linux/include/asm-x86/string_64.h

#ifndef ASM_X86__STRING_64_H
#define ASM_X86__STRING_64_H

#ifdef __KERNEL__

/* Written 2002 by Andi Kleen */

/* Only used for special circumstances. Stolen from i386/string.h */
static __always_inline void *__inline_memcpy(void *to, const void *from, size_t n)
{
	unsigned long d0, d1, d2;
	asm volatile("rep ; movsl\n\t"
		     "testb $2,%b4\n\t"
		     "je 1f\n\t"
		     "movsw\n"
		     "1:\ttestb $1,%b4\n\t"
		     "je 2f\n\t"
		     "movsb\n"
		     "2:"
		     : "=&c" (d0), "=&D" (d1), "=&S" (d2)
		     : "0" (n / 4), "q" (n), "1" ((long)to), "2" ((long)from)
		     : "memory");
	return to;
}

/* Even with __builtin_ the compiler may decide to use the out of line
   function. */

#define __HAVE_ARCH_MEMCPY 1
#if (__GNUC__ == 4 && __GNUC_MINOR__ >= 3) || __GNUC__ > 4
extern void *memcpy(void *to, const void *from, size_t len);
#else
extern void *__memcpy(void *to, const void *from, size_t len);
#define memcpy(dst, src, len)					\
({								\
	size_t __len = (len);					\
	void *__ret;						\
	if (__builtin_constant_p(len) && __len >= 64)		\
		__ret = __memcpy((dst), (src), __len);		\
	else							\
		__ret = __builtin_memcpy((dst), (src), __len);	\
	__ret;							\
})
#endif

#define __HAVE_ARCH_MEMSET
void *memset(void *s, int c, size_t n);

#define __HAVE_ARCH_MEMMOVE
void *memmove(void *dest, const void *src, size_t count);

int memcmp(const void *cs, const void *ct, size_t count);
size_t strlen(const char *s);
char *strcpy(char *dest, const char *src);
char *strcat(char *dest, const char *src);
int strcmp(const char *cs, const char *ct);

#endif /* __KERNEL__ */

#endif /* ASM_X86__STRING_64_H */