 14 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
| 15 | License for more details. |
| 16 | |
| 17 | You should have received a copy of the GNU Lesser General Public License |
| 18 | along with the GNU MP Library; see the file COPYING.LIB. If not, see |
| 19 | <http://www.gnu.org/licenses/>. */ |
| 20 | |
| 21 | #include <gmp.h> |
| 22 | #include "gmp-impl.h" |
| 23 | |
| 24 | /* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right |
| 25 | and store the USIZE least significant limbs of the result at WP. |
| 26 | The bits shifted out to the right are returned. |
| 27 | |
| 28 | Argument constraints: |
| 29 | 1. 0 < CNT < BITS_PER_MP_LIMB |
| 30 | 2. If the result is to be written over the input, WP must be <= UP. |
| 31 | */ |
| 32 | |
| 33 | mp_limb_t |
| 34 | #if __STDC__ |
| 35 | mpn_rshift (register mp_ptr wp, |
| 36 | register mp_srcptr up, mp_size_t usize, |
| 37 | register unsigned int cnt) |
| 38 | #else |
| 39 | mpn_rshift (wp, up, usize, cnt) |
| 40 | register mp_ptr wp; |
| 41 | register mp_srcptr up; |
| 42 | mp_size_t usize; |
| 43 | register unsigned int cnt; |
| 44 | #endif |
| 45 | { |
| 46 | register mp_limb_t high_limb, low_limb; |
| 47 | register unsigned sh_1, sh_2; |
| 48 | register mp_size_t i; |
| 49 | mp_limb_t retval; |
| 50 | |
| 51 | #ifdef DEBUG |
| 52 | if (usize == 0 || cnt == 0) |
| 53 | abort (); |
| 54 | #endif |
| 55 | |
| 56 | sh_1 = cnt; |
| 57 | |
| 58 | #if 0 |
| 59 | if (sh_1 == 0) |
| 60 | { |
| 61 | if (wp != up) |
| 62 | { |
| 63 | /* Copy from low end to high end, to allow specified input/output |
| 64 | overlapping. */ |
| 65 | for (i = 0; i < usize; i++) |
| 66 | wp[i] = up[i]; |
| 67 | } |
| 68 | return usize; |
| 69 | } |
| 70 | #endif |
| 71 | |
| 72 | wp -= 1; |
| 73 | sh_2 = BITS_PER_MP_LIMB - sh_1; |
| 74 | high_limb = up[0]; |
| 75 | retval = high_limb << sh_2; |
| 76 | low_limb = high_limb; |
| 77 | |
| 78 | for (i = 1; i < usize; i++) |
| 79 | { |
| 80 | high_limb = up[i]; |
| 81 | wp[i] = (low_limb >> sh_1) | (high_limb << sh_2); |
| 82 | low_limb = high_limb; |
| 83 | } |
| 84 | wp[i] = low_limb >> sh_1; |
| 85 | |
| 86 | return retval; |
| 87 | } |