From 21dc27b115f46bfd340a9731c249f5f7b122413b Mon Sep 17 00:00:00 2001
From: Egon Elbre <egonelbre@gmail.com>
Date: Tue, 24 Nov 2020 14:13:09 +0100
Subject: [PATCH] internal/ops: remove some bounds checks

Currently BCE is unable to understand that the accesses in the code are
safe. Added an explicit slice to make the length bounds obvious.

Signed-off-by: Egon Elbre <egonelbre@gmail.com>
---
 internal/ops/ops.go    | 14 ++++++--------
 internal/ops/reader.go |  2 ++
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/internal/ops/ops.go b/internal/ops/ops.go
index c56b9d6b..da389d9e 100644
--- a/internal/ops/ops.go
+++ b/internal/ops/ops.go
@@ -24,6 +24,7 @@ func (q Quad) Transform(t f32.Affine2D) Quad {
 }
 
 func EncodeQuad(d []byte, q Quad) {
+	d = d[:24]
 	bo := binary.LittleEndian
 	bo.PutUint32(d[0:], math.Float32bits(q.From.X))
 	bo.PutUint32(d[4:], math.Float32bits(q.From.Y))
@@ -34,6 +35,7 @@ func EncodeQuad(d []byte, q Quad) {
 }
 
 func DecodeQuad(d []byte) (q Quad) {
+	d = d[:24]
 	bo := binary.LittleEndian
 	q.From.X = math.Float32frombits(bo.Uint32(d[0:]))
 	q.From.Y = math.Float32frombits(bo.Uint32(d[4:]))
@@ -44,17 +46,13 @@ func DecodeQuad(d []byte) (q Quad) {
 	return
 }
 
-func DecodeTransform(d []byte) (t f32.Affine2D) {
-	if opconst.OpType(d[0]) != opconst.TypeTransform {
+func DecodeTransform(data []byte) (t f32.Affine2D) {
+	if opconst.OpType(data[0]) != opconst.TypeTransform {
 		panic("invalid op")
 	}
-	if len(d) < 1+6*4 {
-		panic("too short buffer")
-	}
-	return decodeAffine2D(d[1:])
-}
+	data = data[1:]
+	data = data[:4*6]
 
-func decodeAffine2D(data []byte) f32.Affine2D {
 	bo := binary.LittleEndian
 	a := math.Float32frombits(bo.Uint32(data))
 	b := math.Float32frombits(bo.Uint32(data[4*1:]))
diff --git a/internal/ops/reader.go b/internal/ops/reader.go
index 5d713db3..0bab3a06 100644
--- a/internal/ops/reader.go
+++ b/internal/ops/reader.go
@@ -143,6 +143,7 @@ func (op *opMacroDef) decode(data []byte) {
 		panic("invalid op")
 	}
 	bo := binary.LittleEndian
+	data = data[:9]
 	dataIdx := int(int32(bo.Uint32(data[1:])))
 	refsIdx := int(int32(bo.Uint32(data[5:])))
 	*op = opMacroDef{
@@ -157,6 +158,7 @@ func (m *macroOp) decode(data []byte, refs []interface{}) {
 	if opconst.OpType(data[0]) != opconst.TypeCall {
 		panic("invalid op")
 	}
+	data = data[:9]
 	bo := binary.LittleEndian
 	dataIdx := int(int32(bo.Uint32(data[1:])))
 	refsIdx := int(int32(bo.Uint32(data[5:])))