root/include/asm-x86/div64.h

INCLUDED FROM

DEFINITIONS

1. div_u64_rem

#ifndef ASM_X86__DIV64_H
#define ASM_X86__DIV64_H

#ifdef CONFIG_X86_32

#include <linux/types.h>

/*
 * do_div() is NOT a C function. It wants to return
 * two values (the quotient and the remainder), but
 * since that doesn't work very well in C, what it
 * does is:
 *
 * - modifies the 64-bit dividend _in_place_
 * - returns the 32-bit remainder
 *
 * This ends up being the most efficient "calling
 * convention" on x86.
 */
#define do_div(n, base)                                         \
({                                                              \
        unsigned long __upper, __low, __high, __mod, __base;    \
        __base = (base);                                        \
        asm("":"=a" (__low), "=d" (__high) : "A" (n));          \
        __upper = __high;                                       \
        if (__high) {                                           \
                __upper = __high % (__base);                    \
                __high = __high / (__base);                     \
        }                                                       \
        asm("divl %2":"=a" (__low), "=d" (__mod)                \
            : "rm" (__base), "0" (__low), "1" (__upper));       \
        asm("":"=A" (n) : "a" (__low), "d" (__high));           \
        __mod;                                                  \
})

static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
{
        union {
                u64 v64;
                u32 v32[2];
        } d = { dividend };
        u32 upper;

        upper = d.v32[1];
        d.v32[1] = 0;
        if (upper >= divisor) {
                d.v32[1] = upper / divisor;
                upper %= divisor;
        }
        asm ("divl %2" : "=a" (d.v32[0]), "=d" (*remainder) :
                "rm" (divisor), "0" (d.v32[0]), "1" (upper));
        return d.v64;
}
#define div_u64_rem     div_u64_rem

#else
# include <asm-generic/div64.h>
#endif /* CONFIG_X86_32 */

#endif /* ASM_X86__DIV64_H */