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Merge pull request #4 from Vectorial1024/olc_x86_x64
Use "long" int calculators where possible
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‎README.md‎

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composer require vectorial1024/open-location-code-php
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```
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**Special Notice**: to ensure 32-bit PHP compatibility, this library uses `float` variables instead of `int` variables to calculate Open Location Codes.
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This may cause inaccuracies in some unforseen edge cases, but generally speaking, there should be no problems.
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**Special Notice**: to ensure 32-bit PHP compatibility, this library will check the PHP runtime and, if it detects a 32-bit PHP runtime, will use `float` variables instead of `int` variables to calculate Open Location Codes.
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This may cause some unintended inaccuracies in 32-bit PHP, but generally speaking, there should be no problems.
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## Example code
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‎src/CodeCalculator/AbstractCodeCalculator.php‎

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<?php
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namespace Vectorial1024\OpenLocationCodePhp\CodeCalculator;
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use Vectorial1024\OpenLocationCodePhp\CodeArea;
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use Vectorial1024\OpenLocationCodePhp\OpenLocationCode;
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/**
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* An abstract class to provide a unified API for the 32-bit and 64-bit Open Location Code calculators.
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*/
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abstract class AbstractCodeCalculator
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{
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// Value to multiple latitude degrees to convert it to an integer with the maximum encoding
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// precision. I.e. ENCODING_BASE**3 * GRID_ROWS**GRID_CODE_LENGTH
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protected const int LAT_INTEGER_MULTIPLIER = 8000 * 3125;
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// Value to multiple longitude degrees to convert it to an integer with the maximum encoding
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// precision. I.e. ENCODING_BASE**3 * GRID_COLUMNS**GRID_CODE_LENGTH
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protected const int LNG_INTEGER_MULTIPLIER = 8000 * 1024;
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/**
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* Assuming the given latitude and longitude are valid, encode these coordinates into an Open Location Code.
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* @param float $latitude The latitude in decimal degrees.
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* @param float $longitude The longitude in decimal degrees.
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* @param int $codeLength The desired number of digits in the code.
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* @return string The resulting (string) Open Location Code.
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*/
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public function encode(float $latitude, float $longitude, int $codeLength): string
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{
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// Let the calculator correctly generate the reversed code
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$revCode = static::generateRevOlcCode($latitude, $longitude, $codeLength);
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// Reverse the code
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$code = strrev($revCode);
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// If we need to pad the code, replace some of the digits.
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if ($codeLength < OpenLocationCode::SEPARATOR_POSITION) {
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for ($i = $codeLength; $i < OpenLocationCode::SEPARATOR_POSITION; $i++) {
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$code[$i] = OpenLocationCode::PADDING_CHARACTER;
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}
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}
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$finalCode = substr($code, 0, max(OpenLocationCode::SEPARATOR_POSITION + 1, $codeLength + 1));
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return $finalCode;
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}
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/**
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* Performs the necessary calculation to generate a reversed (and possibly incomplete) Open Location Code from the given coordinates.
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* The exact implementation depends on whether the 32-bit/64-bit calculator is used, but the idea should be the same.
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* @param float $latitude The latitude in decimal degrees.
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* @param float $longitude The longitude in decimal degrees.
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* @param int $codeLength The desired number of digits in the code.
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* @return string The resulting (string) Open Location Code.
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*/
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abstract protected function generateRevOlcCode(float $latitude, float $longitude, int $codeLength): string;
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/**
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* Assuming the given Open Location Code is valid, decodes it into a CodeArea object encapsulating latitude/longitude bounding box.
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* @param string $code The stripped Open Location Code.
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* @return CodeArea A CodeArea object.
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*/
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public function decode(string $code): CodeArea
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{
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// Strip padding and separator characters out of the code.
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$clean = str_replace([OpenLocationCode::SEPARATOR, OpenLocationCode::PADDING_CHARACTER], "", $code);
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return $this->generateCodeArea($clean);
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}
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/**
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* Performs the necessary calculation to generate a CodeArea object from the given (stripped) Open Location Code.
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* @param string $strippedCode The stripped Open Location Code.
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* @return CodeArea A CodeArea object.
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*/
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abstract protected function generateCodeArea(string $strippedCode): CodeArea;
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/**
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* Returns a static instance of the appropriate code calculator depending on whether the current PHP is 32-bit/64-bit.
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* 32-bit PHP will get a calculator that uses floats, while 64-bit PHP will get a calculator that uses "long" ints.
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*
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* This is required to allow 32-bit PHP environments to correctly calculate Open Location Codes, while preserving
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* the performance advantage of 64-bit PHP by using integer operations.
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* @return CodeCalculatorFloat|CodeCalculatorInt The appropriate code calculator.
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*/
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public static function getDefaultCalculator(): CodeCalculatorFloat|CodeCalculatorInt
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{
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// check PHP environment to give int calculator where possible
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// 32-bit PHP has 32-bit int, which uses 4 bytes i.e. PHP_INT_SIZE = 4
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// initializing static variables with constructors is only allowed for PHP 8.3+
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static $defaultCalculator = PHP_INT_SIZE > 4 ? new CodeCalculatorInt() : new CodeCalculatorFloat();
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return $defaultCalculator;
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}
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}

‎src/CodeCalculator/CodeCalculatorFloat.php‎

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<?php
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namespace Vectorial1024\OpenLocationCodePhp\CodeCalculator;
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use Vectorial1024\OpenLocationCodePhp\CodeArea;
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use Vectorial1024\OpenLocationCodePhp\OpenLocationCode;
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/**
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* A Open Location Code calculator that uses float.
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* As such, this is usable on any PHP version. but may have unforeseen inaccuracy.
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*/
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class CodeCalculatorFloat extends AbstractCodeCalculator
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{
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// Value of the most significant latitude digit after it has been converted to an integer.
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// Note: to ensure 32bit PHP compatibility, this is now a precisely-represented float.
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public const float LAT_MSP_VALUE = self::LAT_INTEGER_MULTIPLIER * OpenLocationCode::ENCODING_BASE * OpenLocationCode::ENCODING_BASE;
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// Value of the most significant longitude digit after it has been converted to an integer.
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// Note: to ensure 32bit PHP compatibility, this is now a precisely-represented float.
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public const float LNG_MSP_VALUE = self::LNG_INTEGER_MULTIPLIER * OpenLocationCode::ENCODING_BASE * OpenLocationCode::ENCODING_BASE;
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protected function generateRevOlcCode(float $latitude, float $longitude, int $codeLength): string
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{
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// PHP has native support for string concatenation, and string reversal is quite fast.
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$revCode = "";
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// Compute the code.
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// The idea of this approach is to convert each value to an integer
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// after multiplying it by the final precision.
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// This allows us to use only integer operations, so
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// avoiding any accumulation of floating point representation errors.
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// However, it must also be noted that the calculation may poduce 10-digit integers
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// that begins with 6, which overflows the 32-bit PHP int type.
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// The good news is, this relatively small bignum can be precisely represented
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// by the double-precision float type. We just need to be careful when calculating.
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// Multiply values by their precision and convert to positive.
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// Rounding avoids/minimizes errors due to floating-point precision.
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// Since the numbers are positive, floor() is equivalent to intval().
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$latVal = floor(round(($latitude + OpenLocationCode::LATITUDE_MAX) * self::LAT_INTEGER_MULTIPLIER * 1e6) / 1e6);
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$lngVal = floor(round(($longitude + OpenLocationCode::LONGITUDE_MAX) * self::LNG_INTEGER_MULTIPLIER * 1e6) / 1e6);
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// Compute the grid part of the code if necessary.
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if ($codeLength > OpenLocationCode::PAIR_CODE_LENGTH) {
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for ($i = 0; $i < OpenLocationCode::GRID_CODE_LENGTH; $i++) {
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$latDigit = (int) fmod($latVal, OpenLocationCode::GRID_ROWS);
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$lngDigit = (int) fmod($lngVal, OpenLocationCode::GRID_COLUMNS);
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$ndx = $latDigit * OpenLocationCode::GRID_COLUMNS + $lngDigit;
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$revCode .= OpenLocationCode::CODE_ALPHABET[$ndx];
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$latVal = floor($latVal / OpenLocationCode::GRID_ROWS);
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$lngVal = floor($lngVal / OpenLocationCode::GRID_COLUMNS);
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}
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unset($i, $latDigit, $lngDigit, $ndx);
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} else {
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$latVal = floor($latVal / pow(OpenLocationCode::GRID_ROWS, OpenLocationCode::GRID_CODE_LENGTH));
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$lngVal = floor($lngVal / pow(OpenLocationCode::GRID_COLUMNS, OpenLocationCode::GRID_CODE_LENGTH));
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}
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// Compute the pair section of the code.
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for ($i = 0; $i < intdiv(OpenLocationCode::PAIR_CODE_LENGTH, 2); $i++) {
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$revCode .= OpenLocationCode::CODE_ALPHABET[(int) fmod($lngVal, OpenLocationCode::ENCODING_BASE)];
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$revCode .= OpenLocationCode::CODE_ALPHABET[(int) fmod($latVal, OpenLocationCode::ENCODING_BASE)];
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$latVal = floor($latVal / OpenLocationCode::ENCODING_BASE);
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$lngVal = floor($lngVal / OpenLocationCode::ENCODING_BASE);
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// If we are at the separator position, add the separator
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if ($i == 0) {
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$revCode .= OpenLocationCode::SEPARATOR;
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}
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}
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return $revCode;
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}
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protected function generateCodeArea(string $strippedCode): CodeArea
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{
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// Initialize the values.
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// We will assume these values are floats to ensure 32bit PHP compatibility.
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// See relevant comments in encode() above.
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$latVal = -OpenLocationCode::LATITUDE_MAX * self::LAT_INTEGER_MULTIPLIER;
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$lngVal = -OpenLocationCode::LONGITUDE_MAX * self::LNG_INTEGER_MULTIPLIER;
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// Define the place value for the digits. We'll divide this down as we work through the code.
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$latPlaceVal = self::LAT_MSP_VALUE;
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$lngPlaceVal = self::LNG_MSP_VALUE;
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for ($i = OpenLocationCode::PAIR_CODE_LENGTH; $i < min(strlen($strippedCode), OpenLocationCode::MAX_DIGIT_COUNT); $i += 2) {
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$latPlaceVal = floor($latPlaceVal / OpenLocationCode::ENCODING_BASE);
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$lngPlaceVal = floor($lngPlaceVal / OpenLocationCode::ENCODING_BASE);
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$latVal += strpos(OpenLocationCode::CODE_ALPHABET, $strippedCode[$i]) * $latPlaceVal;
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$lngVal += strpos(OpenLocationCode::CODE_ALPHABET, $strippedCode[$i + 1]) * $lngPlaceVal;
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}
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unset($i);
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for ($i = OpenLocationCode::PAIR_CODE_LENGTH; $i < min(strlen($strippedCode), OpenLocationCode::MAX_DIGIT_COUNT); $i++) {
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$latPlaceVal = floor($latPlaceVal / OpenLocationCode::GRID_ROWS);
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$lngPlaceVal = floor($lngPlaceVal / OpenLocationCode::GRID_COLUMNS);
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$digit = strpos(OpenLocationCode::CODE_ALPHABET, $strippedCode[$i]);
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$row = intdiv($digit, OpenLocationCode::GRID_COLUMNS);
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$col = $digit % OpenLocationCode::GRID_COLUMNS;
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$latVal += $row * $latPlaceVal;
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$lngVal += $col * $lngPlaceVal;
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unset($digit);
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}
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unset($i);
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$latitudeLo = $latVal / self::LAT_INTEGER_MULTIPLIER;
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$longitudeLo = $lngVal / self::LNG_INTEGER_MULTIPLIER;
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$latitudeHi = ($latVal + $latPlaceVal) / self::LAT_INTEGER_MULTIPLIER;
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$longitudeHi = ($lngVal + $lngPlaceVal) / self::LNG_INTEGER_MULTIPLIER;
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return new CodeArea(
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$latitudeLo,
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$longitudeLo,
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$latitudeHi,
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$longitudeHi,
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min(strlen($strippedCode), OpenLocationCode::MAX_DIGIT_COUNT),
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);
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}
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}

‎src/CodeCalculator/CodeCalculatorInt.php‎

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<?php
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namespace Vectorial1024\OpenLocationCodePhp\CodeCalculator;
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use RuntimeException;
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use Vectorial1024\OpenLocationCodePhp\CodeArea;
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use Vectorial1024\OpenLocationCodePhp\OpenLocationCode;
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/**
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* A Open Location Code calculator that uses "long" int.
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* As such, this has ensured accuracy, but cannot be used in 32-bit PHP.
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*/
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class CodeCalculatorInt extends AbstractCodeCalculator
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{
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// Value of the most significant latitude digit after it has been converted to an integer.
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// Note: since we are using 64-bit PHP, this can be an int.
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public const int LAT_MSP_VALUE = self::LAT_INTEGER_MULTIPLIER * OpenLocationCode::ENCODING_BASE * OpenLocationCode::ENCODING_BASE;
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// Value of the most significant longitude digit after it has been converted to an integer.
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// Note: since we are using 64-bit PHP, this can be an int.
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public const int LNG_MSP_VALUE = self::LNG_INTEGER_MULTIPLIER * OpenLocationCode::ENCODING_BASE * OpenLocationCode::ENCODING_BASE;
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public function __construct()
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{
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if (PHP_INT_SIZE < 8) {
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// 32-bit PHP has 32-bit int, which uses 4 bytes i.e. PHP_INT_SIZE = 4
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throw new RuntimeException("CodeCalculatorInt cannot be used due to bad PHP_INT_MAX value. Use CodeCalculatorFloat instead.");
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}
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}
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protected function generateRevOlcCode(float $latitude, float $longitude, int $codeLength): string
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{
33+
// PHP has native support for string concatenation, and string reversal is quite fast.
34+
$revCode = "";
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// Compute the code.
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// The idea of this approach is to convert each value to an integer
38+
// after multiplying it by the final precision.
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// This allows us to use only integer operations, so
40+
// avoiding any accumulation of floating point representation errors.
41+
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// Multiply values by their precision and convert to positive.
43+
// Rounding avoids/minimises errors due to floating point precision.
44+
$latVal = intdiv((int) round(($latitude + OpenLocationCode::LATITUDE_MAX) * self::LAT_INTEGER_MULTIPLIER * 1e6), 1e6);
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$lngVal = intdiv((int) round(($longitude + OpenLocationCode::LONGITUDE_MAX) * self::LNG_INTEGER_MULTIPLIER * 1e6), 1e6);
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// Compute the grid part of the code if necessary.
48+
if ($codeLength > OpenLocationCode::PAIR_CODE_LENGTH) {
49+
for ($i = 0; $i < OpenLocationCode::GRID_CODE_LENGTH; $i++) {
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$latDigit = $latVal % OpenLocationCode::GRID_ROWS;
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$lngDigit = $lngVal % OpenLocationCode::GRID_COLUMNS;
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$ndx = $latDigit * OpenLocationCode::GRID_COLUMNS + $lngDigit;
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$revCode .= OpenLocationCode::CODE_ALPHABET[$ndx];
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$latVal = intdiv($latVal, OpenLocationCode::GRID_ROWS);
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$lngVal = intdiv($lngVal, OpenLocationCode::GRID_COLUMNS);
56+
}
57+
unset($i, $latDigit, $lngDigit, $ndx);
58+
} else {
59+
$latVal = (int) ($latVal / pow(OpenLocationCode::GRID_ROWS, OpenLocationCode::GRID_CODE_LENGTH));
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$lngVal = (int) ($lngVal / pow(OpenLocationCode::GRID_COLUMNS, OpenLocationCode::GRID_CODE_LENGTH));
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}
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// Compute the pair section of the code.
64+
for ($i = 0; $i < intdiv(OpenLocationCode::PAIR_CODE_LENGTH, 2); $i++) {
65+
$revCode .= OpenLocationCode::CODE_ALPHABET[$lngVal % OpenLocationCode::ENCODING_BASE];
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$revCode .= OpenLocationCode::CODE_ALPHABET[$latVal % OpenLocationCode::ENCODING_BASE];
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$latVal = intdiv($latVal, OpenLocationCode::ENCODING_BASE);
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$lngVal = intdiv($lngVal, OpenLocationCode::ENCODING_BASE);
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// If we are at the separator position, add the separator
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if ($i == 0) {
71+
$revCode .= OpenLocationCode::SEPARATOR;
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}
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}
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return $revCode;
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}
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protected function generateCodeArea(string $strippedCode): CodeArea
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{
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// Initialize the values.
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$latVal = -OpenLocationCode::LATITUDE_MAX * self::LAT_INTEGER_MULTIPLIER;
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$lngVal = -OpenLocationCode::LONGITUDE_MAX * self::LNG_INTEGER_MULTIPLIER;
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// Define the place value for the digits. We'll divide this down as we work through the code.
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$latPlaceVal = self::LAT_MSP_VALUE;
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$lngPlaceVal = self::LNG_MSP_VALUE;
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for ($i = OpenLocationCode::PAIR_CODE_LENGTH; $i < min(strlen($strippedCode), OpenLocationCode::MAX_DIGIT_COUNT); $i += 2) {
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$latPlaceVal = intdiv($latPlaceVal, OpenLocationCode::ENCODING_BASE);
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$lngPlaceVal = intdiv($lngPlaceVal, OpenLocationCode::ENCODING_BASE);
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$latVal += strpos(OpenLocationCode::CODE_ALPHABET, $strippedCode[$i]) * $latPlaceVal;
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$lngVal = strpos(OpenLocationCode::CODE_ALPHABET, $strippedCode[$i + 1]) * $lngPlaceVal;
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}
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unset($i);
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for ($i = OpenLocationCode::PAIR_CODE_LENGTH; $i < min(strlen($strippedCode), OpenLocationCode::MAX_DIGIT_COUNT); $i++) {
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$latPlaceVal = intdiv($latPlaceVal, OpenLocationCode::GRID_ROWS);
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$lngPlaceVal = intdiv($lngPlaceVal, OpenLocationCode::GRID_COLUMNS);
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$digit = strpos(OpenLocationCode::CODE_ALPHABET, $strippedCode[$i]);
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$row = intdiv($digit, OpenLocationCode::GRID_COLUMNS);
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$col = $digit % OpenLocationCode::GRID_COLUMNS;
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$latVal += $row * $latPlaceVal;
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$lngVal += $col * $lngPlaceVal;
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unset($digit);
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}
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unset($i);
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$latitudeLo = $latVal / self::LAT_INTEGER_MULTIPLIER;
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$longitudeLo = $lngVal / self::LNG_INTEGER_MULTIPLIER;
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$latitudeHi = ($latVal + $latPlaceVal) / self::LAT_INTEGER_MULTIPLIER;
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$longitudeHi = ($lngVal + $lngPlaceVal) / self::LNG_INTEGER_MULTIPLIER;
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return new CodeArea(
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$latitudeLo,
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$longitudeLo,
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$latitudeHi,
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$longitudeHi,
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min(strlen($strippedCode), OpenLocationCode::MAX_DIGIT_COUNT),
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);
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}
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}

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