div64.h

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#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 */