Consider the following assembly code for a C for loop: loop: pushl %ebp movl %es

Question

Consider the following assembly code for a C for loop:

loop:
pushl %ebp
movl %esp,%ebp
movl 0x8(%ebp),%edx
movl %edx.%eax
addl 0xc(%ebp),%eax
leal 0xffffffff(%eax),%ecx
cmpl %ecx,%edx
jae .L4
.L6:
movb (%edx),%al
xorb (%ecx),%al
movb %al,(%edx)
xorb (%ecx),%al
movb %al,(%ecx)
xorb %al,(%edx)
incl %edx
decl %ecx
cmpl %ecx,%edx
jb .L6
.L4:
movl %ebp,%esp
popl %ebp
ret

Based on the assembly code above, fill in the blanks below in its corresponding C source code. (Note: you may only use the symbolic variables h, t and len in your expressions below----do not use register names.)

void loop(char *h, int len){
char *t;
for(__________; __________; h++, t--) {
________;
________;
________;
}
return;
}


Thank you soo much for taking the time to help "Life Saver"

Explanation / Answer

loop: pushl %ebp movl %esp,%ebp movl 0x8(%ebp),%edx # h movl %edx,%eax # h addl 0xc(%ebp),%eax # h + len leal 0xffffffff(%eax),%ecx # t = h + len - 1 cmpl %ecx,%edx # if h >= t jae .L4 # finshed .L6: movb (%edx),%al # *h xorb (%ecx),%al # *t ^ *h movb %al,(%edx) # *h = *t ^ *h xorb (%ecx),%al # *t ^ *h movb %al,(%ecx) # *t = *t ^ *h xorb %al,(%edx) # *h = *t ^ *h incl %edx # h++ decl %ecx # t-- cmpl %ecx,%edx # if h

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