geohash into 32 bits

geohash2bits.go

package main

import (
	"fmt"
)

func main() {
	geohash := "u4pruydqqvj"
	for i := range geohash {
		fmt.Println(geohash[:i+1], "\t", geohash2bits(geohash[:i+1]))
	}
}



func geohash2bits(s string) int64 {
	ret := int64(0)
	byt := []byte(s)
	// a single base32 character is 5 bits
	// and our destination is the 63 least significant bits of an int64
	// so, we can fit 12 3/5 characters in the int
	for i := 0; i < len(byt) && i < 12; i++ {
		ret = (base32[byt[i]] << (i*5)) | ret
	}

	return ret
}

var base32 = [256]int64{
	'0': 0,
	'1': 1,
	'2': 2,
	'3': 3,
	'4': 4,
	'5': 5,
	'6': 6,
	'7': 7,
	'8': 8,
	'9': 9,
	'b': 10,
	'c': 11,
	'd': 12,
	'e': 13,
	'f': 14,
	'g': 15,
	'h': 16,
	'j': 17,
	'k': 18,
	'm': 19,
	'n': 20,
	'p': 21,
	'q': 22,
	'r': 23,
	's': 24,
	't': 25,
	'u': 26,
	'v': 27,
	'w': 28,
	'x': 29,
	'y': 30,
	'z': 31,
}

geohash2bits.sql

CREATE OR REPLACE FUNCTION base32_decode(IN hash text) RETURNS bigint AS $$
DECLARE
	tbl bigint[] := ARRAY[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 10, 11, 12, 13, 14, 15, 16, 0, 17, 18, 0, 19, 20, 0,
						   21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
						   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
	ret bigint := 0;
	it integer := 0;
BEGIN
	-- a single base32 character is 5 bits
	-- and our destination is the 63 least significant bits of and int64
	--
	-- so we can fit 12 3/5 characters in our destination. To prevent overflow
	-- into the sign bit, we use 12 characters
	WHILE it < LENGTH(hash) AND it < 12 LOOP
		ret := (tbl[1+ASCII(SUBSTRING(hash, it+1, 1))] << (it * 5)) | ret;
		it := it+1;
	END LOOP;
	RETURN ret;
END;
$$ LANGUAGE plpgsql IMMUTABLE;