lib/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 #include <linux/module.h>
  21 #include <asm/div64.h>
  22
  23 /* Not needed on 64bit architectures */
  24 #if BITS_PER_LONG == 32
  25
  26 uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
  27 {
  28         uint64_t rem = *n;
  29         uint64_t b = base;
  30         uint64_t res, d = 1;
  31         uint32_t high = rem >> 32;
  32
  33         /* Reduce the thing a bit first */
  34         res = 0;
  35         if (high >= base) {
  36                 high /= base;
  37                 res = (uint64_t) high << 32;
  38                 rem -= (uint64_t) (high*base) << 32;
  39         }
  40
  41         while ((int64_t)b > 0 && b < rem) {
  42                 b = b+b;
  43                 d = d+d;
  44         }
  45
  46         do {
  47                 if (rem >= b) {
  48                         rem -= b;
  49                         res += d;
  50                 }
  51                 b >>= 1;
  52                 d >>= 1;
  53         } while (d);
  54
  55         *n = res;
  56         return rem;
  57 }
  58
  59 EXPORT_SYMBOL(__div64_32);
  60
  61 /* 64bit divisor, dividend and result. dynamic precision */
  62 uint64_t div64_64(uint64_t dividend, uint64_t divisor)
  63 {
  64         uint32_t high, d;
  65
  66         high = divisor >> 32;
  67         if (high) {
  68                 unsigned int shift = fls(high);
  69
  70                 d = divisor >> shift;
  71                 dividend >>= shift;
  72         } else
  73                 d = divisor;
  74
  75         do_div(dividend, d);
  76
  77         return dividend;
  78 }
  79 EXPORT_SYMBOL(div64_64);
  80
  81 #endif /* BITS_PER_LONG == 32 */