encoding/binary: PutX functions require buffer of sufficient size.

R=rsc
CC=golang-dev
https://golang.org/cl/5163041

src/pkg/encoding/binary/varint.go

@@ -37,27 +37,15 @@ const (
 )
 
 // PutUvarint encodes a uint64 into buf and returns the number of bytes written.
-// If the buffer is too small, the result is the negated number of bytes required
-// (that is, -PutUvarint(nil, x) is the number of bytes required to encode x).
 func PutUvarint(buf []byte, x uint64) int {
-	var i int
-	for i = range buf {
-		if x < 0x80 {
-			buf[i] = byte(x)
-			return i + 1
-		}
+	i := 0
+	for x >= 0x80 {
 		buf[i] = byte(x) | 0x80
 		x >>= 7
-	}
-	// buffer too small; compute number of bytes required
-	for x >= 0x4000 {
-		x >>= 2 * 7
-		i += 2
-	}
-	if x >= 0x80 {
 		i++
 	}
-	return -(i + 1)
+	buf[i] = byte(x)
+	return i + 1
 }
 
 // Uvarint decodes a uint64 from buf and returns that value and the
@@ -85,8 +73,6 @@ func Uvarint(buf []byte) (uint64, int) {
 }
 
 // PutVarint encodes an int64 into buf and returns the number of bytes written.
-// If the buffer is too small, the result is the negated number of bytes required
-// (that is, -PutVarint(nil, x) is the number of bytes required to encode x).
 func PutVarint(buf []byte, x int64) int {
 	ux := uint64(x) << 1
 	if x < 0 {
@@ -115,7 +101,7 @@ func Varint(buf []byte) (int64, int) {
 // WriteUvarint encodes x and writes the result to w.
 func WriteUvarint(w io.Writer, x uint64) os.Error {
 	var buf [MaxVarintLen64]byte
-	n := PutUvarint(buf[:], x) // won't fail
+	n := PutUvarint(buf[:], x)
 	_, err := w.Write(buf[0:n])
 	return err
 }

src/pkg/encoding/binary/varint_test.go

@@ -11,7 +11,8 @@ import (
 )
 
 func testConstant(t *testing.T, w uint, max int) {
-	n := -PutUvarint(nil, 1<<w-1)
+	var buf [MaxVarintLen64]byte
+	n := PutUvarint(buf[:], 1<<w-1)
 	if n != max {
 		t.Errorf("MaxVarintLen%d = %d; want %d", w, max, n)
 	}
@@ -121,18 +122,6 @@ func TestUvarint(t *testing.T) {
 }
 
 func TestBufferTooSmall(t *testing.T) {
-	for i := 0; i < 10; i++ {
-		buf := make([]byte, i)
-		x := uint64(1) << (uint(i) * 7)
-		n0 := -i
-		if i == 0 {
-			n0 = -1 // encoding 0 takes one byte
-		}
-		if n := PutUvarint(buf, x); n != n0 {
-			t.Errorf("PutUvarint([%d]byte, %d): got n = %d; want %d", len(buf), x, n, n0)
-		}
-	}
-
 	buf := []byte{0x80, 0x80, 0x80, 0x80}
 	for i := 0; i <= len(buf); i++ {
 		buf := buf[0:i]