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
  28 uint32_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 }
  60 EXPORT_SYMBOL(__div64_32);
  61 #endif
  62
  63 #ifndef div_s64_rem
  64 s64 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 }
  80 EXPORT_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
  95 u64 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 = 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 }
 120 EXPORT_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
 135 u64 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 = 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 }
 154 EXPORT_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
 163 s64 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 }
 172 EXPORT_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  */
 181 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
 182 {
 183         return __iter_div_u64_rem(dividend, divisor, remainder);
 184 }
 185 EXPORT_SYMBOL(iter_div_u64_rem);