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#include <stdio.h>
long rsum(long *start, long count) {
if (count <= 0)
return 0;
return *start + rsum(start + 1, count - 1);
}
int main() {
long nums[] = {1, 2, 3};
printf("%d\n", rsum(nums, 3));
}
/*
long rsum(long *start, long count)
start in %rdi, count in %rsi
test:
xorq %rax, %rax return = 0
andq %rsi, %rsi, Set CC again?
jle return Count <= 0, or jump
push %rbx keep original rbx around
mrmovq (%rdi), %rbx Get *start
irmovq $8,%r8 Constant 8
irmovq $1,%r9 Constant 1
addq %r8,%rdi start++
subq %r9,%rsi count--. Set CC
call rsum Recurse
addq %rbx, %rax Accumulate
popq %rbx Restore original rbx
return:
ret
*/
/*
0000000000001149 <rsum>:
1149: 48 85 f6 test %rsi,%rsi
114c: 7e 16 jle 1164 <rsum+0x1b>
114e: 53 push %rbx
114f: 48 8b 1f mov (%rdi),%rbx
1152: 48 83 ee 01 sub $0x1,%rsi
1156: 48 83 c7 08 add $0x8,%rdi
115a: e8 ea ff ff ff call 1149 <rsum>
115f: 48 01 d8 add %rbx,%rax
1162: 5b pop %rbx Return accumulated %rbx
1163: c3 ret
1164: b8 00 00 00 00 mov $0x0,%eax Return 0 after first test
1169: c3 ret
*/
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