fix multi-byte bug in previous.

Use the right offset when working out if we should mask off the sign bit.
Add more tests that would have caught this case.

stack.go

@@ -33,7 +33,7 @@ func asInt(v []byte) *big.Int {
 	intArray := make([]byte, len(v))
 	for i := range v {
 		// Mask off the sign bit without changing original array.
-		if i == 0 && start == 0 && negative {
+		if i == len(v) -1 && start == 0 && negative {
 			intArray[len(v)-i -1] = v[i] & 0x7f
 		} else {
 			intArray[len(v)-i-1] = v[i]

stack_test.go

@@ -236,6 +236,22 @@ var stackTests = []stackTest{
 		nil,
 		[][]byte{},
 	},
+	{
+		"popInt -1",
+		[][]byte{{0x81}},
+		func(stack *btcscript.Stack) error {
+			v, err := stack.PopInt()
+			if err != nil {
+				return err
+			}
+			if v.Cmp(big.NewInt(-1)) != 0 {
+				return errors.New("1 != 1 on popInt")
+			}
+			return nil
+		},
+		nil,
+		[][]byte{},
+	},
 	{
 		"popInt -1 leading 0",
 		[][]byte{{0x01,0x00, 0x00, 0x80}},
@@ -253,6 +269,24 @@ var stackTests = []stackTest{
 		nil,
 		[][]byte{},
 	},
+	// Triggers the multibyte case in asInt
+	{
+		"popInt -513",
+		[][]byte{{0x1, 0x82}},
+		func(stack *btcscript.Stack) error {
+			v, err := stack.PopInt()
+			if err != nil {
+				return err
+			}
+			if v.Cmp(big.NewInt(-513)) != 0 {
+				fmt.Printf("%v != %v\n", v, big.NewInt(-513))
+				return errors.New("1 != 1 on popInt")
+			}
+			return nil
+		},
+		nil,
+		[][]byte{},
+	},
 	// Confirm that the asInt code doesn't modify the base data.
 	{
 		"peekint nomodify -1",

test_coverage.txt

@@ -3,8 +3,8 @@ github.com/conformal/btcscript/address.go	 scriptToAddrHashTemplate	 100.00% (45
 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/opcode.go	 parsedOpcode.bytes		 100.00% (23/23)
+github.com/conformal/btcscript/stack.go		 asInt				 100.00% (21/21)
 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/script.go	 signatureScriptCustomReader	 100.00% (15/15)
 github.com/conformal/btcscript/stack.go		 Stack.nipN			 100.00% (14/14)
 github.com/conformal/btcscript/stack.go		 fromInt			 100.00% (14/14)
@@ -147,5 +147,5 @@ 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/script.go	 IsPushOnlyScript		 0.00% (0/4)
 github.com/conformal/btcscript/log.go		 logClosure.String		 0.00% (0/1)
-github.com/conformal/btcscript			 ---------------------------	 96.40% (936/971)
+github.com/conformal/btcscript			 ---------------------------	 96.41% (939/974)