1/* mpz_cdiv_q_2exp, mpz_fdiv_q_2exp -- quotient from mpz divided by 2^n. 2 3Copyright 1991, 1993, 1994, 1996, 1998, 1999, 2001, 2002, 2004 Free Software 4Foundation, Inc. 5 6This file is part of the GNU MP Library. 7 8The GNU MP Library is free software; you can redistribute it and/or modify 9it under the terms of the GNU Lesser General Public License as published by 10the Free Software Foundation; either version 3 of the License, or (at your 11option) any later version. 12 13The GNU MP Library is distributed in the hope that it will be useful, but 14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 15or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 16License for more details. 17 18You should have received a copy of the GNU Lesser General Public License 19along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 20 21#include "gmp.h" 22#include "gmp-impl.h" 23 24 25/* dir==1 for ceil, dir==-1 for floor */ 26 27static void __gmpz_cfdiv_q_2exp __GMP_PROTO ((REGPARM_3_1 (mpz_ptr, mpz_srcptr, mp_bitcnt_t, int))) REGPARM_ATTR (1); 28#define cfdiv_q_2exp(w,u,cnt,dir) __gmpz_cfdiv_q_2exp (REGPARM_3_1 (w,u,cnt,dir)) 29 30REGPARM_ATTR (1) static void 31cfdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt, int dir) 32{ 33 mp_size_t wsize, usize, abs_usize, limb_cnt, i; 34 mp_srcptr up; 35 mp_ptr wp; 36 mp_limb_t round, rmask; 37 38 usize = SIZ (u); 39 abs_usize = ABS (usize); 40 limb_cnt = cnt / GMP_NUMB_BITS; 41 wsize = abs_usize - limb_cnt; 42 if (wsize <= 0) 43 { 44 /* u < 2**cnt, so result 1, 0 or -1 according to rounding */ 45 PTR(w)[0] = 1; 46 SIZ(w) = (usize == 0 || (usize ^ dir) < 0 ? 0 : dir); 47 return; 48 } 49 50 /* +1 limb to allow for mpn_add_1 below */ 51 MPZ_REALLOC (w, wsize+1); 52 53 /* Check for rounding if direction matches u sign. 54 Set round if we're skipping non-zero limbs. */ 55 up = PTR(u); 56 round = 0; 57 rmask = ((usize ^ dir) >= 0 ? MP_LIMB_T_MAX : 0); 58 if (rmask != 0) 59 for (i = 0; i < limb_cnt && round == 0; i++) 60 round = up[i]; 61 62 wp = PTR(w); 63 cnt %= GMP_NUMB_BITS; 64 if (cnt != 0) 65 { 66 round |= rmask & mpn_rshift (wp, up + limb_cnt, wsize, cnt); 67 wsize -= (wp[wsize - 1] == 0); 68 } 69 else 70 MPN_COPY_INCR (wp, up + limb_cnt, wsize); 71 72 if (round != 0) 73 { 74 if (wsize != 0) 75 { 76 mp_limb_t cy; 77 cy = mpn_add_1 (wp, wp, wsize, CNST_LIMB(1)); 78 wp[wsize] = cy; 79 wsize += cy; 80 } 81 else 82 { 83 /* We shifted something to zero. */ 84 wp[0] = 1; 85 wsize = 1; 86 } 87 } 88 SIZ(w) = (usize >= 0 ? wsize : -wsize); 89} 90 91 92void 93mpz_cdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt) 94{ 95 cfdiv_q_2exp (w, u, cnt, 1); 96} 97 98void 99mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt) 100{ 101 cfdiv_q_2exp (w, u, cnt, -1); 102} 103