On 3/13/2025 9:36 AM, H. Peter Anvin wrote: > On March 13, 2025 9:24:38 AM PDT, Yury Norov <yury.norov@xxxxxxxxx> wrote: >> 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 <jacob.e.keller@xxxxxxxxx> wrote: >> >> [...] >> >>>> 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 > > The x86 implementation, no, but there will be plenty of others having that exact definition. Makes sense to stick with that existing convention then. Enough to convince me. Thanks, Jake
