Copy src1 into dest before the masked vrangeps so that unmasked lanes
(normal/inf/NaN values) are preserved via merge-masking. Previously,
when the register allocator assigned different physical registers for
dest and src1, unmasked lanes would retain stale values from dest.
Tested with Intel SDE and AVX-512 cpu to verify.
Also shift unused FpRangeSign constants into bits [3:2] of the vrangeps
immediate, matching the Intel encoding. Only one used in the code was 0
so it was already correct by accident but using the others in the future
would produce incorrect results.
Use the `vptestnmd`-instruction to quickly test if the exponent bits of
each element is zero and put these results into a mask register. This
mask register can then be used to write `+0.0` or `-0.0` values
depending on the original value's sign-bit.
A masked `vrangeps` instruction is used to move zero-values into the effected
elements while preserving the sign-bit without having to touch memory.
