Too Many Digits

We can't handle more digits than Php allows. Neither can Excel. Just do our best without throwing an Error.

src/PhpSpreadsheet/Calculation/MathTrig/Trunc.php

@@ -13,6 +13,11 @@ class Trunc
      * TRUNC.
      *
      * Truncates value to the number of fractional digits by number_digits.
+     * This will probably not be the precise result in the unlikely
+     * event that the number of digits to the left of the decimal
+     * plus the number of digits to the right exceeds PHP_FLOAT_DIG
+     * (or possibly that value minus 1).
+     * Excel is unlikely to do any better.
      *
      * @param array|float $value Or can be an array of values
      * @param array|int $digits Or can be an array of values
@@ -52,7 +57,7 @@ public static function evaluate(array|float|string|null $value = 0, array|int|st
             return ($minusSign === '') ? $result : -$result;
         }
         $decimals = PHP_FLOAT_DIG - strlen((string) (int) $value);
-        $resultString = sprintf('%.' . $decimals . 'F', $value);
+        $resultString = ($decimals < 0) ? sprintf('%F', $value) : sprintf('%.' . $decimals . 'F', $value);
         $regExp = '/([.]\\d{' . $digits . '})\\d+$/';
         $result = $minusSign . (preg_replace($regExp, '$1', $resultString) ?? $resultString);
 

tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TruncTest.php

@@ -47,4 +47,36 @@ public static function providerTruncArray(): array
             'matrix' => [[[3.14, 3.141], [3.14159, 3.14159265]], '3.1415926536', '{2, 3; 5, 8}'],
         ];
     }
+
+    public function testTooMuchPrecision(): void
+    {
+        // This test is pretty screwy. Possibly shouldn't even attempt it.
+        // At any rate, these results seem to indicate that PHP
+        // maximum precision is PHP_FLOAT_DIG - 1 digits, not PHP_FLOAT_DIG.
+        // If that changes, at least one of these tests will have to change.
+        $sheet = $this->getSheet();
+        $sheet->getCell('E1')->setValue(10.0 ** (PHP_FLOAT_DIG - 3) + 1.2);
+        $sheet->getCell('E2')->setValue('=TRUNC(E1,1)');
+        $result = $sheet->getCell('E2')->getCalculatedValue();
+        $expectedResult = '1' . str_repeat('0', PHP_FLOAT_DIG - 4) . '1.2';
+        self::assertSame($expectedResult, (string) $result);
+
+        $sheet->getCell('F1')->setValue(10.0 ** (PHP_FLOAT_DIG - 2) + 1.2);
+        $sheet->getCell('F2')->setValue('=TRUNC(F1,1)');
+        $result = $sheet->getCell('F2')->getCalculatedValue();
+        $expectedResult = '1' . str_repeat('0', PHP_FLOAT_DIG - 3) . '1';
+        self::assertSame($expectedResult, (string) $result);
+
+        $sheet->getCell('G1')->setValue(10.0 ** (PHP_FLOAT_DIG - 1) + 1.2);
+        $sheet->getCell('G2')->setValue('=TRUNC(G1,1)');
+        $result = $sheet->getCell('G2')->getCalculatedValue();
+        $expectedResult = '1.0E+' . (PHP_FLOAT_DIG - 1);
+        self::assertSame($expectedResult, (string) $result);
+
+        $sheet->getCell('H1')->setValue(10.0 ** PHP_FLOAT_DIG + 1.2);
+        $sheet->getCell('H2')->setValue('=TRUNC(H1,1)');
+        $result = $sheet->getCell('H2')->getCalculatedValue();
+        $expectedResult = '1.0E+' . PHP_FLOAT_DIG;
+        self::assertSame($expectedResult, (string) $result);
+    }
 }