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encoding/binary: add AppendVarint AppendUvarint

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This adds a straight-forward implementation of the functionality.
A more performant version could be added that unrolls the loop
as is done in google.golang.org/protobuf/encoding/protowire,
but usages that demand high performance can use that package instead.

Fixes #51644

Change-Id: I9d3b615a60cdff47e5200e7e5d2276adf4c93783
Reviewed-on: https://go-review.googlesource.com/c/go/+/400176
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Joe Tsai 2022-04-13 13:21:30 -07:00 committed by Joseph Tsai
parent 5a4f0b6f1e
commit 35a92f92bd
3 changed files with 34 additions and 0 deletions
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2
api/next/51644.txt Normal file
View File

@ -0,0 +1,2 @@
pkg encoding/binary, func AppendUvarint([]uint8, uint64) []uint8 #51644
pkg encoding/binary, func AppendVarint([]uint8, int64) []uint8 #51644

20
src/encoding/binary/varint.go
View File

@ -36,6 +36,16 @@ const (
MaxVarintLen64 = 10
)
// AppendUvarint appends the varint-encoded form of x,
// as generated by PutUvarint, to buf and returns the extended buffer.
func AppendUvarint(buf []byte, x uint64) []byte {
for x >= 0x80 {
buf = append(buf, byte(x)|0x80)
x >>= 7
}
return append(buf, byte(x))
}
// PutUvarint encodes a uint64 into buf and returns the number of bytes written.
// If the buffer is too small, PutUvarint will panic.
func PutUvarint(buf []byte, x uint64) int {
@ -77,6 +87,16 @@ func Uvarint(buf []byte) (uint64, int) {
return 0, 0
}
// AppendVarint appends the varint-encoded form of x,
// as generated by PutVarint, to buf and returns the extended buffer.
func AppendVarint(buf []byte, x int64) []byte {
ux := uint64(x) << 1
if x < 0 {
ux = ^ux
}
return AppendUvarint(buf, ux)
}
// PutVarint encodes an int64 into buf and returns the number of bytes written.
// If the buffer is too small, PutVarint will panic.
func PutVarint(buf []byte, x int64) int {

12
src/encoding/binary/varint_test.go
View File

@ -36,6 +36,12 @@ func testVarint(t *testing.T, x int64) {
t.Errorf("Varint(%d): got n = %d; want %d", x, m, n)
}
buf2 := []byte("prefix")
buf2 = AppendVarint(buf2, x)
if string(buf2) != "prefix"+string(buf[:n]) {
t.Errorf("AppendVarint(%d): got %q, want %q", x, buf2, "prefix"+string(buf[:n]))
}
y, err := ReadVarint(bytes.NewReader(buf))
if err != nil {
t.Errorf("ReadVarint(%d): %s", x, err)
@ -56,6 +62,12 @@ func testUvarint(t *testing.T, x uint64) {
t.Errorf("Uvarint(%d): got n = %d; want %d", x, m, n)
}
buf2 := []byte("prefix")
buf2 = AppendUvarint(buf2, x)
if string(buf2) != "prefix"+string(buf[:n]) {
t.Errorf("AppendUvarint(%d): got %q, want %q", x, buf2, "prefix"+string(buf[:n]))
}
y, err := ReadUvarint(bytes.NewReader(buf))
if err != nil {
t.Errorf("ReadUvarint(%d): %s", x, err)