README
¶
rvarint
Package rvarint implements reverse varint encoding and decoding.
The encoding is similar to varint, but the bytes are written in reverse order.
Usage
This allows you to read varints from the end of a buffer, which can be useful when reading from a buffer that is being filled from the end.
See GoDoc for examples.
The main difference to enconding/binary is that Uvarint and Varint will read from the end of the buffer.
This also means that appending several values will result in the values being read back in reverse order.
Documentation
¶
Overview ¶
Package rvarint implements reverse varint encoding and decoding.
The encoding is similar to varint, but the bytes are written in reverse order.
This means that reading will read from the end of the buffer, and the encoded values will be read in reverse order.
Index ¶
Examples ¶
Constants ¶
const ( MaxVarintLen16 = 3 MaxVarintLen32 = 5 MaxVarintLen64 = 10 )
MaxVarintLenN is the maximum length of a varint-encoded N-bit integer.
Variables ¶
This section is empty.
Functions ¶
func AppendUvarint ¶
AppendUvarint appends the reverse varint-encoded form of x to buf and returns the extended buffer.
Example ¶
package main
import (
"encoding/hex"
"fmt"
"github.com/klauspost/rvarint"
)
func main() {
// Add some existing content to the buffer
buf := []byte("prefix")
// values to encode
values := []uint64{1, 2, 127, 128, 255, 256}
for _, x := range values {
buf = rvarint.AppendUvarint(buf, x)
}
fmt.Printf("encoded: %s\n", hex.EncodeToString(buf))
// When we read back we get the values in *reverse* order.
for range values {
y, n := rvarint.Uvarint(buf)
if n <= 0 {
fmt.Println("unable to read value")
break
}
fmt.Println(y)
buf = buf[:len(buf)-n]
}
fmt.Println("remaining buffer:", string(buf))
}
Output: encoded: 70726566697801027f018001ff0280 256 255 128 127 2 1 remaining buffer: prefix
func AppendVarint ¶
AppendVarint appends the varint-encoded form of x, as generated by PutVarint, to buf and returns the extended buffer.
Example ¶
package main
import (
"encoding/hex"
"fmt"
"github.com/klauspost/rvarint"
)
func main() {
// Add some existing content to the buffer
buf := []byte("prefix")
// values to encode
values := []int64{-65, -64, -2, -1, 0, 1, 2, 63, 64}
for _, x := range values {
buf = rvarint.AppendVarint(buf, x)
}
fmt.Printf("encoded: %s\n", hex.EncodeToString(buf))
// When we read back we get the values in *reverse* order.
for range values {
y, n := rvarint.Varint(buf)
if n <= 0 {
fmt.Println("unable to read value")
break
}
fmt.Println(y)
buf = buf[:len(buf)-n]
}
fmt.Println("remaining buffer:", string(buf))
}
Output: encoded: 70726566697801817f03010002047e0180 64 63 2 1 0 -1 -2 -64 -65 remaining buffer: prefix
func PutUvarint ¶
PutUvarint encodes a uint64 into buf and returns the number of bytes written. If the buffer is too small, PutUvarint will panic.
Example ¶
package main
import (
"fmt"
"github.com/klauspost/rvarint"
)
func main() {
buf := make([]byte, rvarint.MaxVarintLen64)
for _, x := range []uint64{1, 2, 127, 128, 255, 256} {
n := rvarint.PutUvarint(buf, x)
fmt.Printf("%x\n", buf[:n])
}
}
Output: 01 02 7f 0180 01ff 0280
func PutVarint ¶
PutVarint encodes an int64 into buf and returns the number of bytes written. If the buffer is too small, PutVarint will panic.
Example ¶
package main
import (
"fmt"
"github.com/klauspost/rvarint"
)
func main() {
buf := make([]byte, rvarint.MaxVarintLen64)
for _, x := range []int64{-65, -64, -2, -1, 0, 1, 2, 63, 64} {
n := rvarint.PutVarint(buf, x)
fmt.Printf("%x\n", buf[:n])
}
}
Output: 0181 7f 03 01 00 02 04 7e 0180
func Uvarint ¶
Uvarint decodes a uint64 from the end of buf and returns that value and the number of bytes read (> 0). If an error occurred, the value is 0 and the number of bytes n is <= 0 meaning:
n == 0: buf too small
n < 0: value larger than 64 bits (overflow)
and -n is the number of bytes read
On success, the buffer can be truncated using buf = buf[:len(buf)-n]
Example ¶
package main
import (
"fmt"
"github.com/klauspost/rvarint"
)
func main() {
inputs := [][]byte{
{0x01},
{0x02},
{0x7f},
{0x01, 0x80},
{0x01, 0xff},
{0x02, 0x80},
}
for _, b := range inputs {
x, n := rvarint.Uvarint(b)
if n != len(b) {
fmt.Println("Uvarint did not consume all of in")
}
fmt.Println(x)
}
}
Output: 1 2 127 128 255 256
func Varint ¶
Varint decodes an int64 from the end of buf and returns that value and the number of bytes read (> 0). If an error occurred, the value is 0 and the number of bytes n is <= 0 with the following meaning:
n == 0: buf too small
n < 0: value larger than 64 bits (overflow)
and -n is the number of bytes read
On success, the buffer can be truncated using buf = buf[:len(buf)-n]
Example ¶
package main
import (
"fmt"
"github.com/klauspost/rvarint"
)
func main() {
inputs := [][]byte{
{0x01, 0x81},
{0x7f},
{0x03},
{0x01},
{0x00},
{0x02},
{0x04},
{0x7e},
{0x01, 0x80},
}
for _, b := range inputs {
x, n := rvarint.Varint(b)
if n != len(b) {
fmt.Println("Varint did not consume all of in", len(b)-n, "left")
}
fmt.Println(x)
}
}
Output: -65 -64 -2 -1 0 1 2 63 64
Types ¶
This section is empty.
Source Files