mirror of https://github.com/tidwall/tile38.git
45 lines
1.0 KiB
Go
45 lines
1.0 KiB
Go
package geohash
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// encoding encapsulates an encoding defined by a given base32 alphabet.
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type encoding struct {
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encode string
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decode [256]byte
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}
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// newEncoding constructs a new encoding defined by the given alphabet,
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// which must be a 32-byte string.
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func newEncoding(encoder string) *encoding {
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e := new(encoding)
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e.encode = encoder
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for i := 0; i < len(e.decode); i++ {
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e.decode[i] = 0xff
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}
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for i := 0; i < len(encoder); i++ {
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e.decode[encoder[i]] = byte(i)
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}
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return e
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}
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// Decode string into bits of a 64-bit word. The string s may be at most 12
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// characters.
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func (e *encoding) Decode(s string) uint64 {
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x := uint64(0)
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for i := 0; i < len(s); i++ {
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x = (x << 5) | uint64(e.decode[s[i]])
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}
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return x
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}
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// Encode bits of 64-bit word into a string.
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func (e *encoding) Encode(x uint64) string {
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b := [12]byte{}
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for i := 0; i < 12; i++ {
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b[11-i] = e.encode[x&0x1f]
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x >>= 5
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}
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return string(b[:])
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}
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// Base32Encoding with the Geohash alphabet.
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var base32encoding = newEncoding("0123456789bcdefghjkmnpqrstuvwxyz")
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