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kaityo256/collatz.cpp

Created January 25, 2019 01:43
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demons fly out of your nose
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collatz.cpp
// Modified from https://qiita.com/tkmtSo/items/de3148dd1dcb70f38d6a
#include <cstdio>
int collatz(int n) {
while (true) {
if (n == 1)
return 1;
if (n % 2 == 0) {
n /= 2;
} else {
n = 3 * n + 1;
}
}
}
int test(int n) {
return collatz(n);
}
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kaityo256 commented Jan 25, 2019 

$ clang++ -O3 -S collatz.cpp;c++filt <collatz.s  > collatz.clang.s

The function test returns 1 without any calculation!

test(int):                              ## @_Z4testi
        .cfi_startproc
## %bb.0:
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset %rbp, -16
        movq    %rsp, %rbp
        .cfi_def_cfa_register %rbp
        movl    $1, %eax
        popq    %rbp
        retq
        .cfi_endproc

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