1 /* mpz_addmul_ui, mpz_submul_ui - add or subtract small multiple. 2 3 THE mpz_aorsmul_1 FUNCTION IN THIS FILE IS FOR INTERNAL USE ONLY AND IS 4 ALMOST CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR 5 COMPLETELY IN FUTURE GNU MP RELEASES. 6 7 Copyright 2001, 2002, 2004, 2005 Free Software Foundation, Inc. 8 9 This file is part of the GNU MP Library. 10 11 The GNU MP Library is free software; you can redistribute it and/or modify 12 it under the terms of the GNU Lesser General Public License as published by 13 the Free Software Foundation; either version 3 of the License, or (at your 14 option) any later version. 15 16 The GNU MP Library is distributed in the hope that it will be useful, but 17 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 18 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 19 License for more details. 20 21 You should have received a copy of the GNU Lesser General Public License 22 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 23 24 #include "gmp.h" 25 #include "gmp-impl.h" 26 27 28 #if HAVE_NATIVE_mpn_mul_1c 29 #define MPN_MUL_1C(cout, dst, src, size, n, cin) \ 30 do { \ 31 (cout) = mpn_mul_1c (dst, src, size, n, cin); \ 32 } while (0) 33 #else 34 #define MPN_MUL_1C(cout, dst, src, size, n, cin) \ 35 do { \ 36 mp_limb_t __cy; \ 37 __cy = mpn_mul_1 (dst, src, size, n); \ 38 (cout) = __cy + mpn_add_1 (dst, dst, size, cin); \ 39 } while (0) 40 #endif 41 42 43 /* sub>=0 means an addmul w += x*y, sub<0 means a submul w -= x*y. 44 45 All that's needed to account for negative w or x is to flip "sub". 46 47 The final w will retain its sign, unless an underflow occurs in a submul 48 of absolute values, in which case it's flipped. 49 50 If x has more limbs than w, then mpn_submul_1 followed by mpn_com is 51 used. The alternative would be mpn_mul_1 into temporary space followed 52 by mpn_sub_n. Avoiding temporary space seem good, and submul+com stands 53 a chance of being faster since it involves only one set of carry 54 propagations, not two. Note that doing an addmul_1 with a 55 twos-complement negative y doesn't work, because it effectively adds an 56 extra x * 2^GMP_LIMB_BITS. */ 57 58 REGPARM_ATTR(1) void 59 mpz_aorsmul_1 (mpz_ptr w, mpz_srcptr x, mp_limb_t y, mp_size_t sub) 60 { 61 mp_size_t xsize, wsize, wsize_signed, new_wsize, min_size, dsize; 62 mp_srcptr xp; 63 mp_ptr wp; 64 mp_limb_t cy; 65 66 /* w unaffected if x==0 or y==0 */ 67 xsize = SIZ (x); 68 if (xsize == 0 || y == 0) 69 return; 70 71 sub ^= xsize; 72 xsize = ABS (xsize); 73 74 wsize_signed = SIZ (w); 75 if (wsize_signed == 0) 76 { 77 /* nothing to add to, just set x*y, "sub" gives the sign */ 78 MPZ_REALLOC (w, xsize+1); 79 wp = PTR (w); 80 cy = mpn_mul_1 (wp, PTR(x), xsize, y); 81 wp[xsize] = cy; 82 xsize += (cy != 0); 83 SIZ (w) = (sub >= 0 ? xsize : -xsize); 84 return; 85 } 86 87 sub ^= wsize_signed; 88 wsize = ABS (wsize_signed); 89 90 new_wsize = MAX (wsize, xsize); 91 MPZ_REALLOC (w, new_wsize+1); 92 wp = PTR (w); 93 xp = PTR (x); 94 min_size = MIN (wsize, xsize); 95 96 if (sub >= 0) 97 { 98 /* addmul of absolute values */ 99 100 cy = mpn_addmul_1 (wp, xp, min_size, y); 101 wp += min_size; 102 xp += min_size; 103 104 dsize = xsize - wsize; 105 #if HAVE_NATIVE_mpn_mul_1c 106 if (dsize > 0) 107 cy = mpn_mul_1c (wp, xp, dsize, y, cy); 108 else if (dsize < 0) 109 { 110 dsize = -dsize; 111 cy = mpn_add_1 (wp, wp, dsize, cy); 112 } 113 #else 114 if (dsize != 0) 115 { 116 mp_limb_t cy2; 117 if (dsize > 0) 118 cy2 = mpn_mul_1 (wp, xp, dsize, y); 119 else 120 { 121 dsize = -dsize; 122 cy2 = 0; 123 } 124 cy = cy2 + mpn_add_1 (wp, wp, dsize, cy); 125 } 126 #endif 127 128 wp[dsize] = cy; 129 new_wsize += (cy != 0); 130 } 131 else 132 { 133 /* submul of absolute values */ 134 135 cy = mpn_submul_1 (wp, xp, min_size, y); 136 if (wsize >= xsize) 137 { 138 /* if w bigger than x, then propagate borrow through it */ 139 if (wsize != xsize) 140 cy = mpn_sub_1 (wp+xsize, wp+xsize, wsize-xsize, cy); 141 142 if (cy != 0) 143 { 144 /* Borrow out of w, take twos complement negative to get 145 absolute value, flip sign of w. */ 146 wp[new_wsize] = ~-cy; /* extra limb is 0-cy */ 147 mpn_com (wp, wp, new_wsize); 148 new_wsize++; 149 MPN_INCR_U (wp, new_wsize, CNST_LIMB(1)); 150 wsize_signed = -wsize_signed; 151 } 152 } 153 else /* wsize < xsize */ 154 { 155 /* x bigger than w, so want x*y-w. Submul has given w-x*y, so 156 take twos complement and use an mpn_mul_1 for the rest. */ 157 158 mp_limb_t cy2; 159 160 /* -(-cy*b^n + w-x*y) = (cy-1)*b^n + ~(w-x*y) + 1 */ 161 mpn_com (wp, wp, wsize); 162 cy += mpn_add_1 (wp, wp, wsize, CNST_LIMB(1)); 163 cy -= 1; 164 165 /* If cy-1 == -1 then hold that -1 for latter. mpn_submul_1 never 166 returns cy==MP_LIMB_T_MAX so that value always indicates a -1. */ 167 cy2 = (cy == MP_LIMB_T_MAX); 168 cy += cy2; 169 MPN_MUL_1C (cy, wp+wsize, xp+wsize, xsize-wsize, y, cy); 170 wp[new_wsize] = cy; 171 new_wsize += (cy != 0); 172 173 /* Apply any -1 from above. The value at wp+wsize is non-zero 174 because y!=0 and the high limb of x will be non-zero. */ 175 if (cy2) 176 MPN_DECR_U (wp+wsize, new_wsize-wsize, CNST_LIMB(1)); 177 178 wsize_signed = -wsize_signed; 179 } 180 181 /* submul can produce high zero limbs due to cancellation, both when w 182 has more limbs or x has more */ 183 MPN_NORMALIZE (wp, new_wsize); 184 } 185 186 SIZ (w) = (wsize_signed >= 0 ? new_wsize : -new_wsize); 187 188 ASSERT (new_wsize == 0 || PTR(w)[new_wsize-1] != 0); 189 } 190 191 192 void 193 mpz_addmul_ui (mpz_ptr w, mpz_srcptr x, unsigned long y) 194 { 195 #if BITS_PER_ULONG > GMP_NUMB_BITS 196 if (UNLIKELY (y > GMP_NUMB_MAX && SIZ(x) != 0)) 197 { 198 mpz_t t; 199 mp_ptr tp; 200 mp_size_t xn; 201 TMP_DECL; 202 TMP_MARK; 203 xn = SIZ (x); 204 MPZ_TMP_INIT (t, ABS (xn) + 1); 205 tp = PTR (t); 206 tp[0] = 0; 207 MPN_COPY (tp + 1, PTR(x), ABS (xn)); 208 SIZ(t) = xn >= 0 ? xn + 1 : xn - 1; 209 mpz_aorsmul_1 (w, t, (mp_limb_t) y >> GMP_NUMB_BITS, (mp_size_t) 0); 210 PTR(t) = tp + 1; 211 SIZ(t) = xn; 212 mpz_aorsmul_1 (w, t, (mp_limb_t) y & GMP_NUMB_MASK, (mp_size_t) 0); 213 TMP_FREE; 214 return; 215 } 216 #endif 217 mpz_aorsmul_1 (w, x, (mp_limb_t) y, (mp_size_t) 0); 218 } 219 220 void 221 mpz_submul_ui (mpz_ptr w, mpz_srcptr x, unsigned long y) 222 { 223 #if BITS_PER_ULONG > GMP_NUMB_BITS 224 if (y > GMP_NUMB_MAX && SIZ(x) != 0) 225 { 226 mpz_t t; 227 mp_ptr tp; 228 mp_size_t xn; 229 TMP_DECL; 230 TMP_MARK; 231 xn = SIZ (x); 232 MPZ_TMP_INIT (t, ABS (xn) + 1); 233 tp = PTR (t); 234 tp[0] = 0; 235 MPN_COPY (tp + 1, PTR(x), ABS (xn)); 236 SIZ(t) = xn >= 0 ? xn + 1 : xn - 1; 237 mpz_aorsmul_1 (w, t, (mp_limb_t) y >> GMP_NUMB_BITS, (mp_size_t) -1); 238 PTR(t) = tp + 1; 239 SIZ(t) = xn; 240 mpz_aorsmul_1 (w, t, (mp_limb_t) y & GMP_NUMB_MASK, (mp_size_t) -1); 241 TMP_FREE; 242 return; 243 } 244 #endif 245 mpz_aorsmul_1 (w, x, (mp_limb_t) y & GMP_NUMB_MASK, (mp_size_t) -1); 246 } 247