From 19ad31dc527f1c8fbd152a68f8f2b0cf4ccd7fbc Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Tue, 7 Jun 2022 10:29:13 +0300
Subject: [PATCH] vm: optimize IsSignatureContract
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We use it a lot in (*Blockchain).IsTxStillRelevant().

name                   old time/op    new time/op    delta
IsSignatureContract-8    19.1ns ± 5%     1.2ns ± 4%  -93.81%  (p=0.000 n=10+10)

name                   old alloc/op   new alloc/op   delta
IsSignatureContract-8     0.00B          0.00B          ~     (all equal)

name                   old allocs/op  new allocs/op  delta
IsSignatureContract-8      0.00           0.00          ~     (all equal)
---
 pkg/vm/bench_test.go      |  9 +++++++++
 pkg/vm/contract_checks.go | 17 +++++++----------
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/pkg/vm/bench_test.go b/pkg/vm/bench_test.go
index c0403ea8b..d1ad21f24 100644
--- a/pkg/vm/bench_test.go
+++ b/pkg/vm/bench_test.go
@@ -48,3 +48,12 @@ func BenchmarkScriptPushPop(t *testing.B) {
 		})
 	}
 }
+
+func BenchmarkIsSignatureContract(t *testing.B) {
+	b64script := "DCED2eixa9myLTNF1tTN4xvhw+HRYVMuPQzOy5Xs4utYM25BVuezJw=="
+	script, err := base64.StdEncoding.DecodeString(b64script)
+	require.NoError(t, err)
+	for n := 0; n < t.N; n++ {
+		_ = IsSignatureContract(script)
+	}
+}
diff --git a/pkg/vm/contract_checks.go b/pkg/vm/contract_checks.go
index 1336765f4..51bb68040 100644
--- a/pkg/vm/contract_checks.go
+++ b/pkg/vm/contract_checks.go
@@ -118,17 +118,14 @@ func ParseSignatureContract(script []byte) ([]byte, bool) {
 		return nil, false
 	}
 
-	ctx := NewContext(script)
-	instr, param, err := ctx.Next()
-	if err != nil || instr != opcode.PUSHDATA1 || len(param) != 33 {
-		return nil, false
+	// We don't use Context for this simple case, it's more efficient this way.
+	if script[0] == byte(opcode.PUSHDATA1) && // PUSHDATA1
+		script[1] == 33 && // with a public key parameter
+		script[35] == byte(opcode.SYSCALL) && // and a CheckSig SYSCALL.
+		binary.LittleEndian.Uint32(script[36:]) == verifyInteropID {
+		return script[2:35], true
 	}
-	pub := param
-	instr, param, err = ctx.Next()
-	if err != nil || instr != opcode.SYSCALL || binary.LittleEndian.Uint32(param) != verifyInteropID {
-		return nil, false
-	}
-	return pub, true
+	return nil, false
 }
 
 // IsStandardContract checks whether the passed script is a signature or