noncliff: improve performance of _allthreesumtozero (#377)

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Co-authored-by: Stefan Krastanov <[email protected]>

Author: Fe-r-oz

src/nonclifford.jl

@@ -161,9 +161,13 @@ function expect(p::PauliOperator, s::GeneralizedStabilizer) # TODO optimize
 end
 
 """Same as `all(==(0), (a.+b.+c) .% 2)`"""
-function _allthreesumtozero(a,b,c) # TODO consider using bitpacking and SIMD xor with less eager shortcircuiting -- probably would be much faster
-    @inbounds @simd for i in 1:length(a)
-        iseven(a[i]+b[i]+c[i]) || return false
+function _allthreesumtozero(a,b,c)
+    n = length(a)
+    @inbounds @simd for i in 1:n
+        odd = (a[i]+b[i]+c[i]) & 1
+        if odd != 0
+            return false
+        end
     end
     true
 end