bits.Mul64(a, b) lo, c := bits.Add64(lo, v.lo, 0) hi, _ = bits.Add64(hi, v.hi, c) return uint128{lo, hi} } // mul19 returns v * 19. func mul19(v uint64) uint64 { // Using this approach seems to yield better optimizations than *19. return v + (v+v<<3)<<1 } // addMul19 returns v + 19 * a * b, where a and b are at most 52 bits. func addMul19(v uint128, a, b uint64) uint128 { hi, lo := bits.Mul64(mul19(a), b) lo, c := bits.Add64(lo, v.lo, 0) hi, _ = bits.Add64(hi, v.hi, c) return uint128{lo, hi} } // addMul38...