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 /**
  65  * div_s64_rem - signed 64bit divide with 64bit divisor and remainder
  66  * @dividend:   64bit dividend
  67  * @divisor:    64bit divisor
  68  * @remainder:  64bit remainder
  69  */
  70 #ifndef div_s64_rem
  71 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
  72 {
  73         u64 quotient;
  74
  75         if (dividend < 0) {
  76                 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
  77                 *remainder = -*remainder;
  78                 if (divisor > 0)
  79                         quotient = -quotient;
  80         } else {
  81                 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
  82                 if (divisor < 0)
  83                         quotient = -quotient;
  84         }
  85         return quotient;
  86 }
  87 EXPORT_SYMBOL(div_s64_rem);
  88 #endif
  89
  90 /**
  91  * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
  92  * @dividend:   64bit dividend
  93  * @divisor:    64bit divisor
  94  * @remainder:  64bit remainder
  95  *
  96  * This implementation is a comparable to algorithm used by div64_u64.
  97  * But this operation, which includes math for calculating the remainder,
  98  * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
  99  * systems.
 100  */
 101 #ifndef div64_u64_rem
 102 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
 103 {
 104         u32 high = divisor >> 32;
 105         u64 quot;
 106
 107         if (high == 0) {
 108                 u32 rem32;
 109                 quot = div_u64_rem(dividend, divisor, &rem32);
 110                 *remainder = rem32;
 111         } else {
 112                 int n = 1 + fls(high);
 113                 quot = div_u64(dividend >> n, divisor >> n);
 114
 115                 if (quot != 0)
 116                         quot--;
 117
 118                 *remainder = dividend - quot * divisor;
 119                 if (*remainder >= divisor) {
 120                         quot++;
 121                         *remainder -= divisor;
 122                 }
 123         }
 124
 125         return quot;
 126 }
 127 EXPORT_SYMBOL(div64_u64_rem);
 128 #endif
 129
 130 /**
 131  * div64_u64 - unsigned 64bit divide with 64bit divisor
 132  * @dividend:   64bit dividend
 133  * @divisor:    64bit divisor
 134  *
 135  * This implementation is a modified version of the algorithm proposed
 136  * by the book 'Hacker's Delight'.  The original source and full proof
 137  * can be found here and is available for use without restriction.
 138  *
 139  * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
 140  */
 141 #ifndef div64_u64
 142 u64 div64_u64(u64 dividend, u64 divisor)
 143 {
 144         u32 high = divisor >> 32;
 145         u64 quot;
 146
 147         if (high == 0) {
 148                 quot = div_u64(dividend, divisor);
 149         } else {
 150                 int n = 1 + fls(high);
 151                 quot = div_u64(dividend >> n, divisor >> n);
 152
 153                 if (quot != 0)
 154                         quot--;
 155                 if ((dividend - quot * divisor) >= divisor)
 156                         quot++;
 157         }
 158
 159         return quot;
 160 }
 161 EXPORT_SYMBOL(div64_u64);
 162 #endif
 163
 164 /**
 165  * div64_s64 - signed 64bit divide with 64bit divisor
 166  * @dividend:   64bit dividend
 167  * @divisor:    64bit divisor
 168  */
 169 #ifndef div64_s64
 170 s64 div64_s64(s64 dividend, s64 divisor)
 171 {
 172         s64 quot, t;
 173
 174         quot = div64_u64(abs(dividend), abs(divisor));
 175         t = (dividend ^ divisor) >> 63;
 176
 177         return (quot ^ t) - t;
 178 }
 179 EXPORT_SYMBOL(div64_s64);
 180 #endif
 181
 182 #endif /* BITS_PER_LONG == 32 */
 183
 184 /*
 185  * Iterative div/mod for use when dividend is not expected to be much
 186  * bigger than divisor.
 187  */
 188 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
 189 {
 190         return __iter_div_u64_rem(dividend, divisor, remainder);
 191 }
 192 EXPORT_SYMBOL(iter_div_u64_rem);