root/arch/x86/include/asm/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>
#include <linux/log2.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);                                        \
        if (__builtin_constant_p(__base) && is_power_of_2(__base)) { \
                __mod = n & (__base - 1);                       \
                n >>= ilog2(__base);                            \
        } else {                                                \
                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 */