1 /* mpz/gcd.c: Calculate the greatest common divisor of two integers. 2 3 Copyright 1991, 1993, 1994, 1996, 2000, 2001, 2002, 2005, 2010 Free 4 Software 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 #include "longlong.h" 24 25 26 void 27 mpz_gcd (mpz_ptr g, mpz_srcptr u, mpz_srcptr v) 28 { 29 unsigned long int g_zero_bits, u_zero_bits, v_zero_bits; 30 mp_size_t g_zero_limbs, u_zero_limbs, v_zero_limbs; 31 mp_ptr tp; 32 mp_ptr up; 33 mp_size_t usize; 34 mp_ptr vp; 35 mp_size_t vsize; 36 mp_size_t gsize; 37 TMP_DECL; 38 39 up = PTR(u); 40 usize = ABSIZ (u); 41 vp = PTR(v); 42 vsize = ABSIZ (v); 43 /* GCD(0, V) == V. */ 44 if (usize == 0) 45 { 46 SIZ (g) = vsize; 47 if (g == v) 48 return; 49 MPZ_REALLOC (g, vsize); 50 MPN_COPY (PTR (g), vp, vsize); 51 return; 52 } 53 54 /* GCD(U, 0) == U. */ 55 if (vsize == 0) 56 { 57 SIZ (g) = usize; 58 if (g == u) 59 return; 60 MPZ_REALLOC (g, usize); 61 MPN_COPY (PTR (g), up, usize); 62 return; 63 } 64 65 if (usize == 1) 66 { 67 SIZ (g) = 1; 68 PTR (g)[0] = mpn_gcd_1 (vp, vsize, up[0]); 69 return; 70 } 71 72 if (vsize == 1) 73 { 74 SIZ(g) = 1; 75 PTR (g)[0] = mpn_gcd_1 (up, usize, vp[0]); 76 return; 77 } 78 79 TMP_MARK; 80 81 /* Eliminate low zero bits from U and V and move to temporary storage. */ 82 while (*up == 0) 83 up++; 84 u_zero_limbs = up - PTR(u); 85 usize -= u_zero_limbs; 86 count_trailing_zeros (u_zero_bits, *up); 87 tp = up; 88 up = TMP_ALLOC_LIMBS (usize); 89 if (u_zero_bits != 0) 90 { 91 mpn_rshift (up, tp, usize, u_zero_bits); 92 usize -= up[usize - 1] == 0; 93 } 94 else 95 MPN_COPY (up, tp, usize); 96 97 while (*vp == 0) 98 vp++; 99 v_zero_limbs = vp - PTR (v); 100 vsize -= v_zero_limbs; 101 count_trailing_zeros (v_zero_bits, *vp); 102 tp = vp; 103 vp = TMP_ALLOC_LIMBS (vsize); 104 if (v_zero_bits != 0) 105 { 106 mpn_rshift (vp, tp, vsize, v_zero_bits); 107 vsize -= vp[vsize - 1] == 0; 108 } 109 else 110 MPN_COPY (vp, tp, vsize); 111 112 if (u_zero_limbs > v_zero_limbs) 113 { 114 g_zero_limbs = v_zero_limbs; 115 g_zero_bits = v_zero_bits; 116 } 117 else if (u_zero_limbs < v_zero_limbs) 118 { 119 g_zero_limbs = u_zero_limbs; 120 g_zero_bits = u_zero_bits; 121 } 122 else /* Equal. */ 123 { 124 g_zero_limbs = u_zero_limbs; 125 g_zero_bits = MIN (u_zero_bits, v_zero_bits); 126 } 127 128 /* Call mpn_gcd. The 2nd argument must not have more bits than the 1st. */ 129 vsize = (usize < vsize || (usize == vsize && up[usize-1] < vp[vsize-1])) 130 ? mpn_gcd (vp, vp, vsize, up, usize) 131 : mpn_gcd (vp, up, usize, vp, vsize); 132 133 /* Here G <-- V << (g_zero_limbs*GMP_LIMB_BITS + g_zero_bits). */ 134 gsize = vsize + g_zero_limbs; 135 if (g_zero_bits != 0) 136 { 137 mp_limb_t cy_limb; 138 gsize += (vp[vsize - 1] >> (GMP_NUMB_BITS - g_zero_bits)) != 0; 139 MPZ_REALLOC (g, gsize); 140 MPN_ZERO (PTR (g), g_zero_limbs); 141 142 tp = PTR(g) + g_zero_limbs; 143 cy_limb = mpn_lshift (tp, vp, vsize, g_zero_bits); 144 if (cy_limb != 0) 145 tp[vsize] = cy_limb; 146 } 147 else 148 { 149 MPZ_REALLOC (g, gsize); 150 MPN_ZERO (PTR (g), g_zero_limbs); 151 MPN_COPY (PTR (g) + g_zero_limbs, vp, vsize); 152 } 153 154 SIZ (g) = gsize; 155 TMP_FREE; 156 } 157