| Austin Schuh | bb1338c | 2024-06-15 19:31:16 -0700 | [diff] [blame] | 1 | /* mpn_rshift -- Shift right low level. |
| 2 | |
| 3 | Copyright 1991, 1993, 1994, 1996, 2000-2002 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 | |
| 33 | /* Shift U (pointed to by up and N limbs long) cnt bits to the right |
| 34 | and store the n least significant limbs of the result at rp. |
| 35 | The bits shifted out to the right are returned. |
| 36 | |
| 37 | Argument constraints: |
| 38 | 1. 0 < cnt < GMP_NUMB_BITS. |
| 39 | 2. If the result is to be written over the input, rp must be <= up. |
| 40 | */ |
| 41 | |
| 42 | mp_limb_t |
| 43 | mpn_rshift (mp_ptr rp, mp_srcptr up, mp_size_t n, unsigned int cnt) |
| 44 | { |
| 45 | mp_limb_t high_limb, low_limb; |
| 46 | unsigned int tnc; |
| 47 | mp_size_t i; |
| 48 | mp_limb_t retval; |
| 49 | |
| 50 | ASSERT (n >= 1); |
| 51 | ASSERT (cnt >= 1); |
| 52 | ASSERT (cnt < GMP_NUMB_BITS); |
| 53 | ASSERT (MPN_SAME_OR_INCR_P (rp, up, n)); |
| 54 | |
| 55 | tnc = GMP_NUMB_BITS - cnt; |
| 56 | high_limb = *up++; |
| 57 | retval = (high_limb << tnc) & GMP_NUMB_MASK; |
| 58 | low_limb = high_limb >> cnt; |
| 59 | |
| 60 | for (i = n - 1; i != 0; i--) |
| 61 | { |
| 62 | high_limb = *up++; |
| 63 | *rp++ = low_limb | ((high_limb << tnc) & GMP_NUMB_MASK); |
| 64 | low_limb = high_limb >> cnt; |
| 65 | } |
| 66 | *rp = low_limb; |
| 67 | |
| 68 | return retval; |
| 69 | } |