Yes, this is for floating point multiplies. But internally, the FPU uses x86 extended-precision numbers, 80-bit floats, with 64 bits of significand and 15 expon

Yes, this is for floating point multiplies. But internally, the FPU uses x86 extended-precision numbers, 80-bit floats, with 64 bits of significand and 15 exponent bits. So the multiplier is dealing with 64-bit numbers, plus a few more bits to support rounding correctly. https://en.wikipedia.org/wiki/Extended_precision#x86_extended-precision_format https://en.wikipedia.org/wiki/Extended_precision#x86_extende...