#undef BYTE_COPY_FWD
#define BYTE_COPY_FWD(dst_bp, src_bp, nbytes) \
do { \
int __d0; \
asm volatile(/* Clear the direction flag, so copying goes forward. */ \
"cld\n" \
/* Copy bytes. */ \
"rep\n" \
"movsb" : \
"=D" (dst_bp), "=S" (src_bp), "=c" (__d0) : \
"0" (dst_bp), "1" (src_bp), "2" (nbytes) : \
"memory"); \
} while (0)
#undef BYTE_COPY_BWD
#define BYTE_COPY_BWD(dst_ep, src_ep, nbytes) \
do \
{ \
int __d0; \
asm volatile(/* Set the direction flag, so copying goes backwards. */ \
"std\n" \
/* Copy bytes. */ \
"rep\n" \
"movsb\n" \
/* Clear the dir flag. Convention says it should be 0. */ \
"cld" : \
"=D" (dst_ep), "=S" (src_ep), "=c" (__d0) : \
"0" (dst_ep - 1), "1" (src_ep - 1), "2" (nbytes) : \
"memory"); \
dst_ep += 1; \
src_ep += 1; \
} while (0)
#undef WORD_COPY_FWD
#define WORD_COPY_FWD(dst_bp, src_bp, nbytes_left, nbytes) \
do \
{ \
int __d0; \
asm volatile(/* Clear the direction flag, so copying goes forward. */ \
"cld\n" \
/* Copy longwords. */ \
"rep\n" \
"movsl" : \
"=D" (dst_bp), "=S" (src_bp), "=c" (__d0) : \
"0" (dst_bp), "1" (src_bp), "2" ((nbytes) / 4) : \
"memory"); \
(nbytes_left) = (nbytes) % 4; \
} while (0)
#undef WORD_COPY_BWD
#define WORD_COPY_BWD(dst_ep, src_ep, nbytes_left, nbytes) \
do \
{ \
int __d0; \
asm volatile(/* Set the direction flag, so copying goes backwards. */ \
"std\n" \
/* Copy longwords. */ \
"rep\n" \
"movsl\n" \
/* Clear the dir flag. Convention says it should be 0. */ \
"cld" : \
"=D" (dst_ep), "=S" (src_ep), "=c" (__d0) : \
"0" (dst_ep - 4), "1" (src_ep - 4), "2" ((nbytes) / 4) : \
"memory"); \
dst_ep += 4; \
src_ep += 4; \
(nbytes_left) = (nbytes) % 4; \
} while (0)
单片机的C语言，定义了宏还内嵌了汇编。
这就是c啊，你哪句看不懂？