linux/lib/div64.c
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   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
  26uint32_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
  59EXPORT_SYMBOL(__div64_32);
  60
  61/* 64bit divisor, dividend and result. dynamic precision */
  62uint64_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}
  79EXPORT_SYMBOL(div64_64);
  80
  81#endif /* BITS_PER_LONG == 32 */
  82
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