PMOVMSKB/BSF/POPCNT takes serious wizardry, but instructions like PCLMULLQLQDQ make you feel like Gandalf. It's defined: pair clmul(uint64_t a, uint64_t b)

PMOVMSKB/BSF/POPCNT takes serious wizardry, but instructions like PCLMULLQLQDQ make you feel like Gandalf. It's defined: pair clmul(uint64_t a, uint64_t b) { uint64_t t, x = 0, y = 0; if (a && b) { if (bsr(a) < bsr(b)) t = a, a = b, b = t; /* optional */ for (t = 0; b; a <<= 1, b >>= 1) { if (b & 1) x ^= a, y ^= t; t = t << 1 | a >> 63; } } return (pair){x, y}; } There's a famous paper on how it can perform polynomial division at 40gbps. It's really cool that it has practical applications in things like CSV too. https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-crc-computation-generic-polynomials-pclmulqdq-paper.pdf https://www.intel.com/content/dam/www/public/us/en/documents...