lib_generic/div64.c

   1 /*
   2  * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
   3  *
   4  * Based on former do_div() implementation from asm-parisc/div64.h:
   5  *      Copyright (C) 1999 Hewlett-Packard Co
   6  *      Copyright (C) 1999 David Mosberger-Tang <davidm@hpl.hp.com>
   7  *
   8  *
   9  * Generic C version of 64bit/32bit division and modulo, with
  10  * 64bit result and 32bit remainder.
  11  *
  12  * The fast case for (n>>32 == 0) is handled inline by do_div().
  13  *
  14  * Code generated for this function might be very inefficient
  15  * for some CPUs. __div64_32() can be overridden by linking arch-specific
  16  * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S.
  17  */
  18
  19 #include <linux/types.h>
  20
  21 uint32_t __div64_32(uint64_t *n, uint32_t base)
  22 {
  23         uint64_t rem = *n;
  24         uint64_t b = base;
  25         uint64_t res, d = 1;
  26         uint32_t high = rem >> 32;
  27
  28         /* Reduce the thing a bit first */
  29         res = 0;
  30         if (high >= base) {
  31                 high /= base;
  32                 res = (uint64_t) high << 32;
  33                 rem -= (uint64_t) (high*base) << 32;
  34         }
  35
  36         while ((int64_t)b > 0 && b < rem) {
  37                 b = b+b;
  38                 d = d+d;
  39         }
  40
  41         do {
  42                 if (rem >= b) {
  43                         rem -= b;
  44                         res += d;
  45                 }
  46                 b >>= 1;
  47                 d >>= 1;
  48         } while (d);
  49
  50         *n = res;
  51         return rem;
  52 }