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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package hex implements hexadecimal encoding and decoding.
package hex
import (
"os"
"strconv"
)
const hextable = "0123456789abcdef"
// EncodedLen returns the length of an encoding of n source bytes.
func EncodedLen(n int) int { return n * 2 }
// Encode encodes src into EncodedLen(len(src))
// bytes of dst. As a convenience, it returns the number
// of bytes written to dst, but this value is always EncodedLen(len(src)).
// Encode implements hexadecimal encoding.
func Encode(dst, src []byte) int {
for i, v := range src {
dst[i*2] = hextable[v>>4]
dst[i*2+1] = hextable[v&0x0f]
}
return len(src) * 2
}
// OddLengthInputError results from decoding an odd length slice.
type OddLengthInputError struct{}
func (OddLengthInputError) String() string { return "odd length hex string" }
// InvalidHexCharError results from finding an invalid character in a hex string.
type InvalidHexCharError byte
func (e InvalidHexCharError) String() string {
return "invalid hex char: " + strconv.Itoa(int(e))
}
func DecodedLen(x int) int { return x / 2 }
// Decode decodes src into DecodedLen(len(src)) bytes, returning the actual
// number of bytes written to dst.
//
// If Decode encounters invalid input, it returns an OddLengthInputError or an
// InvalidHexCharError.
func Decode(dst, src []byte) (int, os.Error) {
if len(src)%2 == 1 {
return 0, OddLengthInputError{}
}
for i := 0; i < len(src)/2; i++ {
a, ok := fromHexChar(src[i*2])
if !ok {
return 0, InvalidHexCharError(src[i*2])
}
b, ok := fromHexChar(src[i*2+1])
if !ok {
return 0, InvalidHexCharError(src[i*2+1])
}
dst[i] = (a << 4) | b
}
return len(src) / 2, nil
}
// fromHexChar converts a hex character into its value and a success flag.
func fromHexChar(c byte) (byte, bool) {
switch {
case '0' <= c && c <= '9':
return c - '0', true
case 'a' <= c && c <= 'f':
return c - 'a' + 10, true
case 'A' <= c && c <= 'F':
return c - 'A' + 10, true
}
return 0, false
}
// EncodeToString returns the hexadecimal encoding of src.
func EncodeToString(src []byte) string {
dst := make([]byte, EncodedLen(len(src)))
Encode(dst, src)
return string(dst)
}
// DecodeString returns the bytes represented by the hexadecimal string s.
func DecodeString(s string) ([]byte, os.Error) {
src := []byte(s)
dst := make([]byte, DecodedLen(len(src)))
_, err := Decode(dst, src)
if err != nil {
return nil, err
}
return dst, nil
}
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