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6b628d36 | 1 | /* mpn_submul_1 -- multiply the S1_SIZE long limb vector pointed to by S1_PTR |
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2 | by S2_LIMB, subtract the S1_SIZE least significant limbs of the product |
3 | from the limb vector pointed to by RES_PTR. Return the most significant | |
4 | limb of the product, adjusted for carry-out from the subtraction. | |
5 | ||
a334319f | 6 | Copyright (C) 1992, 1993, 1994, 1996 Free Software Foundation, Inc. |
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7 | |
8 | This file is part of the GNU MP Library. | |
9 | ||
10 | The GNU MP Library is free software; you can redistribute it and/or modify | |
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11 | it under the terms of the GNU Lesser General Public License as published by |
12 | the Free Software Foundation; either version 2.1 of the License, or (at your | |
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13 | option) any later version. |
14 | ||
15 | The GNU MP Library is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY | |
6d84f89a | 17 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
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18 | License for more details. |
19 | ||
6d84f89a | 20 | You should have received a copy of the GNU Lesser General Public License |
28f540f4 | 21 | along with the GNU MP Library; see the file COPYING.LIB. If not, write to |
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22 | the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
23 | MA 02111-1307, USA. */ | |
28f540f4 | 24 | |
a334319f | 25 | #include "gmp.h" |
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26 | #include "gmp-impl.h" |
27 | #include "longlong.h" | |
28 | ||
b928942e | 29 | mp_limb_t |
6b628d36 | 30 | mpn_submul_1 (res_ptr, s1_ptr, s1_size, s2_limb) |
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31 | register mp_ptr res_ptr; |
32 | register mp_srcptr s1_ptr; | |
33 | mp_size_t s1_size; | |
b928942e | 34 | register mp_limb_t s2_limb; |
28f540f4 | 35 | { |
b928942e | 36 | register mp_limb_t cy_limb; |
28f540f4 | 37 | register mp_size_t j; |
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38 | register mp_limb_t prod_high, prod_low; |
39 | register mp_limb_t x; | |
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40 | |
41 | /* The loop counter and index J goes from -SIZE to -1. This way | |
42 | the loop becomes faster. */ | |
43 | j = -s1_size; | |
44 | ||
45 | /* Offset the base pointers to compensate for the negative indices. */ | |
46 | res_ptr -= j; | |
47 | s1_ptr -= j; | |
48 | ||
49 | cy_limb = 0; | |
50 | do | |
51 | { | |
52 | umul_ppmm (prod_high, prod_low, s1_ptr[j], s2_limb); | |
53 | ||
54 | prod_low += cy_limb; | |
55 | cy_limb = (prod_low < cy_limb) + prod_high; | |
56 | ||
57 | x = res_ptr[j]; | |
58 | prod_low = x - prod_low; | |
59 | cy_limb += (prod_low > x); | |
60 | res_ptr[j] = prod_low; | |
61 | } | |
62 | while (++j != 0); | |
63 | ||
64 | return cy_limb; | |
65 | } |