Optimize NativeCalculator::doDiv() (#87)

Author: Izumi-kun

src/Internal/Calculator/NativeCalculator.php

@@ -488,6 +488,22 @@ private function doDiv(string $a, string $b) : array
         $r = $a; // remainder
         $z = $y; // focus length, always $y or $y+1
 
+        /** @psalm-var numeric-string $b */
+        $nb = $b * 1; // cast to number
+        // performance optimization in cases where the remainder will never cause int overflow
+        if (is_int(($nb - 1) * 10 + 9)) {
+            $r = (int) \substr($a, 0, $z - 1);
+
+            for ($i = $z - 1; $i < $x; $i++) {
+                $n = $r * 10 + (int) $a[$i];
+                /** @psalm-var int $nb */
+                $q .= \intdiv($n, $nb);
+                $r = $n % $nb;
+            }
+
+            return [\ltrim($q, '0') ?: '0', (string) $r];
+        }
+
         for (;;) {
             $focus = \substr($a, 0, $z);
 

tests/BigIntegerTest.php

@@ -1253,6 +1253,9 @@ public static function providerQuotientAndRemainder() : array
             ['49283205308081983923480483094304390249024223', '-23981985358744892239240813', '-2055009398548863185', '20719258837232321643854818'],
             ['-8378278174814983902084304176539029302438924', '384758527893793829309012129991', '-21775419041855', '-367584271343844173835372665619'],
             ['-444444444444444444444444444444444444411111', '-33333333333333', '13333333333333466666666666667', '-33333333300000'],
+
+            ['922337203685477581000000000', '922337203685477580', '1000000000', '1000000000'],
+            ['922337203685477581000000000', '922337203685477581', '1000000000', '0'],
         ];
     }