lib/e2p/percent.c

   1 /*
   2  * percent.c            - Take percentage of a number
   3  *
   4  * Copyright (C) 2006  Theodore Ts'o <tytso@mit.edu>
   5  *
   6  * %Begin-Header%
   7  * This file may be redistributed under the terms of the GNU Library
   8  * General Public License, version 2.
   9  * %End-Header%
  10  */
  11
  12 #include "e2p.h"
  13
  14 #include <stdlib.h>
  15
  16 /*
  17  * We work really hard to calculate this accurately, while avoiding
  18  * an overflow.  "Is there a hyphen in anal-retentive?"  :-)
  19  */
  20 unsigned int e2p_percent(int percent, unsigned int base)
  21 {
  22         unsigned int mask = ~((1 << (sizeof(unsigned int) - 1) * 8) - 1);
  23
  24         if (!percent)
  25                 return 0;
  26         if (100 % percent == 0)
  27                 return base / (100 / percent);
  28         if (mask & base)
  29                 return (base / 100) * percent;
  30         return base * percent / 100;
  31 }
  32
  33 #ifdef DEBUG
  34 #include <unistd.h>
  35 #include <stdio.h>
  36
  37 main(int argc, char **argv)
  38 {
  39         unsigned int base;
  40         int percent;
  41         char *p;
  42         int log_block_size = 0;
  43
  44         if (argc != 3) {
  45                 fprintf(stderr, "Usage: %s percent base\n", argv[0]);
  46                 exit(1);
  47         }
  48
  49         percent = strtoul(argv[1], &p, 0);
  50         if (p[0] && p[1]) {
  51                 fprintf(stderr, "Bad percent: %s\n", argv[1]);
  52                 exit(1);
  53         }
  54
  55         base = strtoul(argv[2], &p, 0);
  56         if (p[0] && p[1]) {
  57                 fprintf(stderr, "Bad base: %s\n", argv[2]);
  58                 exit(1);
  59         }
  60
  61         printf("%d percent of %u is %u.\n", percent, base,
  62                e2p_percent(percent, base));
  63
  64         exit(0);
  65 }
  66 #endif