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package codec
// hexMap is a precalculated map of hex nibbles
const hexMap = "" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\xff\xff\xff\xff\xff\xff" +
"\xff\x0a\x0b\x0c\x0d\x0e\x0f\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\x0a\x0b\x0c\x0d\x0e\x0f\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
// likelyHexChars is a set of characters that you would expect to find at
// least one of in hex encoded data. This risks missing some hex data that
// doesn't contain these characters, but gives you the performance gain of not
// trying to decode a lot of long symbols in code.
var likelyHexChars = make([]bool, 256)
func init() {
for _, c := range `0123456789` {
likelyHexChars[c] = true
}
}
// decodeHex decodes hex data
func decodeHex(encodedValue string) string {
size := len(encodedValue)
// hex should have two characters per byte
if size%2 != 0 {
return ""
}
if !hasByte(encodedValue, likelyHexChars) {
return ""
}
decodedValue := make([]byte, size/2)
for i := 0; i < size; i += 2 {
n1 := hexMap[encodedValue[i]]
n2 := hexMap[encodedValue[i+1]]
if n1|n2 == '\xff' {
return ""
}
b := byte(n1<<4 | n2)
if !printableASCII[b] {
return ""
}
decodedValue[i/2] = b
}
return string(decodedValue)
}
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