Create CodeCalculatorInt

Author: Vectorial1024

src/CodeCalculator/CodeCalculatorInt.php

@@ -0,0 +1,116 @@
+<?php
+
+namespace Vectorial1024\OpenLocationCodePhp\CodeCalculator;
+
+use RuntimeException;
+use Vectorial1024\OpenLocationCodePhp\CodeArea;
+use Vectorial1024\OpenLocationCodePhp\OpenLocationCode;
+
+/**
+ * A Open Location Code calculator that uses "long" int.
+ * As such, this has ensured accuracy, but cannot be used in 32-bit PHP.
+ */
+class CodeCalculatorInt extends AbstractCodeCalculator
+{
+    // Value of the most significant latitude digit after it has been converted to an integer.
+    // Note: since we are using 64-bit PHP, this can be an int.
+    public const int LAT_MSP_VALUE = self::LAT_INTEGER_MULTIPLIER * OpenLocationCode::ENCODING_BASE * OpenLocationCode::ENCODING_BASE;
+
+    // Value of the most significant longitude digit after it has been converted to an integer.
+    // Note: since we are using 64-bit PHP, this can be an int.
+    public const int LNG_MSP_VALUE = self::LNG_INTEGER_MULTIPLIER * OpenLocationCode::ENCODING_BASE * OpenLocationCode::ENCODING_BASE;
+
+    public function __construct()
+    {
+        if (PHP_INT_SIZE < 8) {
+            // 32-bit PHP has 32-bit int, which uses 4 bytes i.e. PHP_INT_SIZE = 4
+            throw new RuntimeException("CodeCalculatorInt cannot be used due to bad PHP_INT_MAX value. Use CodeCalculatorFloat instead.");
+        }
+    }
+
+    protected function generateRevOlcCode(float $latitude, float $longitude, int $codeLength): string
+    {
+        // PHP has native support for string concatenation, and string reversal is quite fast.
+        $revCode = "";
+
+        // Compute the code.
+        // The idea of this approach is to convert each value to an integer 
+        // after multiplying it by the final precision. 
+        // This allows us to use only integer operations, so
+        // avoiding any accumulation of floating point representation errors.
+
+        // Multiply values by their precision and convert to positive.
+        // Rounding avoids/minimises errors due to floating point precision.
+        $latVal = intdiv((int) round(($latitude + OpenLocationCode::LATITUDE_MAX) * self::LAT_INTEGER_MULTIPLIER * 1e6), 1e6);
+        $lngVal = intdiv((int) round(($longitude + OpenLocationCode::LONGITUDE_MAX) * self::LNG_INTEGER_MULTIPLIER * 1e6), 1e6);
+
+        // Compute the grid part of the code if necessary.
+        if ($codeLength > OpenLocationCode::PAIR_CODE_LENGTH) {
+            for ($i = 0; $i < OpenLocationCode::GRID_CODE_LENGTH; $i++) {
+                $latDigit = $latVal % OpenLocationCode::GRID_ROWS;
+                $lngDigit = $lngVal % OpenLocationCode::GRID_COLUMNS;
+                $ndx = $latDigit * OpenLocationCode::GRID_COLUMNS + $lngDigit;
+                $revCode .= OpenLocationCode::CODE_ALPHABET[$ndx];
+                $latVal = intdiv($latVal, OpenLocationCode::GRID_ROWS);
+                $lngVal = intdiv($lngVal, OpenLocationCode::GRID_COLUMNS);
+            }
+            unset($i, $latDigit, $lngDigit, $ndx);
+        } else {
+            $latVal = (int) ($latVal / pow(OpenLocationCode::GRID_ROWS, OpenLocationCode::GRID_CODE_LENGTH));
+            $lngVal = (int) ($lngVal / pow(OpenLocationCode::GRID_COLUMNS, OpenLocationCode::GRID_CODE_LENGTH));
+        }
+
+        // Compute the pair section of the code.
+        for ($i = 0; $i < intdiv(OpenLocationCode::PAIR_CODE_LENGTH, 2); $i++) {
+            $revCode .= OpenLocationCode::CODE_ALPHABET[$lngVal % OpenLocationCode::ENCODING_BASE];
+            $revCode .= OpenLocationCode::CODE_ALPHABET[$latVal % OpenLocationCode::ENCODING_BASE];
+            $latVal = intdiv($latVal, OpenLocationCode::ENCODING_BASE);
+            $lngVal = intdiv($lngVal, OpenLocationCode::ENCODING_BASE);
+            // If we are at the separator position, add the separator
+            if ($i == 0) {
+                $revCode .= OpenLocationCode::SEPARATOR;
+            }
+        }
+
+        return $revCode;
+    }
+
+    public function decode(string $strippedCode): CodeArea
+    {
+        // Initialize the values. 
+        $latVal = -OpenLocationCode::LATITUDE_MAX * self::LAT_INTEGER_MULTIPLIER;
+        $lngVal = -OpenLocationCode::LONGITUDE_MAX * self::LNG_INTEGER_MULTIPLIER;
+        // Define the place value for the digits. We'll divide this down as we work through the code.
+        $latPlaceVal = self::LAT_MSP_VALUE;
+        $lngPlaceVal = self::LNG_MSP_VALUE;
+        for ($i = OpenLocationCode::PAIR_CODE_LENGTH; $i < min(strlen($strippedCode), OpenLocationCode::MAX_DIGIT_COUNT); $i += 2) {
+            $latPlaceVal = intdiv($latPlaceVal, OpenLocationCode::ENCODING_BASE);
+            $lngPlaceVal = intdiv($lngPlaceVal, OpenLocationCode::ENCODING_BASE);
+            $latVal += strpos(OpenLocationCode::CODE_ALPHABET, $strippedCode[$i]) * $latPlaceVal;
+            $lngVal = strpos(OpenLocationCode::CODE_ALPHABET, $strippedCode[$i + 1]) * $lngPlaceVal;
+        }
+        unset($i);
+        for ($i = OpenLocationCode::PAIR_CODE_LENGTH; $i < min(strlen($strippedCode), OpenLocationCode::MAX_DIGIT_COUNT); $i++) {
+            $latPlaceVal = intdiv($latPlaceVal, OpenLocationCode::GRID_ROWS);
+            $lngPlaceVal = intdiv($lngPlaceVal, OpenLocationCode::GRID_COLUMNS);
+            $digit = strpos(OpenLocationCode::CODE_ALPHABET, $strippedCode[$i]);
+            $row = intdiv($digit, OpenLocationCode::GRID_COLUMNS);
+            $col = $digit % OpenLocationCode::GRID_COLUMNS;
+            $latVal += $row * $latPlaceVal;
+            $lngVal += $col * $lngPlaceVal;
+            unset($digit);
+        }
+        unset($i);
+        $latitudeLo = $latVal / self::LAT_INTEGER_MULTIPLIER;
+        $longitudeLo = $lngVal / self::LNG_INTEGER_MULTIPLIER;
+        $latitudeHi = ($latVal + $latPlaceVal) / self::LAT_INTEGER_MULTIPLIER;
+        $longitudeHi = ($lngVal + $lngPlaceVal) / self::LNG_INTEGER_MULTIPLIER;
+        return new CodeArea(
+            $latitudeLo,
+            $longitudeLo,
+            $latitudeHi,
+            $longitudeHi,
+            min(strlen($strippedCode), OpenLocationCode::MAX_DIGIT_COUNT),
+        );
+    }
+}