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/compat.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 /*
  29  * Don't instrument this function as it may be called from tracing code, since
  30  * it needs to read the timer and this often requires calling do_div(), which
  31  * calls this function.
  32  */
  33 uint32_t __attribute__((weak, no_instrument_function)) __div64_32(u64 *n,
  34                                                                   u32 base)
  35 {
  36         u64 rem = *n;
  37         u64 b = base;
  38         u64 res, d = 1;
  39         u32 high = rem >> 32;
  40
  41         /* Reduce the thing a bit first */
  42         res = 0;
  43         if (high >= base) {
  44                 high /= base;
  45                 res = (u64)high << 32;
  46                 rem -= (u64)(high * base) << 32;
  47         }
  48
  49         while ((int64_t)b > 0 && b < rem) {
  50                 b = b+b;
  51                 d = d+d;
  52         }
  53
  54         do {
  55                 if (rem >= b) {
  56                         rem -= b;
  57                         res += d;
  58                 }
  59                 b >>= 1;
  60                 d >>= 1;
  61         } while (d);
  62
  63         *n = res;
  64         return rem;
  65 }
  66 EXPORT_SYMBOL(__div64_32);
  67 #endif
  68
  69 #ifndef div_s64_rem
  70 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
  71 {
  72         u64 quotient;
  73
  74         if (dividend < 0) {
  75                 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
  76                 *remainder = -*remainder;
  77                 if (divisor > 0)
  78                         quotient = -quotient;
  79         } else {
  80                 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
  81                 if (divisor < 0)
  82                         quotient = -quotient;
  83         }
  84         return quotient;
  85 }
  86 EXPORT_SYMBOL(div_s64_rem);
  87 #endif
  88
  89 /**
  90  * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
  91  * @dividend:   64bit dividend
  92  * @divisor:    64bit divisor
  93  * @remainder:  64bit remainder
  94  *
  95  * This implementation is a comparable to algorithm used by div64_u64.
  96  * But this operation, which includes math for calculating the remainder,
  97  * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
  98  * systems.
  99  */
 100 #ifndef div64_u64_rem
 101 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
 102 {
 103         u32 high = divisor >> 32;
 104         u64 quot;
 105
 106         if (high == 0) {
 107                 u32 rem32;
 108                 quot = div_u64_rem(dividend, divisor, &rem32);
 109                 *remainder = rem32;
 110         } else {
 111                 int n = 1 + fls(high);
 112                 quot = div_u64(dividend >> n, divisor >> n);
 113
 114                 if (quot != 0)
 115                         quot--;
 116
 117                 *remainder = dividend - quot * divisor;
 118                 if (*remainder >= divisor) {
 119                         quot++;
 120                         *remainder -= divisor;
 121                 }
 122         }
 123
 124         return quot;
 125 }
 126 EXPORT_SYMBOL(div64_u64_rem);
 127 #endif
 128
 129 /**
 130  * div64_u64 - unsigned 64bit divide with 64bit divisor
 131  * @dividend:   64bit dividend
 132  * @divisor:    64bit divisor
 133  *
 134  * This implementation is a modified version of the algorithm proposed
 135  * by the book 'Hacker's Delight'.  The original source and full proof
 136  * can be found here and is available for use without restriction.
 137  *
 138  * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
 139  */
 140 #ifndef div64_u64
 141 u64 div64_u64(u64 dividend, u64 divisor)
 142 {
 143         u32 high = divisor >> 32;
 144         u64 quot;
 145
 146         if (high == 0) {
 147                 quot = div_u64(dividend, divisor);
 148         } else {
 149                 int n = 1 + fls(high);
 150                 quot = div_u64(dividend >> n, divisor >> n);
 151
 152                 if (quot != 0)
 153                         quot--;
 154                 if ((dividend - quot * divisor) >= divisor)
 155                         quot++;
 156         }
 157
 158         return quot;
 159 }
 160 EXPORT_SYMBOL(div64_u64);
 161 #endif
 162
 163 /**
 164  * div64_s64 - signed 64bit divide with 64bit divisor
 165  * @dividend:   64bit dividend
 166  * @divisor:    64bit divisor
 167  */
 168 #ifndef div64_s64
 169 s64 div64_s64(s64 dividend, s64 divisor)
 170 {
 171         s64 quot, t;
 172
 173         quot = div64_u64(abs(dividend), abs(divisor));
 174         t = (dividend ^ divisor) >> 63;
 175
 176         return (quot ^ t) - t;
 177 }
 178 EXPORT_SYMBOL(div64_s64);
 179 #endif
 180
 181 #endif /* BITS_PER_LONG == 32 */
 182
 183 /*
 184  * Iterative div/mod for use when dividend is not expected to be much
 185  * bigger than divisor.
 186  */
 187 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
 188 {
 189         return __iter_div_u64_rem(dividend, divisor, remainder);
 190 }
 191 EXPORT_SYMBOL(iter_div_u64_rem);