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

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