feat(const_eval): impl. countOneBits

CHANGELOG.md

@@ -69,6 +69,7 @@ Bottom level categories:
     - [#5098](https://github.com/gfx-rs/wgpu/pull/5098) by @ErichDonGubler:
         - `ceil`
         - `countLeadingZeros`
+        - `countOneBits`
         - `floor`
 - Eager release of GPU resources comes from device.trackers. By @bradwerth in [#5075](https://github.com/gfx-rs/wgpu/pull/5075)
 - `wgpu-types`'s `trace` and `replay` features have been replaced by the `serde` feature. By @KirmesBude in [#5149](https://github.com/gfx-rs/wgpu/pull/5149)

naga/src/proc/constant_evaluator.rs

@@ -886,6 +886,15 @@ impl<'a> ConstantEvaluator<'a> {
                         .expect("bit count overflowed 32 bits, somehow!?")])
                 })
             }
+            crate::MathFunction::CountOneBits => {
+                component_wise_concrete_int!(self, span, [arg], |e| {
+                    #[allow(clippy::useless_conversion)]
+                    Ok([e
+                        .count_ones()
+                        .try_into()
+                        .expect("bit count overflowed 32 bits, somehow!?")])
+                })
+            }
             crate::MathFunction::Floor => {
                 component_wise_float!(self, span, [arg], |e| { Ok([e.floor()]) })
             }