1 /* buffer-lcm.c - compute a good buffer size for dealing with two files
2
3 Copyright (C) 2002-2023 Free Software Foundation, Inc.
4
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 /* Written by Paul Eggert. */
19
20 #include <config.h>
21 #include "buffer-lcm.h"
22
23 /* Return a buffer size suitable for doing I/O with files whose block
24 sizes are A and B. However, never return a value greater than
25 LCM_MAX. */
26
27 size_t
buffer_lcm(size_t a,size_t b,size_t lcm_max)28 buffer_lcm (size_t a, size_t b, size_t lcm_max)
29 {
30 size_t size;
31
32 /* Use reasonable values if buffer sizes are zero. */
33 if (!a)
34 size = b ? b : 8 * 1024;
35 else
36 {
37 if (b)
38 {
39 /* Return lcm (A, B) if it is in range; otherwise, fall back
40 on A. */
41
42 size_t lcm, m, n, q, r;
43
44 /* N = gcd (A, B). */
45 for (m = a, n = b; (r = m % n) != 0; m = n, n = r)
46 continue;
47
48 /* LCM = lcm (A, B), if in range. */
49 q = a / n;
50 lcm = q * b;
51 if (lcm <= lcm_max && lcm / b == q)
52 return lcm;
53 }
54
55 size = a;
56 }
57
58 return size <= lcm_max ? size : lcm_max;
59 }
60