script: short-circuit GetLegacySigOpCount for known scripts

l0rinc · l0rinc · commit bde1fc128944 · 2025-05-19T11:12:39.000+02:00
&gt; build/bin/bench_bitcoin -filter='SigOpsBlockBench' --min-time=1000

|           ns/sigops |            sigops/s |    err% |      ins/sigops |      cyc/sigops |    IPC |     bra/sigops |   miss% |     total | benchmark
|--------------------:|--------------------:|--------:|----------------:|----------------:|-------:|---------------:|--------:|----------:|:----------
|               58.43 |       17,115,813.09 |    0.1% |          354.20 |          209.79 |  1.688 |          89.46 |    2.8% |     10.83 | `SigOpsBlockBench`
diff --git a/src/script/script.cpp b/src/script/script.cpp
@@ -186,24 +186,35 @@ static constexpr std::pair<unsigned int, unsigned int> DecodePushData(
 
 unsigned int CScript::GetLegacySigOpCount(bool fAccurate) const
 {
-    unsigned int n = 0;
-    const_iterator pc = begin();
-    opcodetype lastOpcode = OP_INVALIDOPCODE;
-    while (pc < end())
-    {
-        opcodetype opcode;
-        if (!GetOp(pc, opcode))
-            break;
-        if (opcode == OP_CHECKSIG || opcode == OP_CHECKSIGVERIFY)
-            n++;
-        else if (opcode == OP_CHECKMULTISIG || opcode == OP_CHECKMULTISIGVERIFY)
-        {
-            if (fAccurate && lastOpcode >= OP_1 && lastOpcode <= OP_16)
-                n += DecodeOP_N(lastOpcode);
-            else
+    switch (size()) {
+    case 0: return 0;
+    case 4: if (IsPayToAnchor()) return 0; else break;
+    case 22: if (IsPayToWitnessPubKeyHash()) return 0; else break;
+    case 23: if (IsPayToScriptHash()) return 0; else break;
+    case 25: if (IsPayToPubKeyHash()) return 1; else break;
+    case 34: if (IsPayToTaproot() || IsPayToWitnessScriptHash()) return 0; else break;
+    case 35: if (IsCompressedPayToPubKey()) return 1; else break;
+    case 67: if (IsUncompressedPayToPubKey()) return 1; else break;
+    }
+
+    unsigned int n{0};
+    opcodetype prev{OP_INVALIDOPCODE};
+    for (const_iterator pc{begin()}, pc_end{end()}; pc < pc_end;) {
+        const auto opcode{static_cast<opcodetype>(*pc++)};
+        if (opcode <= OP_PUSHDATA4) {
+            auto [size_bytes, data_bytes]{DecodePushData(opcode, pc, pc_end - pc)};
+            if (data_bytes == DECODE_ERR) break;
+            pc += size_bytes + data_bytes;
+        } else if (opcode == OP_CHECKSIG || opcode == OP_CHECKSIGVERIFY) {
+            ++n;
+        } else if (opcode == OP_CHECKMULTISIG || opcode == OP_CHECKMULTISIGVERIFY) {
+            if (fAccurate && IsSmallInteger(prev)) {
+                n += DecodeOP_N(prev);
+            } else {
                 n += MAX_PUBKEYS_PER_MULTISIG;
+            }
         }
-        lastOpcode = opcode;
+        if (fAccurate) prev = opcode;
     }
     return n;
 }
diff --git a/src/script/script.h b/src/script/script.h
@@ -535,6 +535,12 @@ class CScript : public CScriptBase
         return (opcodetype)(OP_1+n-1);
     }
 
+    /** Test for "small positive integer" script opcodes - OP_1 through OP_16. */
+    static constexpr bool IsSmallInteger(opcodetype opcode)
+    {
+        return opcode >= OP_1 && opcode <= OP_16;
+    }
+
     /**
      * Pre-version-0.6, Bitcoin always counted CHECKMULTISIGs
      * as 20 sigops. With pay-to-script-hash, that changed:
diff --git a/src/script/solver.cpp b/src/script/solver.cpp
@@ -55,18 +55,12 @@ static bool MatchPayToPubkeyHash(const CScript& script, valtype& pubkeyhash)
     return false;
 }
 
-/** Test for "small positive integer" script opcodes - OP_1 through OP_16. */
-static constexpr bool IsSmallInteger(opcodetype opcode)
-{
-    return opcode >= OP_1 && opcode <= OP_16;
-}
-
 /** Retrieve a minimally-encoded number in range [min,max] from an (opcode, data) pair,
  *  whether it's OP_n or through a push. */
 static std::optional<int> GetScriptNumber(opcodetype opcode, valtype data, int min, int max)
 {
     int count;
-    if (IsSmallInteger(opcode)) {
+    if (CScript::IsSmallInteger(opcode)) {
         count = CScript::DecodeOP_N(opcode);
     } else if (IsPushdataOp(opcode)) {
         if (!CheckMinimalPush(data, opcode)) return {};
