LXR linux/arch/x86/include/asm/div64.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef _ASM_X86_DIV64_H
   3#define _ASM_X86_DIV64_H
   4
   5#ifdef CONFIG_X86_32
   6
   7#include <linux/types.h>
   8#include <linux/log2.h>
   9
  10/*
  11 * do_div() is NOT a C function. It wants to return
  12 * two values (the quotient and the remainder), but
  13 * since that doesn't work very well in C, what it
  14 * does is:
  15 *
  16 * - modifies the 64-bit dividend _in_place_
  17 * - returns the 32-bit remainder
  18 *
  19 * This ends up being the most efficient "calling
  20 * convention" on x86.
  21 */
  22#define do_div(n, base)                                         \
  23({                                                              \
  24        unsigned long __upper, __low, __high, __mod, __base;    \
  25        __base = (base);                                        \
  26        if (__builtin_constant_p(__base) && is_power_of_2(__base)) { \
  27                __mod = n & (__base - 1);                       \
  28                n >>= ilog2(__base);                            \
  29        } else {                                                \
  30                asm("" : "=a" (__low), "=d" (__high) : "A" (n));\
  31                __upper = __high;                               \
  32                if (__high) {                                   \
  33                        __upper = __high % (__base);            \
  34                        __high = __high / (__base);             \
  35                }                                               \
  36                asm("divl %2" : "=a" (__low), "=d" (__mod)      \
  37                        : "rm" (__base), "0" (__low), "1" (__upper));   \
  38                asm("" : "=A" (n) : "a" (__low), "d" (__high)); \
  39        }                                                       \
  40        __mod;                                                  \
  41})
  42
  43static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
  44{
  45        union {
  46                u64 v64;
  47                u32 v32[2];
  48        } d = { dividend };
  49        u32 upper;
  50
  51        upper = d.v32[1];
  52        d.v32[1] = 0;
  53        if (upper >= divisor) {
  54                d.v32[1] = upper / divisor;
  55                upper %= divisor;
  56        }
  57        asm ("divl %2" : "=a" (d.v32[0]), "=d" (*remainder) :
  58                "rm" (divisor), "0" (d.v32[0]), "1" (upper));
  59        return d.v64;
  60}
  61#define div_u64_rem     div_u64_rem
  62
  63static inline u64 mul_u32_u32(u32 a, u32 b)
  64{
  65        u32 high, low;
  66
  67        asm ("mull %[b]" : "=a" (low), "=d" (high)
  68                         : [a] "a" (a), [b] "rm" (b) );
  69
  70        return low | ((u64)high) << 32;
  71}
  72#define mul_u32_u32 mul_u32_u32
  73
  74#else
  75# include <asm-generic/div64.h>
  76#endif /* CONFIG_X86_32 */
  77
  78#endif /* _ASM_X86_DIV64_H */
  79