From 2c2ccdca74a2c2f1bd63a51ca6eb97f2a368f0f4 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Mon, 2 Aug 2021 21:46:19 +0300
Subject: [PATCH] opcode: optimize IsValid
MIME-Version: 1.0
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Map access costs much more than array access.

name       old time/op  new time/op  delta
IsValid-8  17.6ns ± 2%   1.1ns ± 2%  -93.68%  (p=0.008 n=5+5)
---
 pkg/vm/opcode/isvalid_test.go | 15 +++++++++++++++
 pkg/vm/opcode/opcode.go       | 12 ++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 pkg/vm/opcode/isvalid_test.go

diff --git a/pkg/vm/opcode/isvalid_test.go b/pkg/vm/opcode/isvalid_test.go
new file mode 100644
index 000000000..2361c4ee8
--- /dev/null
+++ b/pkg/vm/opcode/isvalid_test.go
@@ -0,0 +1,15 @@
+package opcode
+
+import (
+	"testing"
+)
+
+// IsValid() is called for every VM instruction.
+func BenchmarkIsValid(t *testing.B) {
+	// Just so that we don't always test the same opcode.
+	script := []Opcode{NOP, ADD, SYSCALL, APPEND, 0xff, 0xf0}
+	l := len(script)
+	for n := 0; n < t.N; n++ {
+		_ = IsValid(script[n%l])
+	}
+}
diff --git a/pkg/vm/opcode/opcode.go b/pkg/vm/opcode/opcode.go
index 3d24b7ea7..93b62e5cd 100644
--- a/pkg/vm/opcode/opcode.go
+++ b/pkg/vm/opcode/opcode.go
@@ -222,8 +222,16 @@ const (
 	CONVERT Opcode = 0xDB
 )
 
+var validCodes [256]bool
+
+func init() {
+	// We rely on stringer here, it has a map anyway.
+	for op := range _Opcode_map {
+		validCodes[int(op)] = true
+	}
+}
+
 // IsValid returns true if the opcode passed is valid (defined in the VM).
 func IsValid(op Opcode) bool {
-	_, ok := _Opcode_map[op] // We rely on stringer here, it has a map anyway.
-	return ok
+	return validCodes[int(op)]
 }