1 | /* mpz_addmul_ui, mpz_submul_ui - add or subtract small multiple. |
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2 | |
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3 | THE mpz_aorsmul_1 FUNCTION IN THIS FILE IS FOR INTERNAL USE ONLY AND IS |
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4 | ALMOST CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR |
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5 | COMPLETELY IN FUTURE GNU MP RELEASES. |
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6 | |
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7 | Copyright 2001, 2002, 2004 Free Software Foundation, Inc. |
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8 | |
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9 | This file is part of the GNU MP Library. |
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10 | |
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11 | The GNU MP Library is free software; you can redistribute it and/or modify |
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12 | it under the terms of the GNU Lesser General Public License as published by |
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13 | the Free Software Foundation; either version 2.1 of the License, or (at your |
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14 | option) any later version. |
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15 | |
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16 | The GNU MP Library is distributed in the hope that it will be useful, but |
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17 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
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18 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
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19 | License for more details. |
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20 | |
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21 | You should have received a copy of the GNU Lesser General Public License |
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22 | along with the GNU MP Library; see the file COPYING.LIB. If not, write to |
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23 | the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
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24 | MA 02111-1307, USA. */ |
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25 | |
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26 | #include "gmp.h" |
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27 | #include "gmp-impl.h" |
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28 | |
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29 | |
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30 | #if HAVE_NATIVE_mpn_mul_1c |
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31 | #define MPN_MUL_1C(cout, dst, src, size, n, cin) \ |
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32 | do { \ |
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33 | (cout) = mpn_mul_1c (dst, src, size, n, cin); \ |
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34 | } while (0) |
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35 | #else |
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36 | #define MPN_MUL_1C(cout, dst, src, size, n, cin) \ |
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37 | do { \ |
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38 | mp_limb_t __cy; \ |
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39 | __cy = mpn_mul_1 (dst, src, size, n); \ |
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40 | (cout) = __cy + mpn_add_1 (dst, dst, size, cin); \ |
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41 | } while (0) |
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42 | #endif |
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43 | |
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44 | |
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45 | /* sub>=0 means an addmul w += x*y, sub<0 means a submul w -= x*y. |
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46 | |
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47 | All that's needed to account for negative w or x is to flip "sub". |
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48 | |
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49 | The final w will retain its sign, unless an underflow occurs in a submul |
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50 | of absolute values, in which case it's flipped. |
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51 | |
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52 | If x has more limbs than w, then mpn_submul_1 followed by mpn_com_n is |
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53 | used. The alternative would be mpn_mul_1 into temporary space followed |
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54 | by mpn_sub_n. Avoiding temporary space seem good, and submul+com stands |
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55 | a chance of being faster since it involves only one set of carry |
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56 | propagations, not two. Note that doing an addmul_1 with a |
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57 | twos-complement negative y doesn't work, because it effectively adds an |
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58 | extra x * 2^BITS_PER_MP_LIMB. */ |
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59 | |
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60 | REGPARM_ATTR (1) void |
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61 | mpz_aorsmul_1 (mpz_ptr w, mpz_srcptr x, mp_limb_t y, mp_size_t sub) |
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62 | { |
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63 | mp_size_t xsize, wsize, wsize_signed, new_wsize, min_size, dsize; |
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64 | mp_srcptr xp; |
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65 | mp_ptr wp; |
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66 | mp_limb_t cy; |
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67 | |
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68 | /* w unaffected if x==0 or y==0 */ |
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69 | xsize = SIZ (x); |
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70 | if (xsize == 0 || y == 0) |
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71 | return; |
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72 | |
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73 | sub ^= xsize; |
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74 | xsize = ABS (xsize); |
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75 | |
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76 | wsize_signed = SIZ (w); |
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77 | if (wsize_signed == 0) |
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78 | { |
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79 | /* nothing to add to, just set x*y, "sub" gives the sign */ |
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80 | MPZ_REALLOC (w, xsize+1); |
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81 | wp = PTR (w); |
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82 | cy = mpn_mul_1 (wp, PTR(x), xsize, y); |
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83 | wp[xsize] = cy; |
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84 | xsize += (cy != 0); |
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85 | SIZ (w) = (sub >= 0 ? xsize : -xsize); |
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86 | return; |
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87 | } |
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88 | |
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89 | sub ^= wsize_signed; |
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90 | wsize = ABS (wsize_signed); |
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91 | |
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92 | new_wsize = MAX (wsize, xsize); |
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93 | MPZ_REALLOC (w, new_wsize+1); |
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94 | wp = PTR (w); |
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95 | xp = PTR (x); |
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96 | min_size = MIN (wsize, xsize); |
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97 | |
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98 | if (sub >= 0) |
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99 | { |
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100 | /* addmul of absolute values */ |
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101 | |
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102 | cy = mpn_addmul_1 (wp, xp, min_size, y); |
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103 | wp += min_size; |
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104 | xp += min_size; |
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105 | |
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106 | dsize = xsize - wsize; |
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107 | #if HAVE_NATIVE_mpn_mul_1c |
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108 | if (dsize > 0) |
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109 | cy = mpn_mul_1c (wp, xp, dsize, y, cy); |
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110 | else if (dsize < 0) |
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111 | { |
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112 | dsize = -dsize; |
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113 | cy = mpn_add_1 (wp, wp, dsize, cy); |
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114 | } |
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115 | #else |
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116 | if (dsize != 0) |
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117 | { |
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118 | mp_limb_t cy2; |
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119 | if (dsize > 0) |
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120 | cy2 = mpn_mul_1 (wp, xp, dsize, y); |
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121 | else |
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122 | { |
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123 | dsize = -dsize; |
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124 | cy2 = 0; |
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125 | } |
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126 | cy = cy2 + mpn_add_1 (wp, wp, dsize, cy); |
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127 | } |
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128 | #endif |
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129 | |
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130 | wp[dsize] = cy; |
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131 | new_wsize += (cy != 0); |
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132 | } |
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133 | else |
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134 | { |
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135 | /* submul of absolute values */ |
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136 | |
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137 | cy = mpn_submul_1 (wp, xp, min_size, y); |
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138 | if (wsize >= xsize) |
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139 | { |
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140 | /* if w bigger than x, then propagate borrow through it */ |
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141 | if (wsize != xsize) |
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142 | cy = mpn_sub_1 (wp+xsize, wp+xsize, wsize-xsize, cy); |
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143 | |
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144 | if (cy != 0) |
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145 | { |
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146 | /* Borrow out of w, take twos complement negative to get |
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147 | absolute value, flip sign of w. */ |
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148 | wp[new_wsize] = ~-cy; /* extra limb is 0-cy */ |
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149 | mpn_com_n (wp, wp, new_wsize); |
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150 | new_wsize++; |
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151 | MPN_INCR_U (wp, new_wsize, CNST_LIMB(1)); |
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152 | wsize_signed = -wsize_signed; |
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153 | } |
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154 | } |
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155 | else /* wsize < xsize */ |
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156 | { |
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157 | /* x bigger than w, so want x*y-w. Submul has given w-x*y, so |
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158 | take twos complement and use an mpn_mul_1 for the rest. */ |
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159 | |
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160 | mp_limb_t cy2; |
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161 | |
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162 | /* -(-cy*b^n + w-x*y) = (cy-1)*b^n + ~(w-x*y) + 1 */ |
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163 | mpn_com_n (wp, wp, wsize); |
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164 | cy += mpn_add_1 (wp, wp, wsize, CNST_LIMB(1)); |
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165 | cy -= 1; |
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166 | |
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167 | /* If cy-1 == -1 then hold that -1 for latter. mpn_submul_1 never |
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168 | returns cy==MP_LIMB_T_MAX so that value always indicates a -1. */ |
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169 | cy2 = (cy == MP_LIMB_T_MAX); |
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170 | cy += cy2; |
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171 | MPN_MUL_1C (cy, wp+wsize, xp+wsize, xsize-wsize, y, cy); |
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172 | wp[new_wsize] = cy; |
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173 | new_wsize += (cy != 0); |
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174 | |
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175 | /* Apply any -1 from above. The value at wp+wsize is non-zero |
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176 | because y!=0 and the high limb of x will be non-zero. */ |
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177 | if (cy2) |
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178 | MPN_DECR_U (wp+wsize, new_wsize-wsize, CNST_LIMB(1)); |
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179 | |
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180 | wsize_signed = -wsize_signed; |
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181 | } |
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182 | |
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183 | /* submul can produce high zero limbs due to cancellation, both when w |
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184 | has more limbs or x has more */ |
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185 | MPN_NORMALIZE (wp, new_wsize); |
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186 | } |
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187 | |
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188 | SIZ (w) = (wsize_signed >= 0 ? new_wsize : -new_wsize); |
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189 | |
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190 | ASSERT (new_wsize == 0 || PTR(w)[new_wsize-1] != 0); |
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191 | } |
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192 | |
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193 | |
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194 | void |
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195 | mpz_addmul_ui (mpz_ptr w, mpz_srcptr x, unsigned long y) |
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196 | { |
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197 | mpz_aorsmul_1 (w, x, (mp_limb_t) y & GMP_NUMB_MASK, (mp_size_t) 0); |
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198 | #if GMP_NAIL_BITS != 0 |
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199 | if (y > GMP_NUMB_MAX && SIZ(x) != 0) |
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200 | { |
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201 | mpz_t t; |
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202 | mp_ptr tp; |
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203 | mp_size_t xn; |
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204 | TMP_DECL (mark); |
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205 | TMP_MARK (mark); |
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206 | xn = SIZ (x); |
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207 | MPZ_TMP_INIT (t, ABS (xn) + 1); |
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208 | tp = PTR (t); |
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209 | tp[0] = 0; |
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210 | MPN_COPY (tp + 1, PTR(x), ABS (xn)); |
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211 | SIZ(t) = xn >= 0 ? xn + 1 : xn - 1; |
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212 | mpz_aorsmul_1 (w, t, (mp_limb_t) y >> GMP_NUMB_BITS, (mp_size_t) 0); |
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213 | TMP_FREE (mark); |
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214 | } |
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215 | #endif |
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216 | } |
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217 | |
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218 | void |
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219 | mpz_submul_ui (mpz_ptr w, mpz_srcptr x, unsigned long y) |
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220 | { |
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221 | mpz_aorsmul_1 (w, x, (mp_limb_t) y & GMP_NUMB_MASK, (mp_size_t) -1); |
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222 | #if GMP_NAIL_BITS != 0 |
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223 | if (y > GMP_NUMB_MAX && SIZ(x) != 0) |
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224 | { |
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225 | mpz_t t; |
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226 | mp_ptr tp; |
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227 | mp_size_t xn; |
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228 | TMP_DECL (mark); |
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229 | TMP_MARK (mark); |
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230 | xn = SIZ (x); |
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231 | MPZ_TMP_INIT (t, ABS (xn) + 1); |
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232 | tp = PTR (t); |
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233 | tp[0] = 0; |
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234 | MPN_COPY (tp + 1, PTR(x), ABS (xn)); |
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235 | SIZ(t) = xn >= 0 ? xn + 1 : xn - 1; |
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236 | mpz_aorsmul_1 (w, t, (mp_limb_t) y >> GMP_NUMB_BITS, (mp_size_t) -1); |
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237 | TMP_FREE (mark); |
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238 | } |
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239 | #endif |
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240 | } |
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