Merge pull request #530 from TheHippo/avx2-popcount

AVX2 popcount

Author: lemire

popcnt_amd64.s

@@ -0,0 +1,67 @@
+//go:build amd64 && !appengine
+// +build amd64,!appengine
+
+package roaring
+
+// The functions below are implemented in popcnt_avx2_amd64.s using AVX2.
+// They are only used when the CPU supports AVX2 (see useAVX2); otherwise the
+// pure-Go fallbacks in popcnt_slices.go are used. This keeps behavior identical
+// on every target: appengine and non-amd64 builds compile popcnt_generic.go
+// instead, and amd64 CPUs without AVX2 take the scalar path at runtime.
+
+//go:noescape
+func _hasAVX2() bool
+
+//go:noescape
+func _popcntSliceAVX2(s []uint64) uint64
+
+//go:noescape
+func _popcntMaskSliceAVX2(s, m []uint64) uint64
+
+//go:noescape
+func _popcntAndSliceAVX2(s, m []uint64) uint64
+
+//go:noescape
+func _popcntOrSliceAVX2(s, m []uint64) uint64
+
+//go:noescape
+func _popcntXorSliceAVX2(s, m []uint64) uint64
+
+// useAVX2 selects the AVX2 assembly implementations when the running CPU
+// supports AVX2. It is evaluated once at package initialization.
+var useAVX2 = _hasAVX2()
+
+func popcntSlice(s []uint64) uint64 {
+	if useAVX2 {
+		return _popcntSliceAVX2(s)
+	}
+	return popcntSliceGo(s)
+}
+
+func popcntMaskSlice(s, m []uint64) uint64 {
+	if useAVX2 {
+		return _popcntMaskSliceAVX2(s, m)
+	}
+	return popcntMaskSliceGo(s, m)
+}
+
+func popcntAndSlice(s, m []uint64) uint64 {
+	if useAVX2 {
+		return _popcntAndSliceAVX2(s, m)
+	}
+	return popcntAndSliceGo(s, m)
+}
+
+func popcntOrSlice(s, m []uint64) uint64 {
+	if useAVX2 {
+		return _popcntOrSliceAVX2(s, m)
+	}
+	return popcntOrSliceGo(s, m)
+}
+
+func popcntXorSlice(s, m []uint64) uint64 {
+	if useAVX2 {
+		return _popcntXorSliceAVX2(s, m)
+	}
+	return popcntXorSliceGo(s, m)
+}