Remove vestigial code and improve check

This code didn't make sense given that we couldn't use an integer
bigger than PHP_INT_MAX when reading from the file. I suspect we used to
inline more of the actual decoding of the value.

Author: oschwald

CHANGELOG.md

@@ -1,6 +1,13 @@
 CHANGELOG
 =========
 
+1.10.1
+-------------------
+
+* Fix a `TypeError` exception in the pure PHP reader when using large
+  databases on 32-bit PHP builds with the `bcmath` extension. Reported
+  by dodo1708. GitHub #124.
+
 1.10.0 (2021-02-09)
 -------------------
 

src/MaxMind/Db/Reader/Decoder.php

@@ -286,17 +286,13 @@ private function decodePointer(int $ctrlByte, int $offset): array
                 // machines
                 $pointerOffset = $this->decodeUint($buffer, $pointerSize);
 
-                $byteLength = $pointerSize + $this->pointerBaseByteSize;
-
-                if ($byteLength <= _MM_MAX_INT_BYTES) {
-                    $pointer = $pointerOffset + $this->pointerBase;
-                } elseif (\extension_loaded('gmp')) {
-                    $pointer = gmp_strval(gmp_add($pointerOffset, $this->pointerBase));
-                } elseif (\extension_loaded('bcmath')) {
-                    $pointer = bcadd($pointerOffset, (string) $this->pointerBase);
+                $pointerBase = $this->pointerBase;
+
+                if (\PHP_INT_MAX - $pointerBase >= $pointerOffset) {
+                    $pointer = $pointerOffset + $pointerBase;
                 } else {
                     throw new RuntimeException(
-                        'The gmp or bcmath extension must be installed to read this database.'
+                        'The database offset is too large to be represented on your platform.'
                     );
                 }
 

tests/MaxMind/Db/Test/Reader/DecoderTest.php

@@ -159,7 +159,7 @@ class DecoderTest extends TestCase
      */
     private function pointers(): array
     {
-        return [
+        $v = [
             ['expected' => 0, 'input' => [0x20, 0x0]],
             ['expected' => 5, 'input' => [0x20, 0x5]],
             ['expected' => 10, 'input' => [0x20, 0xa]],
@@ -168,9 +168,14 @@ private function pointers(): array
             ['expected' => 524283, 'input' => [0x2f, 0xf7, 0xfb]],
             ['expected' => 526335, 'input' => [0x2f, 0xff, 0xff]],
             ['expected' => 134217726, 'input' => [0x37, 0xf7, 0xf7, 0xfe]],
-            ['expected' => \PHP_INT_MAX < 4294967295 ? '2147483647' : 2147483647, 'input' => [0x38, 0x7f, 0xff, 0xff, 0xff]],
-            ['expected' => \PHP_INT_MAX < 4294967295 ? '4294967295' : 4294967295, 'input' => [0x38, 0xff, 0xff, 0xff, 0xff]],
+            ['expected' => 2147483647, 'input' => [0x38, 0x7f, 0xff, 0xff, 0xff]],
         ];
+
+        if (\PHP_INT_MAX > 4294967295) {
+            array_push($v, ['expected' => 4294967295, 'input' => [0x38, 0xff, 0xff, 0xff, 0xff]]);
+        }
+
+        return $v;
     }
 
     /**