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/module.h>
  20 #include <linux/math64.h>
  21
  22 /* Not needed on 64bit architectures */
  23 #if BITS_PER_LONG == 32
  24
  25 uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
  26 {
  27         uint64_t rem = *n;
  28         uint64_t b = base;
  29         uint64_t res, d = 1;
  30         uint32_t high = rem >> 32;
  31
  32         /* Reduce the thing a bit first */
  33         res = 0;
  34         if (high >= base) {
  35                 high /= base;
  36                 res = (uint64_t) high << 32;
  37                 rem -= (uint64_t) (high*base) << 32;
  38         }
  39
  40         while ((int64_t)b > 0 && b < rem) {
  41                 b = b+b;
  42                 d = d+d;
  43         }
  44
  45         do {
  46                 if (rem >= b) {
  47                         rem -= b;
  48                         res += d;
  49                 }
  50                 b >>= 1;
  51                 d >>= 1;
  52         } while (d);
  53
  54         *n = res;
  55         return rem;
  56 }
  57
  58 EXPORT_SYMBOL(__div64_32);
  59
  60 #ifndef div_s64_rem
  61 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
  62 {
  63         u64 quotient;
  64
  65         if (dividend < 0) {
  66                 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
  67                 *remainder = -*remainder;
  68                 if (divisor > 0)
  69                         quotient = -quotient;
  70         } else {
  71                 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
  72                 if (divisor < 0)
  73                         quotient = -quotient;
  74         }
  75         return quotient;
  76 }
  77 EXPORT_SYMBOL(div_s64_rem);
  78 #endif
  79
  80 /**
  81  * div64_u64 - unsigned 64bit divide with 64bit divisor
  82  * @dividend:   64bit dividend
  83  * @divisor:    64bit divisor
  84  *
  85  * This implementation is a modified version of the algorithm proposed
  86  * by the book 'Hacker's Delight'.  The original source and full proof
  87  * can be found here and is available for use without restriction.
  88  *
  89  * 'http://www.hackersdelight.org/HDcode/newCode/divDouble.c'
  90  */
  91 #ifndef div64_u64
  92 u64 div64_u64(u64 dividend, u64 divisor)
  93 {
  94         u32 high = divisor >> 32;
  95         u64 quot;
  96
  97         if (high == 0) {
  98                 quot = div_u64(dividend, divisor);
  99         } else {
 100                 int n = 1 + fls(high);
 101                 quot = div_u64(dividend >> n, divisor >> n);
 102
 103                 if (quot != 0)
 104                         quot--;
 105                 if ((dividend - quot * divisor) >= divisor)
 106                         quot++;
 107         }
 108
 109         return quot;
 110 }
 111 EXPORT_SYMBOL(div64_u64);
 112 #endif
 113
 114 /**
 115  * div64_s64 - signed 64bit divide with 64bit divisor
 116  * @dividend:   64bit dividend
 117  * @divisor:    64bit divisor
 118  */
 119 #ifndef div64_s64
 120 s64 div64_s64(s64 dividend, s64 divisor)
 121 {
 122         s64 quot, t;
 123
 124         quot = div64_u64(abs64(dividend), abs64(divisor));
 125         t = (dividend ^ divisor) >> 63;
 126
 127         return (quot ^ t) - t;
 128 }
 129 EXPORT_SYMBOL(div64_s64);
 130 #endif
 131
 132 #endif /* BITS_PER_LONG == 32 */
 133
 134 /*
 135  * Iterative div/mod for use when dividend is not expected to be much
 136  * bigger than divisor.
 137  */
 138 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
 139 {
 140         return __iter_div_u64_rem(dividend, divisor, remainder);
 141 }
 142 EXPORT_SYMBOL(iter_div_u64_rem);