From 3fb8e60a1dd3709238a920800a539957179180d7 Mon Sep 17 00:00:00 2001
From: Jille Timmermans <jille@quis.cx>
Date: Fri, 12 Jul 2024 19:59:46 +0200
Subject: [PATCH] Check if the current CPU has AVX2 support

If built with GOAMD64=v3+ we know it is and resolve it compile time
---
 detect_axv2_always.go  | 7 +++++++
 detect_axv2_never.go   | 7 +++++++
 detect_axv2_runtime.go | 9 +++++++++
 go.mod                 | 2 ++
 go.sum                 | 2 ++
 lib.go                 | 6 +++++-
 6 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 detect_axv2_always.go
 create mode 100644 detect_axv2_never.go
 create mode 100644 detect_axv2_runtime.go

diff --git a/detect_axv2_always.go b/detect_axv2_always.go
new file mode 100644
index 0000000..3b63bd8
--- /dev/null
+++ b/detect_axv2_always.go
@@ -0,0 +1,7 @@
+//go:build amd64.v3
+
+package and
+
+func hasAVX2() bool {
+	return true
+}
diff --git a/detect_axv2_never.go b/detect_axv2_never.go
new file mode 100644
index 0000000..5f3cef5
--- /dev/null
+++ b/detect_axv2_never.go
@@ -0,0 +1,7 @@
+//go:build !amd64
+
+package and
+
+func hasAVX2() bool {
+	return false
+}
diff --git a/detect_axv2_runtime.go b/detect_axv2_runtime.go
new file mode 100644
index 0000000..5850d8d
--- /dev/null
+++ b/detect_axv2_runtime.go
@@ -0,0 +1,9 @@
+//go:build amd64 && !amd64.v3
+
+package and
+
+import "golang.org/x/sys/cpu"
+
+func hasAVX2() bool {
+	return cpu.X86.HasAVX2
+}
diff --git a/go.mod b/go.mod
index 4eb648e..ac4ad79 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
 module github.com/bwesterb/go-and
 
 go 1.22.0
+
+require golang.org/x/sys v0.22.0
diff --git a/go.sum b/go.sum
index e69de29..96f003d 100644
--- a/go.sum
+++ b/go.sum
@@ -0,0 +1,2 @@
+golang.org/x/sys v0.22.0 h1:RI27ohtqKCnwULzJLqkv897zojh5/DwS/ENaMzUOaWI=
+golang.org/x/sys v0.22.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
diff --git a/lib.go b/lib.go
index 1b608fd..9e71a3f 100644
--- a/lib.go
+++ b/lib.go
@@ -13,7 +13,11 @@ func And(dst, a, b []byte) {
 		panic("lengths of a, b and dst must be equal")
 	}
 
-	and(dst, a, b)
+	if hasAVX2() {
+		and(dst, a, b)
+		return
+	}
+	andGeneric(dst, a, b)
 }
 
 func andGeneric(dst, a, b []byte) {