...
> Going the other way is similar:
>
> all_bits = low_bits + ((u64) high_bits << 16) << 16);
>
> and again, the compiler will recognize this idiom and do the right
> thing (and if 'all_bits' is only 32-bit, the compiler will optimize
> the high bit noise away).
On a 32bit system the compiler might not do the expected thing.
I had terrible trouble with the 32bit div_u64_u32() code I was
playing with getting the compiler to do 'something sensible' for
that.
I just couldn't get it to stop generating two 64bit values
(in two register pairs) and then oring them together.
I didn't try using a union - that might work.
On x64 the asm "A" (edx:eax) and "a" and "d" constraints will DTRT
but force the values into edx:eax which is ok if you are doing divides.
David
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