1 /* mpn_sub -- Subtract two low-level natural-number integers.
3 Copyright (C) 1991 Free Software Foundation, Inc.
5 This file is part of the GNU MP Library.
7 The GNU MP Library is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 2, or (at your option)
12 The GNU MP Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with the GNU MP Library; see the file COPYING. If not, write to
19 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
24 /* Subtract SUB_PTR/SUB_SIZE from MIN_PTR/MIN_SIZE and store the
25 result (MIN_SIZE words) at DIF_PTR.
27 Return 1 if min < sub (result is negative). Otherwise, return the
28 negative difference between the number of words in dif and min.
29 (I.e. return 0 if the result has MIN_SIZE words, -1 if it has
30 MIN_SIZE - 1 words, etc.)
32 Argument constraint: MIN_SIZE >= SUB_SIZE.
34 The size of DIF can be calculated as MIN_SIZE + the return value. */
38 mpn_sub (mp_ptr dif_ptr,
39 mp_srcptr min_ptr, mp_size min_size,
40 mp_srcptr sub_ptr, mp_size sub_size)
42 mpn_sub (dif_ptr, min_ptr, min_size, sub_ptr, sub_size)
53 /* The loop counter and index J goes from some negative value to zero.
54 This way the loops are faster. Need to offset the base pointers
55 to take care of the negative indices. */
65 /* There are two do-loops, marked NON-CARRY LOOP and CARRY LOOP that
66 jump between each other. The first loop is for when the previous
67 subtraction didn't produce a carry-out; the second is for the
68 complementary case. */
84 /* We have exhausted SUB, with no carry out. Copy remaining part of
88 j = sub_size - min_size;
90 /* If there's no difference between the length of the operands, the
91 last words might have become zero, and re-normalization is needed. */
114 /* We have exhausted SUB, but need to propagate carry. */
116 j = sub_size - min_size;
118 return 1; /* min < sub. Flag it to the caller */
123 /* Propagate carry. Sooner or later the carry will cancel with a
124 non-zero word, because the minuend is normalized. Considering this,
125 there's no need to test the index J. */
140 /* Don't copy the remaining words of MIN to DIF if MIN_PTR and DIF_PTR
141 are equal. It would just be a no-op copying. Return 0, as the length
142 of the result equals that of the minuend. */
143 if (dif_ptr == min_ptr)
148 dif_ptr[j] = min_ptr[j];
155 for (j = -1; j >= -min_size; j--)