LXR linux/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 * or by defining a preprocessor macro in arch/include/asm/div64.h.
  18 */
  19
  20#include <linux/export.h>
  21#include <linux/kernel.h>
  22#include <linux/math64.h>
  23
  24/* Not needed on 64bit architectures */
  25#if BITS_PER_LONG == 32
  26
  27#ifndef __div64_32
  28uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
  29{
  30        uint64_t rem = *n;
  31        uint64_t b = base;
  32        uint64_t res, d = 1;
  33        uint32_t high = rem >> 32;
  34
  35        /* Reduce the thing a bit first */
  36        res = 0;
  37        if (high >= base) {
  38                high /= base;
  39                res = (uint64_t) high << 32;
  40                rem -= (uint64_t) (high*base) << 32;
  41        }
  42
  43        while ((int64_t)b > 0 && b < rem) {
  44                b = b+b;
  45                d = d+d;
  46        }
  47
  48        do {
  49                if (rem >= b) {
  50                        rem -= b;
  51                        res += d;
  52                }
  53                b >>= 1;
  54                d >>= 1;
  55        } while (d);
  56
  57        *n = res;
  58        return rem;
  59}
  60EXPORT_SYMBOL(__div64_32);
  61#endif
  62
  63#ifndef div_s64_rem
  64s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
  65{
  66        u64 quotient;
  67
  68        if (dividend < 0) {
  69                quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
  70                *remainder = -*remainder;
  71                if (divisor > 0)
  72                        quotient = -quotient;
  73        } else {
  74                quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
  75                if (divisor < 0)
  76                        quotient = -quotient;
  77        }
  78        return quotient;
  79}
  80EXPORT_SYMBOL(div_s64_rem);
  81#endif
  82
  83/**
  84 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
  85 * @dividend:   64bit dividend
  86 * @divisor:    64bit divisor
  87 * @remainder:  64bit remainder
  88 *
  89 * This implementation is a comparable to algorithm used by div64_u64.
  90 * But this operation, which includes math for calculating the remainder,
  91 * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
  92 * systems.
  93 */
  94#ifndef div64_u64_rem
  95u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
  96{
  97        u32 high = divisor >> 32;
  98        u64 quot;
  99
 100        if (high == 0) {
 101                u32 rem32;
 102                quot = div_u64_rem(dividend, divisor, &rem32);
 103                *remainder = rem32;
 104        } else {
 105                int n = 1 + fls(high);
 106                quot = div_u64(dividend >> n, divisor >> n);
 107
 108                if (quot != 0)
 109                        quot--;
 110
 111                *remainder = dividend - quot * divisor;
 112                if (*remainder >= divisor) {
 113                        quot++;
 114                        *remainder -= divisor;
 115                }
 116        }
 117
 118        return quot;
 119}
 120EXPORT_SYMBOL(div64_u64_rem);
 121#endif
 122
 123/**
 124 * div64_u64 - unsigned 64bit divide with 64bit divisor
 125 * @dividend:   64bit dividend
 126 * @divisor:    64bit divisor
 127 *
 128 * This implementation is a modified version of the algorithm proposed
 129 * by the book 'Hacker's Delight'.  The original source and full proof
 130 * can be found here and is available for use without restriction.
 131 *
 132 * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
 133 */
 134#ifndef div64_u64
 135u64 div64_u64(u64 dividend, u64 divisor)
 136{
 137        u32 high = divisor >> 32;
 138        u64 quot;
 139
 140        if (high == 0) {
 141                quot = div_u64(dividend, divisor);
 142        } else {
 143                int n = 1 + fls(high);
 144                quot = div_u64(dividend >> n, divisor >> n);
 145
 146                if (quot != 0)
 147                        quot--;
 148                if ((dividend - quot * divisor) >= divisor)
 149                        quot++;
 150        }
 151
 152        return quot;
 153}
 154EXPORT_SYMBOL(div64_u64);
 155#endif
 156
 157/**
 158 * div64_s64 - signed 64bit divide with 64bit divisor
 159 * @dividend:   64bit dividend
 160 * @divisor:    64bit divisor
 161 */
 162#ifndef div64_s64
 163s64 div64_s64(s64 dividend, s64 divisor)
 164{
 165        s64 quot, t;
 166
 167        quot = div64_u64(abs(dividend), abs(divisor));
 168        t = (dividend ^ divisor) >> 63;
 169
 170        return (quot ^ t) - t;
 171}
 172EXPORT_SYMBOL(div64_s64);
 173#endif
 174
 175#endif /* BITS_PER_LONG == 32 */
 176
 177/*
 178 * Iterative div/mod for use when dividend is not expected to be much
 179 * bigger than divisor.
 180 */
 181u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
 182{
 183        return __iter_div_u64_rem(dividend, divisor, remainder);
 184}
 185EXPORT_SYMBOL(iter_div_u64_rem);
 186