Best way to load a 64-bit integer to a double precision SSE2 register?
assembly, double, int64, sse, sse2
Solution
Your second option can be made to work, though it's a little unwieldy. I'll assume that your 64-bit number is initially in edx:eax.
cvtsi2sd xmm0, edx // high part * 2**-32
mulsd xmm0, [2**32 from mem] // high part
movsd xmm2, [2**52 from mem]
movd xmm1, eax
orpd xmm1, xmm2 // (double)(2*52 + low part as unsigned)
subsd xmm1, xmm2 // (double)(low part as unsigned)
addsd xmm0, xmm1 // (double)(high part + low part as unsigned)
All of the operations except for possibly the final one are exact, so this is correctly rounded. It should be noted that this conversion produces `-0.0` when the input is `0` and the `mxcsr` is set to round-to-minus-infinity. This would need to be addressed if it were being used in a runtime library for a compiler aiming to provide IEEE-754 conformance, but is not an issue for most usage.
Problem
What is the best/fastest way to load a 64-bit integer value in an `xmm` SSE2 register in 32-bit mode? In 64-bit mode, `cvtsi2sd` can be used, but in 32-bit mode, it supports only 32-bit integers. So far I haven't found much beyond: - use `fild`, `fstp` to stack then `movsd` to `xmm` register - load the high 32-bit portion, multiply by 2^32, add the low 32-bit First solution is slow, second solution might introduce precision loss (edit: and it is slow anyway, since the low 32 bit have to be converted as unsigned...) Any better approach?