1 /* mpf_div -- Divide two floats. 2 3 Copyright 1993, 1994, 1996, 2000, 2001, 2002, 2004, 2005, 2010 Free Software 4 Foundation, Inc. 5 6 This file is part of the GNU MP Library. 7 8 The GNU MP Library is free software; you can redistribute it and/or modify 9 it under the terms of the GNU Lesser General Public License as published by 10 the Free Software Foundation; either version 3 of the License, or (at your 11 option) any later version. 12 13 The GNU MP Library is distributed in the hope that it will be useful, but 14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 16 License for more details. 17 18 You should have received a copy of the GNU Lesser General Public License 19 along 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 /* Not done: 26 27 No attempt is made to identify an overlap u==v. The result will be 28 correct (1.0), but a full actual division is done whereas of course 29 x/x==1 needs no work. Such a call is not a sensible thing to make, and 30 it's left to an application to notice and optimize if it might arise 31 somehow through pointer aliasing or whatever. 32 33 Enhancements: 34 35 The high quotient limb is non-zero when high{up,vsize} >= {vp,vsize}. We 36 could make that comparison and use qsize==prec instead of qsize==prec+1, 37 to save one limb in the division. 38 39 If r==u but the size is enough bigger than prec that there won't be an 40 overlap between quotient and dividend in mpn_tdiv_qr, then we can avoid 41 copying up,usize. This would only arise from a prec reduced with 42 mpf_set_prec_raw and will be pretty unusual, but might be worthwhile if 43 it could be worked into the copy_u decision cleanly. */ 44 45 void 46 mpf_div (mpf_ptr r, mpf_srcptr u, mpf_srcptr v) 47 { 48 mp_srcptr up, vp; 49 mp_ptr rp, tp, new_vp; 50 mp_size_t usize, vsize, rsize, prospective_rsize, tsize, zeros; 51 mp_size_t sign_quotient, prec, high_zero, chop; 52 mp_exp_t rexp; 53 int copy_u; 54 TMP_DECL; 55 56 usize = SIZ(u); 57 vsize = SIZ(v); 58 sign_quotient = usize ^ vsize; 59 usize = ABS (usize); 60 vsize = ABS (vsize); 61 prec = PREC(r); 62 63 if (vsize == 0) 64 DIVIDE_BY_ZERO; 65 66 if (usize == 0) 67 { 68 SIZ(r) = 0; 69 EXP(r) = 0; 70 return; 71 } 72 73 TMP_MARK; 74 rexp = EXP(u) - EXP(v) + 1; 75 76 rp = PTR(r); 77 up = PTR(u); 78 vp = PTR(v); 79 80 prospective_rsize = usize - vsize + 1; /* quot from using given u,v sizes */ 81 rsize = prec + 1; /* desired quot */ 82 83 zeros = rsize - prospective_rsize; /* padding u to give rsize */ 84 copy_u = (zeros > 0 || rp == up); /* copy u if overlap or padding */ 85 86 chop = MAX (-zeros, 0); /* negative zeros means shorten u */ 87 up += chop; 88 usize -= chop; 89 zeros += chop; /* now zeros >= 0 */ 90 91 tsize = usize + zeros; /* size for possible copy of u */ 92 93 /* copy and possibly extend u if necessary */ 94 if (copy_u) 95 { 96 tp = TMP_ALLOC_LIMBS (tsize + 1); /* +1 for mpn_div_q's scratch needs */ 97 MPN_ZERO (tp, zeros); 98 MPN_COPY (tp+zeros, up, usize); 99 up = tp; 100 usize = tsize; 101 } 102 else 103 { 104 tp = TMP_ALLOC_LIMBS (usize + 1); 105 } 106 107 /* ensure divisor doesn't overlap quotient */ 108 if (rp == vp) 109 { 110 new_vp = TMP_ALLOC_LIMBS (vsize); 111 MPN_COPY (new_vp, vp, vsize); 112 vp = new_vp; 113 } 114 115 ASSERT (usize-vsize+1 == rsize); 116 mpn_div_q (rp, up, usize, vp, vsize, tp); 117 118 /* strip possible zero high limb */ 119 high_zero = (rp[rsize-1] == 0); 120 rsize -= high_zero; 121 rexp -= high_zero; 122 123 SIZ(r) = sign_quotient >= 0 ? rsize : -rsize; 124 EXP(r) = rexp; 125 TMP_FREE; 126 } 127