Line data    Source code

       1             : /* buffer-lcm.c - compute a good buffer size for dealing with two files
       2             : 
       3             :    Copyright (C) 2002, 2005 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 <http://www.gnu.org/licenses/>.  */
      17             : 
      18             : /* Written by Paul Eggert.  */
      19             : 
      20             : #include "buffer-lcm.h"
      21             : 
      22             : /* Return a buffer size suitable for doing I/O with files whose block
      23             :    sizes are A and B.  However, never return a value greater than
      24             :    LCM_MAX.  */
      25             : 
      26             : size_t
      27          33 : buffer_lcm (size_t a, size_t b, size_t lcm_max)
      28             : {
      29             :   size_t size;
      30             : 
      31             :   /* Use reasonable values if buffer sizes are zero.  */
      32          33 :   if (!a)
      33           0 :     size = b ? b : 8 * 1024;
      34             :   else
      35             :     {
      36          33 :       if (b)
      37             :         {
      38             :           /* Return lcm (A, B) if it is in range; otherwise, fall back
      39             :              on A.  */
      40             : 
      41             :           size_t lcm, m, n, q, r;
      42             : 
      43             :           /* N = gcd (A, B).  */
      44          33 :           for (m = a, n = b;  (r = m % n) != 0;  m = n, n = r)
      45           0 :             continue;
      46             : 
      47             :           /* LCM = lcm (A, B), if in range.  */
      48          33 :           q = a / n;
      49          33 :           lcm = q * b;
      50          33 :           if (lcm <= lcm_max && lcm / b == q)
      51          33 :             return lcm;
      52             :         }
      53             : 
      54           0 :       size = a;
      55             :     }
      56             : 
      57           0 :   return size <= lcm_max ? size : lcm_max;
      58             : }