lib/div64.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
   4  *
   5  * Based on former do_div() implementation from asm-parisc/div64.h:
   6  *      Copyright (C) 1999 Hewlett-Packard Co
   7  *      Copyright (C) 1999 David Mosberger-Tang <davidm@hpl.hp.com>
   8  *
   9  *
  10  * Generic C version of 64bit/32bit division and modulo, with
  11  * 64bit result and 32bit remainder.
  12  *
  13  * The fast case for (n>>32 == 0) is handled inline by do_div().
  14  *
  15  * Code generated for this function might be very inefficient
  16  * for some CPUs. __div64_32() can be overridden by linking arch-specific
  17  * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S
  18  * or by defining a preprocessor macro in arch/include/asm/div64.h.
  19  */
  20
  21 #include <linux/export.h>
  22 #include <linux/kernel.h>
  23 #include <linux/math64.h>
  24
  25 /* Not needed on 64bit architectures */
  26 #if BITS_PER_LONG == 32
  27
  28 #ifndef __div64_32
  29 uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
  30 {
  31         uint64_t rem = *n;
  32         uint64_t b = base;
  33         uint64_t res, d = 1;
  34         uint32_t high = rem >> 32;
  35
  36         /* Reduce the thing a bit first */
  37         res = 0;
  38         if (high >= base) {
  39                 high /= base;
  40                 res = (uint64_t) high << 32;
  41                 rem -= (uint64_t) (high*base) << 32;
  42         }
  43
  44         while ((int64_t)b > 0 && b < rem) {
  45                 b = b+b;
  46                 d = d+d;
  47         }
  48
  49         do {
  50                 if (rem >= b) {
  51                         rem -= b;
  52                         res += d;
  53                 }
  54                 b >>= 1;
  55                 d >>= 1;
  56         } while (d);
  57
  58         *n = res;
  59         return rem;
  60 }
  61 EXPORT_SYMBOL(__div64_32);
  62 #endif
  63
  64 #ifndef div_s64_rem
  65 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
  66 {
  67         u64 quotient;
  68
  69         if (dividend < 0) {
  70                 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
  71                 *remainder = -*remainder;
  72                 if (divisor > 0)
  73                         quotient = -quotient;
  74         } else {
  75                 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
  76                 if (divisor < 0)
  77                         quotient = -quotient;
  78         }
  79         return quotient;
  80 }
  81 EXPORT_SYMBOL(div_s64_rem);
  82 #endif
  83
  84 /**
  85  * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
  86  * @dividend:   64bit dividend
  87  * @divisor:    64bit divisor
  88  * @remainder:  64bit remainder
  89  *
  90  * This implementation is a comparable to algorithm used by div64_u64.
  91  * But this operation, which includes math for calculating the remainder,
  92  * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
  93  * systems.
  94  */
  95 #ifndef div64_u64_rem
  96 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
  97 {
  98         u32 high = divisor >> 32;
  99         u64 quot;
 100
 101         if (high == 0) {
 102                 u32 rem32;
 103                 quot = div_u64_rem(dividend, divisor, &rem32);
 104                 *remainder = rem32;
 105         } else {
 106                 int n = fls(high);
 107                 quot = div_u64(dividend >> n, divisor >> n);
 108
 109                 if (quot != 0)
 110                         quot--;
 111
 112                 *remainder = dividend - quot * divisor;
 113                 if (*remainder >= divisor) {
 114                         quot++;
 115                         *remainder -= divisor;
 116                 }
 117         }
 118
 119         return quot;
 120 }
 121 EXPORT_SYMBOL(div64_u64_rem);
 122 #endif
 123
 124 /**
 125  * div64_u64 - unsigned 64bit divide with 64bit divisor
 126  * @dividend:   64bit dividend
 127  * @divisor:    64bit divisor
 128  *
 129  * This implementation is a modified version of the algorithm proposed
 130  * by the book 'Hacker's Delight'.  The original source and full proof
 131  * can be found here and is available for use without restriction.
 132  *
 133  * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
 134  */
 135 #ifndef div64_u64
 136 u64 div64_u64(u64 dividend, u64 divisor)
 137 {
 138         u32 high = divisor >> 32;
 139         u64 quot;
 140
 141         if (high == 0) {
 142                 quot = div_u64(dividend, divisor);
 143         } else {
 144                 int n = fls(high);
 145                 quot = div_u64(dividend >> n, divisor >> n);
 146
 147                 if (quot != 0)
 148                         quot--;
 149                 if ((dividend - quot * divisor) >= divisor)
 150                         quot++;
 151         }
 152
 153         return quot;
 154 }
 155 EXPORT_SYMBOL(div64_u64);
 156 #endif
 157
 158 /**
 159  * div64_s64 - signed 64bit divide with 64bit divisor
 160  * @dividend:   64bit dividend
 161  * @divisor:    64bit divisor
 162  */
 163 #ifndef div64_s64
 164 s64 div64_s64(s64 dividend, s64 divisor)
 165 {
 166         s64 quot, t;
 167
 168         quot = div64_u64(abs(dividend), abs(divisor));
 169         t = (dividend ^ divisor) >> 63;
 170
 171         return (quot ^ t) - t;
 172 }
 173 EXPORT_SYMBOL(div64_s64);
 174 #endif
 175
 176 #endif /* BITS_PER_LONG == 32 */
 177
 178 /*
 179  * Iterative div/mod for use when dividend is not expected to be much
 180  * bigger than divisor.
 181  */
 182 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
 183 {
 184         return __iter_div_u64_rem(dividend, divisor, remainder);
 185 }
 186 EXPORT_SYMBOL(iter_div_u64_rem);