1 /* mpz_cdiv_r_2exp, mpz_fdiv_r_2exp -- remainder from mpz divided by 2^n. 2 3 Copyright 2001, 2002, 2004, 2012 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.h" 32 #include "gmp-impl.h" 33 34 35 /* Bit mask of "n" least significant bits of a limb. */ 36 #define LOW_MASK(n) ((CNST_LIMB(1) << (n)) - 1) 37 38 39 /* dir==1 for ceil, dir==-1 for floor */ 40 41 static void __gmpz_cfdiv_r_2exp (REGPARM_3_1 (mpz_ptr, mpz_srcptr, mp_bitcnt_t, int)) REGPARM_ATTR (1); 42 #define cfdiv_r_2exp(w,u,cnt,dir) __gmpz_cfdiv_r_2exp (REGPARM_3_1 (w, u, cnt, dir)) 43 44 REGPARM_ATTR (1) static void 45 cfdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt, int dir) 46 { 47 mp_size_t usize, abs_usize, limb_cnt, i; 48 mp_srcptr up; 49 mp_ptr wp; 50 mp_limb_t high; 51 52 usize = SIZ(u); 53 if (usize == 0) 54 { 55 SIZ(w) = 0; 56 return; 57 } 58 59 limb_cnt = cnt / GMP_NUMB_BITS; 60 cnt %= GMP_NUMB_BITS; 61 abs_usize = ABS (usize); 62 63 /* MPZ_REALLOC(w) below is only when w!=u, so we can fetch PTR(u) here 64 nice and early */ 65 up = PTR(u); 66 67 if ((usize ^ dir) < 0) 68 { 69 /* Round towards zero, means just truncate */ 70 71 if (w == u) 72 { 73 /* if already smaller than limb_cnt then do nothing */ 74 if (abs_usize <= limb_cnt) 75 return; 76 wp = (mp_ptr) up; 77 } 78 else 79 { 80 i = MIN (abs_usize, limb_cnt+1); 81 wp = MPZ_NEWALLOC (w, i); 82 MPN_COPY (wp, up, i); 83 84 /* if smaller than limb_cnt then only the copy is needed */ 85 if (abs_usize <= limb_cnt) 86 { 87 SIZ(w) = usize; 88 return; 89 } 90 } 91 } 92 else 93 { 94 /* Round away from zero, means twos complement if non-zero */ 95 96 /* if u!=0 and smaller than divisor, then must negate */ 97 if (abs_usize <= limb_cnt) 98 goto negate; 99 100 /* if non-zero low limb, then must negate */ 101 for (i = 0; i < limb_cnt; i++) 102 if (up[i] != 0) 103 goto negate; 104 105 /* if non-zero partial limb, then must negate */ 106 if ((up[limb_cnt] & LOW_MASK (cnt)) != 0) 107 goto negate; 108 109 /* otherwise low bits of u are zero, so that's the result */ 110 SIZ(w) = 0; 111 return; 112 113 negate: 114 /* twos complement negation to get 2**cnt-u */ 115 116 wp = MPZ_REALLOC (w, limb_cnt+1); 117 up = PTR(u); 118 119 /* Ones complement */ 120 i = MIN (abs_usize, limb_cnt+1); 121 ASSERT_CARRY (mpn_neg (wp, up, i)); 122 for ( ; i <= limb_cnt; i++) 123 wp[i] = GMP_NUMB_MAX; 124 125 usize = -usize; 126 } 127 128 /* Mask the high limb */ 129 high = wp[limb_cnt]; 130 high &= LOW_MASK (cnt); 131 wp[limb_cnt] = high; 132 133 /* Strip any consequent high zeros */ 134 while (high == 0) 135 { 136 limb_cnt--; 137 if (limb_cnt < 0) 138 { 139 SIZ(w) = 0; 140 return; 141 } 142 high = wp[limb_cnt]; 143 } 144 145 limb_cnt++; 146 SIZ(w) = (usize >= 0 ? limb_cnt : -limb_cnt); 147 } 148 149 150 void 151 mpz_cdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt) 152 { 153 cfdiv_r_2exp (w, u, cnt, 1); 154 } 155 156 void 157 mpz_fdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt) 158 { 159 cfdiv_r_2exp (w, u, cnt, -1); 160 } 161