core/vm: implement EIP-7939 - CLZ opcode (#31989)

https://eips.ethereum.org/EIPS/eip-7939

---------

Co-authored-by: spencer-tb <spencer@spencertaylorbrown.uk>
Co-authored-by: Felix Lange <fjl@twurst.com>

core/vm/eips.go

@@ -41,6 +41,7 @@ var activators = map[int]func(*JumpTable){
 	1153: enable1153,
 	4762: enable4762,
 	7702: enable7702,
+	7939: enable7939,
 }
 
 // EnableEIP enables the given EIP on the config.
@@ -293,6 +294,13 @@ func opBlobBaseFee(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext)
 	return nil, nil
 }
 
+// opCLZ implements the CLZ opcode (count leading zero bytes)
+func opCLZ(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([]byte, error) {
+	x := scope.Stack.peek()
+	x.SetUint64(256 - uint64(x.BitLen()))
+	return nil, nil
+}
+
 // enable4844 applies EIP-4844 (BLOBHASH opcode)
 func enable4844(jt *JumpTable) {
 	jt[BLOBHASH] = &operation{
@@ -303,6 +311,15 @@ func enable4844(jt *JumpTable) {
 	}
 }
 
+func enable7939(jt *JumpTable) {
+	jt[CLZ] = &operation{
+		execute:     opCLZ,
+		constantGas: GasFastestStep,
+		minStack:    minStack(1, 1),
+		maxStack:    maxStack(1, 1),
+	}
+}
+
 // enable7516 applies EIP-7516 (BLOBBASEFEE opcode)
 func enable7516(jt *JumpTable) {
 	jt[BLOBBASEFEE] = &operation{

core/vm/instructions_test.go

@@ -972,3 +972,43 @@ func TestPush(t *testing.T) {
 		}
 	}
 }
+
+func TestOpCLZ(t *testing.T) {
+	evm := NewEVM(BlockContext{}, nil, params.TestChainConfig, Config{})
+
+	tests := []struct {
+		inputHex string
+		want     uint64 // expected CLZ result
+	}{
+		{"0x0", 256},
+		{"0x1", 255},
+		{"0x6ff", 245},        // 0x6ff = 0b11011111111 (11 bits), so 256-11 = 245
+		{"0xffffffffff", 216}, // 40 bits, so 256-40 = 216
+		{"0x4000000000000000000000000000000000000000000000000000000000000000", 1},
+		{"0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 1},
+		{"0x8000000000000000000000000000000000000000000000000000000000000000", 0},
+		{"0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 0},
+	}
+	for _, tc := range tests {
+		// prepare a fresh stack and PC
+		stack := newstack()
+		pc := uint64(0)
+
+		// parse input
+		val := new(uint256.Int)
+		if err := val.SetFromHex(tc.inputHex); err != nil {
+			t.Fatal("invalid hex uint256:", tc.inputHex)
+		}
+
+		stack.push(val)
+		opCLZ(&pc, evm.interpreter, &ScopeContext{Stack: stack})
+
+		if gotLen := stack.len(); gotLen != 1 {
+			t.Fatalf("stack length = %d; want 1", gotLen)
+		}
+		result := stack.pop()
+		if got := result.Uint64(); got != tc.want {
+			t.Fatalf("clz(%q) = %d; want %d", tc.inputHex, got, tc.want)
+		}
+	}
+}

core/vm/interpreter.go

@@ -106,6 +106,8 @@ func NewEVMInterpreter(evm *EVM) *EVMInterpreter {
 	// If jump table was not initialised we set the default one.
 	var table *JumpTable
 	switch {
+	case evm.chainRules.IsOsaka:
+		table = &osakaInstructionSet
 	case evm.chainRules.IsVerkle:
 		// TODO replace with proper instruction set when fork is specified
 		table = &verkleInstructionSet

core/vm/jump_table.go

@@ -62,6 +62,7 @@ var (
 	cancunInstructionSet           = newCancunInstructionSet()
 	verkleInstructionSet           = newVerkleInstructionSet()
 	pragueInstructionSet           = newPragueInstructionSet()
+	osakaInstructionSet            = newOsakaInstructionSet()
 )
 
 // JumpTable contains the EVM opcodes supported at a given fork.
@@ -91,6 +92,12 @@ func newVerkleInstructionSet() JumpTable {
 	return validate(instructionSet)
 }
 
+func newOsakaInstructionSet() JumpTable {
+	instructionSet := newPragueInstructionSet()
+	enable7939(&instructionSet) // EIP-7939 (CLZ opcode)
+	return validate(instructionSet)
+}
+
 func newPragueInstructionSet() JumpTable {
 	instructionSet := newCancunInstructionSet()
 	enable7702(&instructionSet) // EIP-7702 Setcode transaction type

core/vm/jump_table_export.go

@@ -29,7 +29,7 @@ func LookupInstructionSet(rules params.Rules) (JumpTable, error) {
 	case rules.IsVerkle:
 		return newCancunInstructionSet(), errors.New("verkle-fork not defined yet")
 	case rules.IsOsaka:
-		return newPragueInstructionSet(), errors.New("osaka-fork not defined yet")
+		return newOsakaInstructionSet(), nil
 	case rules.IsPrague:
 		return newPragueInstructionSet(), nil
 	case rules.IsCancun:

core/vm/opcodes.go

@@ -62,6 +62,7 @@ const (
 	SHL    OpCode = 0x1b
 	SHR    OpCode = 0x1c
 	SAR    OpCode = 0x1d
+	CLZ    OpCode = 0x1e
 )
 
 // 0x20 range - crypto.
@@ -282,6 +283,7 @@ var opCodeToString = [256]string{
 	SHL:    "SHL",
 	SHR:    "SHR",
 	SAR:    "SAR",
+	CLZ:    "CLZ",
 	ADDMOD: "ADDMOD",
 	MULMOD: "MULMOD",
 
@@ -484,6 +486,7 @@ var stringToOp = map[string]OpCode{
 	"SHL":             SHL,
 	"SHR":             SHR,
 	"SAR":             SAR,
+	"CLZ":             CLZ,
 	"ADDMOD":          ADDMOD,
 	"MULMOD":          MULMOD,
 	"KECCAK256":       KECCAK256,