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base32.go
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base32.go
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package geohash
// invalid is a placeholder for invalid character decodings.
const invalid = 0xff
// encoding encapsulates an encoding defined by a given base32 alphabet.
type encoding struct {
encode string
decode [256]byte
}
// newEncoding constructs a new encoding defined by the given alphabet,
// which must be a 32-byte string.
func newEncoding(encoder string) *encoding {
e := new(encoding)
e.encode = encoder
for i := 0; i < len(e.decode); i++ {
e.decode[i] = invalid
}
for i := 0; i < len(encoder); i++ {
e.decode[encoder[i]] = byte(i)
}
return e
}
// ValidByte reports whether b is part of the encoding.
func (e *encoding) ValidByte(b byte) bool {
return e.decode[b] != invalid
}
// Decode string into bits of a 64-bit word. The string s may be at most 12
// characters.
func (e *encoding) Decode(s string) uint64 {
x := uint64(0)
for i := 0; i < len(s); i++ {
x = (x << 5) | uint64(e.decode[s[i]])
}
return x
}
// Encode bits of 64-bit word into a string.
func (e *encoding) Encode(x uint64) string {
b := [12]byte{}
for i := 0; i < 12; i++ {
b[11-i] = e.encode[x&0x1f]
x >>= 5
}
return string(b[:])
}
// Base32Encoding with the Geohash alphabet.
var base32encoding = newEncoding("0123456789bcdefghjkmnpqrstuvwxyz")