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 remainder
  83  * @dividend:   64bit dividend
  84  * @divisor:    64bit divisor
  85  * @remainder:  64bit remainder
  86  *
  87  * This implementation is a comparable to algorithm used by div64_u64.
  88  * But this operation, which includes math for calculating the remainder,
  89  * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
  90  * systems.
  91  */
  92 #ifndef div64_u64_rem
  93 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
  94 {
  95         u32 high = divisor >> 32;
  96         u64 quot;
  97
  98         if (high == 0) {
  99                 u32 rem32;
 100                 quot = div_u64_rem(dividend, divisor, &rem32);
 101                 *remainder = rem32;
 102         } else {
 103                 int n = fls(high);
 104                 quot = div_u64(dividend >> n, divisor >> n);
 105
 106                 if (quot != 0)
 107                         quot--;
 108
 109                 *remainder = dividend - quot * divisor;
 110                 if (*remainder >= divisor) {
 111                         quot++;
 112                         *remainder -= divisor;
 113                 }
 114         }
 115
 116         return quot;
 117 }
 118 EXPORT_SYMBOL(div64_u64_rem);
 119 #endif
 120
 121 /**
 122  * div64_u64 - unsigned 64bit divide with 64bit divisor
 123  * @dividend:   64bit dividend
 124  * @divisor:    64bit divisor
 125  *
 126  * This implementation is a modified version of the algorithm proposed
 127  * by the book 'Hacker's Delight'.  The original source and full proof
 128  * can be found here and is available for use without restriction.
 129  *
 130  * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
 131  */
 132 #ifndef div64_u64
 133 u64 div64_u64(u64 dividend, u64 divisor)
 134 {
 135         u32 high = divisor >> 32;
 136         u64 quot;
 137
 138         if (high == 0) {
 139                 quot = div_u64(dividend, divisor);
 140         } else {
 141                 int n = fls(high);
 142                 quot = div_u64(dividend >> n, divisor >> n);
 143
 144                 if (quot != 0)
 145                         quot--;
 146                 if ((dividend - quot * divisor) >= divisor)
 147                         quot++;
 148         }
 149
 150         return quot;
 151 }
 152 EXPORT_SYMBOL(div64_u64);
 153 #endif
 154
 155 /**
 156  * div64_s64 - signed 64bit divide with 64bit divisor
 157  * @dividend:   64bit dividend
 158  * @divisor:    64bit divisor
 159  */
 160 #ifndef div64_s64
 161 s64 div64_s64(s64 dividend, s64 divisor)
 162 {
 163         s64 quot, t;
 164
 165         quot = div64_u64(abs(dividend), abs(divisor));
 166         t = (dividend ^ divisor) >> 63;
 167
 168         return (quot ^ t) - t;
 169 }
 170 EXPORT_SYMBOL(div64_s64);
 171 #endif
 172
 173 #endif /* BITS_PER_LONG == 32 */
 174
 175 /*
 176  * Iterative div/mod for use when dividend is not expected to be much
 177  * bigger than divisor.
 178  */
 179 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
 180 {
 181         return __iter_div_u64_rem(dividend, divisor, remainder);
 182 }
 183 EXPORT_SYMBOL(iter_div_u64_rem);