freetype/truetype: jump opcodes.

R=gri, bsiegert
CC=golang-dev
http://codereview.appspot.com/6344079

freetype/truetype/hint.go

@@ -25,7 +25,7 @@ func (h *hinter) run(program []byte) error {
 		steps, pc, top int
 		opcode         uint8
 	)
-	for int(pc) < len(program) {
+	for 0 <= pc && int(pc) < len(program) {
 		steps++
 		if steps == 100000 {
 			return errors.New("truetype: hinting: too many steps")
@@ -43,6 +43,11 @@ func (h *hinter) run(program []byte) error {
 			opcode = 1
 			goto ifelse
 
+		case opJMPR:
+			top--
+			pc += int(h.stack[top])
+			continue
+
 		case opDUP:
 			if int(top) >= len(h.stack) {
 				return errors.New("truetype: hinting: stack overflow")
@@ -89,36 +94,36 @@ func (h *hinter) run(program []byte) error {
 			// No-op.
 
 		case opLT:
-			h.stack[top-2] = bool2int32(h.stack[top-2] < h.stack[top-1])
 			top--
+			h.stack[top-1] = bool2int32(h.stack[top-1] < h.stack[top])
 
 		case opLTEQ:
-			h.stack[top-2] = bool2int32(h.stack[top-2] <= h.stack[top-1])
 			top--
+			h.stack[top-1] = bool2int32(h.stack[top-1] <= h.stack[top])
 
 		case opGT:
-			h.stack[top-2] = bool2int32(h.stack[top-2] > h.stack[top-1])
 			top--
+			h.stack[top-1] = bool2int32(h.stack[top-1] > h.stack[top])
 
 		case opGTEQ:
-			h.stack[top-2] = bool2int32(h.stack[top-2] >= h.stack[top-1])
 			top--
+			h.stack[top-1] = bool2int32(h.stack[top-1] >= h.stack[top])
 
 		case opEQ:
-			h.stack[top-2] = bool2int32(h.stack[top-2] == h.stack[top-1])
 			top--
+			h.stack[top-1] = bool2int32(h.stack[top-1] == h.stack[top])
 
 		case opNEQ:
-			h.stack[top-2] = bool2int32(h.stack[top-2] != h.stack[top-1])
 			top--
+			h.stack[top-1] = bool2int32(h.stack[top-1] != h.stack[top])
 
 		case opAND:
-			h.stack[top-2] = bool2int32(h.stack[top-2] != 0 && h.stack[top-1] != 0)
 			top--
+			h.stack[top-1] = bool2int32(h.stack[top-1] != 0 && h.stack[top] != 0)
 
 		case opOR:
-			h.stack[top-2] = bool2int32(h.stack[top-2]|h.stack[top-1] != 0)
 			top--
+			h.stack[top-1] = bool2int32(h.stack[top-1]|h.stack[top] != 0)
 
 		case opNOT:
 			h.stack[top-1] = bool2int32(h.stack[top-1] == 0)
@@ -134,23 +139,23 @@ func (h *hinter) run(program []byte) error {
 			// No-op.
 
 		case opADD:
-			h.stack[top-2] += h.stack[top-1]
 			top--
+			h.stack[top-1] += h.stack[top]
 
 		case opSUB:
-			h.stack[top-2] -= h.stack[top-1]
 			top--
+			h.stack[top-1] -= h.stack[top]
 
 		case opDIV:
-			if h.stack[top-1] == 0 {
+			top--
+			if h.stack[top] == 0 {
 				return errors.New("truetype: hinting: division by zero")
 			}
-			h.stack[top-2] = int32((int64(h.stack[top-2]) << 6) / int64(h.stack[top-1]))
-			top--
+			h.stack[top-1] = int32((int64(h.stack[top-1]) << 6) / int64(h.stack[top]))
 
 		case opMUL:
-			h.stack[top-2] = int32((int64(h.stack[top-2]) * int64(h.stack[top-1])) >> 6)
 			top--
+			h.stack[top-1] = int32((int64(h.stack[top-1]) * int64(h.stack[top])) >> 6)
 
 		case opABS:
 			if h.stack[top-1] < 0 {
@@ -167,6 +172,20 @@ func (h *hinter) run(program []byte) error {
 			h.stack[top-1] += 63
 			h.stack[top-1] &^= 63
 
+		case opJROT:
+			top -= 2
+			if h.stack[top+1] != 0 {
+				pc += int(h.stack[top])
+				continue
+			}
+
+		case opJROF:
+			top -= 2
+			if h.stack[top+1] == 0 {
+				pc += int(h.stack[top])
+				continue
+			}
+
 		case opPUSHB000, opPUSHB001, opPUSHB010, opPUSHB011, opPUSHB100, opPUSHB101, opPUSHB110, opPUSHB111:
 			opcode -= opPUSHB000 - 1
 			goto push

freetype/truetype/hint_test.go

@@ -26,6 +26,18 @@ func TestBytecode(t *testing.T) {
 			nil,
 			"underflow",
 		},
+		{
+			"infinite loop",
+			[]byte{
+				opPUSHW000, // [-1]
+				0xff,
+				0xff,
+				opDUP,  // [-1, -1]
+				opJMPR, // [-1]
+			},
+			nil,
+			"too many steps",
+		},
 		{
 			"unbalanced if/else",
 			[]byte{
@@ -36,6 +48,33 @@ func TestBytecode(t *testing.T) {
 			nil,
 			"unbalanced",
 		},
+		{
+			"jumps",
+			[]byte{
+				opPUSHB001, // [10, 2]
+				10,
+				2,
+				opJMPR,     // [10]
+				opDUP,      // not executed
+				opDUP,      // [10, 10]
+				opPUSHB010, // [10, 10, 20, 2, 1]
+				20,
+				2,
+				1,
+				opJROT,     // [10, 10, 20]
+				opDUP,      // not executed
+				opDUP,      // [10, 10, 20, 20]
+				opPUSHB010, // [10, 10, 20, 20, 30, 2, 1]
+				30,
+				2,
+				1,
+				opJROF, // [10, 10, 20, 20, 30]
+				opDUP,  // [10, 10, 20, 20, 30, 30]
+				opDUP,  // [10, 10, 20, 20, 30, 30, 30]
+			},
+			[]int32{10, 10, 20, 20, 30, 30, 30},
+			"",
+		},
 		{
 			"stack ops",
 			[]byte{

freetype/truetype/opcodes.go

@@ -38,7 +38,7 @@ const (
 	opRTHG      = 0x19
 	opSMD       = 0x1a
 	opELSE      = 0x1b // ELSE clause
-	opJMPR      = 0x1c
+	opJMPR      = 0x1c // JuMP Relative
 	opSCVTCI    = 0x1d
 	opSSWCI     = 0x1e
 	opSSW       = 0x1f
@@ -130,8 +130,8 @@ const (
 	opDELTAC3   = 0x75
 	opSROUND    = 0x76
 	opS45ROUND  = 0x77
-	opJROT      = 0x78
-	opJROF      = 0x79
+	opJROT      = 0x78 // Jump Relative On True
+	opJROF      = 0x79 // Jump Relative On False
 	opROFF      = 0x7a
 	op_0x7b     = 0x7b
 	opRUTG      = 0x7c
@@ -272,13 +272,13 @@ const (
 var popCount = [256]uint8{
 	// 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f
 	q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, // 0x00 - 0x0f
-	q, q, q, q, q, q, q, q, q, q, q, 0, q, q, q, q, // 0x10 - 0x1f
+	q, q, q, q, q, q, q, q, q, q, q, 0, 1, q, q, q, // 0x10 - 0x1f
 	1, 1, 0, 2, 0, 1, 1, q, q, q, q, q, q, q, q, q, // 0x20 - 0x2f
 	q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, // 0x30 - 0x3f
 	0, 0, q, q, q, q, q, q, q, q, q, q, q, q, q, 0, // 0x40 - 0x4f
 	2, 2, 2, 2, 2, 2, q, q, 1, 0, 2, 2, 1, q, q, q, // 0x50 - 0x5f
 	2, 2, 2, 2, 1, 1, 1, 1, q, q, q, q, q, q, q, q, // 0x60 - 0x6f
-	q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, // 0x70 - 0x7f
+	q, q, q, q, q, q, q, q, 2, 2, q, q, q, q, q, q, // 0x70 - 0x7f
 	q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, // 0x80 - 0x8f
 	q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, // 0x90 - 0x9f
 	q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, // 0xa0 - 0xaf