From b9bf3afbb52aebcc0f93df55b55ec0f0f521b1ab Mon Sep 17 00:00:00 2001 From: Mike Vink Date: Sun, 16 Feb 2025 18:21:50 +0100 Subject: add some practice problems from 4 --- 4/practice_problem_4_4_rsum.c | 50 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 4/practice_problem_4_4_rsum.c (limited to '4/practice_problem_4_4_rsum.c') diff --git a/4/practice_problem_4_4_rsum.c b/4/practice_problem_4_4_rsum.c new file mode 100644 index 0000000..44960e6 --- /dev/null +++ b/4/practice_problem_4_4_rsum.c @@ -0,0 +1,50 @@ +#include + +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 : + 1149: 48 85 f6 test %rsi,%rsi + 114c: 7e 16 jle 1164 + + 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 + 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 +*/ -- cgit v1.2.3