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/export.h>
  20 #include <linux/kernel.h>
  21 #include <linux/math64.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 #ifndef div_s64_rem
  62 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
  63 {
  64         u64 quotient;
  65
  66         if (dividend < 0) {
  67                 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
  68                 *remainder = -*remainder;
  69                 if (divisor > 0)
  70                         quotient = -quotient;
  71         } else {
  72                 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
  73                 if (divisor < 0)
  74                         quotient = -quotient;
  75         }
  76         return quotient;
  77 }
  78 EXPORT_SYMBOL(div_s64_rem);
  79 #endif
  80
  81 /**
  82  * div64_u64_rem - unsigned 64bit divide with 64bit divisor and 64bit remainder
  83  * @dividend:   64bit dividend
  84  * @divisor:    64bit divisor
  85  * @remainder:  64bit remainder
  86  *
  87  * This implementation is a modified version of the algorithm proposed
  88  * by the book 'Hacker's Delight'.  The original source and full proof
  89  * can be found here and is available for use without restriction.
  90  *
  91  * 'http://www.hackersdelight.org/HDcode/newCode/divDouble.c.txt'
  92  */
  93 #ifndef div64_u64_rem
  94 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
  95 {
  96         u32 high = divisor >> 32;
  97         u64 quot;
  98
  99         if (high == 0) {
 100                 u32 rem32;
 101                 quot = div_u64_rem(dividend, divisor, &rem32);
 102                 *remainder = rem32;
 103         } else {
 104                 int n = 1 + fls(high);
 105                 quot = div_u64(dividend >> n, divisor >> n);
 106
 107                 if (quot != 0)
 108                         quot--;
 109
 110                 *remainder = dividend - quot * divisor;
 111                 if (*remainder >= divisor) {
 112                         quot++;
 113                         *remainder -= divisor;
 114                 }
 115         }
 116
 117         return quot;
 118 }
 119 EXPORT_SYMBOL(div64_u64_rem);
 120 #endif
 121
 122 /**
 123  * div64_s64 - signed 64bit divide with 64bit divisor
 124  * @dividend:   64bit dividend
 125  * @divisor:    64bit divisor
 126  */
 127 #ifndef div64_s64
 128 s64 div64_s64(s64 dividend, s64 divisor)
 129 {
 130         s64 quot, t;
 131
 132         quot = div64_u64(abs64(dividend), abs64(divisor));
 133         t = (dividend ^ divisor) >> 63;
 134
 135         return (quot ^ t) - t;
 136 }
 137 EXPORT_SYMBOL(div64_s64);
 138 #endif
 139
 140 #endif /* BITS_PER_LONG == 32 */
 141
 142 /*
 143  * Iterative div/mod for use when dividend is not expected to be much
 144  * bigger than divisor.
 145  */
 146 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
 147 {
 148         return __iter_div_u64_rem(dividend, divisor, remainder);
 149 }
 150 EXPORT_SYMBOL(iter_div_u64_rem);