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 2, or (at your option)
    8:    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, write to the Free Software Foundation,
   17:    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
   18: 
   19: /* Written by Paul Eggert.  */
   20: 
   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
   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: }