Steinar H. Gunderson: Decompilation patterns, part 17: Loop rotation

Occasionally, you'll see code like this (after initial cleanup): var_v0_2 = crc & 0x80000000; do { if (var_v0_2 != 0) { crc = (crc << 1) ^ 0x1EDC6F41; } else { crc <<= 1; } var_a0 += 1; var_v0_2 = crc & 0x80000000; } while (var_a0 < 8U); The thing with var_v0_2 is unnatural. GCC sometimes does these loop rotation tricks, seemingly to save registers (don't ask me how exactly it does). You want to un-rotate back into: do {…

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