[PHP] Geo Hash encode and decode function.

geohash.php

<?php

function geohash($lat, $lon = NULL, $len = 12)
{
	if ($len < 1 || $len > 12) {
		return false;
	}

	$base32Chars = array(
		'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'b', 'c', 'd', 'e', 'f', 'g',
		'h', 'j', 'k', 'm', 'n', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
	);

	$latInterval  = array(-90.0, 90.0);
	$lonInterval = array(-180.0, 180.0);
	$bits = array(16, 8, 4, 2, 1);
	$bit = 0;
	$isEven = TRUE;

	// Encode
	if (!empty($lon) && preg_match('/\A[\d\.]+\z/', $lat.$lon)) {
		$charIndex = 0;
		$geohash = NULL;

		while (strlen($geohash) < $len) {
			if ($isEven) {
				$middle = ($lonInterval[0] + $lonInterval[1]) / 2;
				if ($lon > $middle) {
					$charIndex |= $bits[$bit];
					$lonInterval[0] = $middle;
				} else {
					$lonInterval[1] = $middle;
				}
			} else {
				$middle = ($latInterval[0] + $latInterval[1]) / 2;
				if ($lat > $middle) {
					$charIndex |= $bits[$bit];
					$latInterval[0] = $middle;
				} else {
					$latInterval[1] = $middle;
				}
			}

			if ($bit < 4) {
				$bit++;
			} else {
				$geohash .= $base32Chars[$charIndex];
				$bit           = 0;
				$charIndex     = 0;
			}

			$isEven = $isEven ? FALSE : TRUE;
		}

		return $geohash;
	}

	// Decode
	elseif(empty($lon) && is_string($lat) && ($geohashLength = strlen($lat)) <= 12) {
		$geohash = $lat;
		$base32DecodeMap  = array_flip($base32Chars);

		for ($i = 0; $i < $geohashLength; $i++) {
			if (!isset($base32DecodeMap[$geohash[$i]])) {
				// Invalid GeoHash
				return FALSE;
			}

			$currentChar = $base32DecodeMap[$geohash[$i]];
			$bitsTotal = count($bits);
			for ($j = 0; $j < $bitsTotal; $j++) {
				$mask = $bits[$j];

				if ($isEven) {
					if (($currentChar & $mask) !== 0) {
						$lonInterval[0] = ($lonInterval[0] + $lonInterval[1]) / 2;
					} else {
						$lonInterval[1] = ($lonInterval[0] + $lonInterval[1]) / 2;
					}
				} else {
					if (($currentChar & $mask) !== 0) {
						$latInterval[0] = ($latInterval[0] + $latInterval[1]) / 2;
					} else {
						$latInterval[1] = ($latInterval[0] + $latInterval[1]) / 2;
					}
				}
				
				$isEven = $isEven ? FALSE : TRUE;
			}
		}

		return array(
			'lat' => ($latInterval[0] + $latInterval[1]) / 2,
			'lon' => ($lonInterval[0] + $lonInterval[1]) / 2
		);
	}
}