From ebd9f1bd4c39bc2fe3bcf6f0d3c81f70dae495d8 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Alexandru=20Mo=C8=99oi?= <mosoi@google.com>
Date: Sun, 13 Mar 2016 22:12:03 +0100
Subject: [PATCH] encoding/binary: remove bound checks from conversions.
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* This the simplest solution I could came up with
that doesn't required changing the compiler.
* The bound checks become constants now
so they are removed during opt phase.

Updates #14808

Change-Id: If32c33d7ec08bb400321b465015d152f0a5d3001
Reviewed-on: https://go-review.googlesource.com/20654
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>
---
 src/encoding/binary/binary.go | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/encoding/binary/binary.go b/src/encoding/binary/binary.go
index d2e267eca5..69b7b03091 100644
--- a/src/encoding/binary/binary.go
+++ b/src/encoding/binary/binary.go
@@ -48,18 +48,24 @@ var BigEndian bigEndian
 
 type littleEndian struct{}
 
-func (littleEndian) Uint16(b []byte) uint16 { return uint16(b[0]) | uint16(b[1])<<8 }
+func (littleEndian) Uint16(b []byte) uint16 {
+	b = b[:2] // bounds check hint to compiler; see golang.org/issue/14808
+	return uint16(b[0]) | uint16(b[1])<<8
+}
 
 func (littleEndian) PutUint16(b []byte, v uint16) {
+	b = b[:2] // early bounds check to guarantee safety of writes below
 	b[0] = byte(v)
 	b[1] = byte(v >> 8)
 }
 
 func (littleEndian) Uint32(b []byte) uint32 {
+	b = b[:4] // bounds check hint to compiler; see golang.org/issue/14808
 	return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
 }
 
 func (littleEndian) PutUint32(b []byte, v uint32) {
+	b = b[:4] // early bounds check to guarantee safety of writes below
 	b[0] = byte(v)
 	b[1] = byte(v >> 8)
 	b[2] = byte(v >> 16)
@@ -67,11 +73,13 @@ func (littleEndian) PutUint32(b []byte, v uint32) {
 }
 
 func (littleEndian) Uint64(b []byte) uint64 {
+	b = b[:8] // bounds check hint to compiler; see golang.org/issue/14808
 	return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
 		uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
 }
 
 func (littleEndian) PutUint64(b []byte, v uint64) {
+	b = b[:8] // early bounds check to guarantee safety of writes below
 	b[0] = byte(v)
 	b[1] = byte(v >> 8)
 	b[2] = byte(v >> 16)
@@ -88,18 +96,24 @@ func (littleEndian) GoString() string { return "binary.LittleEndian" }
 
 type bigEndian struct{}
 
-func (bigEndian) Uint16(b []byte) uint16 { return uint16(b[1]) | uint16(b[0])<<8 }
+func (bigEndian) Uint16(b []byte) uint16 {
+	b = b[:2] // bounds check hint to compiler; see golang.org/issue/14808
+	return uint16(b[1]) | uint16(b[0])<<8
+}
 
 func (bigEndian) PutUint16(b []byte, v uint16) {
+	b = b[:2] // early bounds check to guarantee safety of writes below
 	b[0] = byte(v >> 8)
 	b[1] = byte(v)
 }
 
 func (bigEndian) Uint32(b []byte) uint32 {
+	b = b[:4] // bounds check hint to compiler; see golang.org/issue/14808
 	return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
 }
 
 func (bigEndian) PutUint32(b []byte, v uint32) {
+	b = b[:4] // early bounds check to guarantee safety of writes below
 	b[0] = byte(v >> 24)
 	b[1] = byte(v >> 16)
 	b[2] = byte(v >> 8)
@@ -107,11 +121,13 @@ func (bigEndian) PutUint32(b []byte, v uint32) {
 }
 
 func (bigEndian) Uint64(b []byte) uint64 {
+	b = b[:8] // bounds check hint to compiler; see golang.org/issue/14808
 	return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
 		uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
 }
 
 func (bigEndian) PutUint64(b []byte, v uint64) {
+	b = b[:8] // early bounds check to guarantee safety of writes below
 	b[0] = byte(v >> 56)
 	b[1] = byte(v >> 48)
 	b[2] = byte(v >> 40)
-- 
2.50.0