preallocate a few arrays.

When we do append loops, make an educated guess as to the size and make an array
with that capacity to avoid extra copying.

Doesn't affect the speed of the tests, over 4 runs the difference was lost in
the noise.

opcode.go

@@ -688,7 +688,15 @@ func (pop *parsedOpcode) print(oneline bool) string {
 }
 
 func (pop *parsedOpcode) bytes() []byte {
-	retbytes := []byte{pop.opcode.value}
+	var retbytes []byte
+	if pop.opcode.length > 0 {
+		retbytes = make([]byte, 1, pop.opcode.length)
+	} else {
+		retbytes = make([]byte, 1, 1 + len(pop.data) -
+			pop.opcode.length)
+	}
+
+	retbytes[0] = pop.opcode.value
 	if pop.opcode.length == 1 {
 		return retbytes
 	}
@@ -708,11 +716,7 @@ func (pop *parsedOpcode) bytes() []byte {
 		}
 	}
 
-	for i := range pop.data {
+	return append(retbytes, pop.data...)
-		retbytes = append(retbytes, pop.data[i])
-	}
-
-	return retbytes
 }
 
 // opcode implementation functions from here

script.go

@@ -274,7 +274,7 @@ func parseScript(script []byte) ([]parsedOpcode, error) {
 // template list for testing purposes. On error we return the list of parsed
 // opcodes so far.
 func parseScriptTemplate(script []byte, opcodemap map[byte]*opcode) ([]parsedOpcode, error) {
-	retScript := []parsedOpcode{}
+	retScript := make([]parsedOpcode, 0, len(script))
 	for i := 0; i < len(script); {
 		instr := script[i]
 		op, ok := opcodemap[instr]
@@ -329,7 +329,7 @@ func parseScriptTemplate(script []byte, opcodemap map[byte]*opcode) ([]parsedOpc
 // unparseScript reversed the action of parseScript and returns the
 // parsedOpcodes as a list of bytes
 func unparseScript(pops []parsedOpcode) []byte {
-	script := []byte{}
+	script := make([]byte, 0, len(pops))
 	for _, pop := range pops {
 		script = append(script, pop.bytes()...)
 	}
@@ -574,7 +574,7 @@ func (s *Script) subScript() []parsedOpcode {
 // removeOpcode will remove any opcode matching ``opcode'' from the opcode
 // stream in pkscript
 func removeOpcode(pkscript []parsedOpcode, opcode byte) []parsedOpcode {
-	retScript := []parsedOpcode{}
+	retScript := make([]parsedOpcode, 0, len(pkscript))
 	for _, pop := range pkscript {
 		if pop.opcode.value != opcode {
 			retScript = append(retScript, pop)
@@ -586,7 +586,7 @@ func removeOpcode(pkscript []parsedOpcode, opcode byte) []parsedOpcode {
 // removeOpcodeByData will return the pkscript minus any opcodes that would
 // push the data in ``data'' to the stack.
 func removeOpcodeByData(pkscript []parsedOpcode, data []byte) []parsedOpcode {
-	retScript := []parsedOpcode{}
+	retScript := make([]parsedOpcode, 0, len(pkscript))
 	for _, pop := range pkscript {
 		if !bytes.Equal(pop.data, data) {
 			retScript = append(retScript, pop)

test_coverage.txt

@@ -2,13 +2,13 @@
 github.com/conformal/btcscript/address.go	 scriptToAddressTemplate	 100.00% (58/58)
 github.com/conformal/btcscript/script.go	 Script.Step			 100.00% (37/37)
 github.com/conformal/btcscript/script.go	 parseScriptTemplate		 100.00% (30/30)
-github.com/conformal/btcscript/script.go	 NewScript			 100.00% (19/19)
+github.com/conformal/btcscript/script.go	 NewScript			 100.00% (18/18)
 github.com/conformal/btcscript/stack.go		 asInt				 100.00% (18/18)
 github.com/conformal/btcscript/stack.go		 fromInt			 100.00% (14/14)
+github.com/conformal/btcscript/opcode.go	 parsedOpcode.bytes		 100.00% (14/14)
 github.com/conformal/btcscript/opcode.go	 opcodeWithin			 100.00% (13/13)
-github.com/conformal/btcscript/script.go	 GetPreciseSigOpCount		 100.00% (13/13)
 github.com/conformal/btcscript/script.go	 isMultiSig			 100.00% (13/13)
-github.com/conformal/btcscript/opcode.go	 parsedOpcode.bytes		 100.00% (12/12)
+github.com/conformal/btcscript/script.go	 GetPreciseSigOpCount		 100.00% (13/13)
 github.com/conformal/btcscript/stack.go		 Stack.nipN			 100.00% (12/12)
 github.com/conformal/btcscript/opcode.go	 parsedOpcode.print		 100.00% (12/12)
 github.com/conformal/btcscript/opcode.go	 opcodeNotIf			 100.00% (11/11)
@@ -138,9 +138,9 @@ github.com/conformal/btcscript/opcode.go	 opcodeCheckMultiSig		 98.21% (55/56)
 github.com/conformal/btcscript/opcode.go	 opcodeCheckSig			 96.15% (25/26)
 github.com/conformal/btcscript/script.go	 Script.CheckErrorCondition	 78.57% (11/14)
 github.com/conformal/btcscript/opcode.go	 opcodeCheckSigVerify		 75.00% (3/4)
-github.com/conformal/btcscript/script.go	 Script.calcScriptHash		 71.43% (25/35)
+github.com/conformal/btcscript/script.go	 Script.calcScriptHash		 64.10% (25/39)
 github.com/conformal/btcscript/script.go	 Script.Execute			 44.44% (8/18)
 github.com/conformal/btcscript/log.go		 SetLogWriter			 0.00% (0/7)
 github.com/conformal/btcscript/log.go		 logClosure.String		 0.00% (0/1)
-github.com/conformal/btcscript			 --------------------------	 96.34% (896/930)
+github.com/conformal/btcscript			 --------------------------	 95.94% (897/935)