On Wed, Mar 12, 2025 at 05:09:16PM -0700, H. Peter Anvin wrote:

On March 12, 2025 4:56:31 PM PDT, Jacob Keller [off-list ref] wrote:

[...]

quoted

This is really a question of whether you expect odd or even parity as
the "true" value. I think that would depend on context, and we may not
reach a good consensus.

I do agree that my brain would jump to "true is even, false is odd".
However, I also agree returning the value as 0 for even and 1 for odd
kind of made sense before, and updating this to be a bool and then
requiring to switch all the callers is a bit obnoxious...

Odd = 1 = true is the only same definition. It is a bitwise XOR, or sum mod 1.

The x86 implementation will be "popcnt(val) & 1", right? So if we
choose to go with odd == false, we'll have to add an extra negation.
So because it's a purely conventional thing, let's just pick a simpler
one?

Compiler's builtin parity() returns 1 for odd.

Thanks,
Yury