Tags: X86 L3 .
This is one of the hardest ever exercises at this website. What does this code do?
Hint: the function has been copypasted from the guts of GCC, but in fact, it is present almost in all modern compilers, though, in different forms, but calculating the same value(s). Its function is highly important.
Second hint: f(f(x))=x.
Optimizing GCC 5.4 x86
f: mov edx, 31 mov eax, 1 .L2: imul eax, edi imul edi, edi sub edx, 1 jne .L2 ret
More challenges: challenges.re; about solutions: challenges.re/#Solutions.