Why does AVX512-IFMA support only 52-bit ints?

Question

From the value we can infer that it uses the same components as double-precision floating-point hardware. But double has 53 bits of significand, so why is AVX512-IFMA limited to 52 bits? Sure the mantissa has only 52 bits and one bit is hidden, but it still contributes to the value and needs to be fed into the adder/multiplier/divider...

Answer 1

IEEE-754 double precision actually only has 52 explicitly stored bits, the 53rd bit (the most significant bit) is an implicit 1.