source: trunk/packages/xen-3.1/xen-3.1/xen/include/asm-x86/div64.h @ 34

#ifndef __I386_DIV64
#define __I386_DIV64

#include <xen/types.h>

#if BITS_PER_LONG == 64

# define do_div(n,base) ({                                      \
        uint32_t __base = (base);                               \
        uint32_t __rem;                                         \
        __rem = ((uint64_t)(n)) % __base;                       \
        (n) = ((uint64_t)(n)) / __base;                         \
        __rem;                                                  \
 })

#else

/*
 * 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; \
})

#endif

#endif