New Algorithm for TRUNC, ROUNDUP, and ROUNDDOWN

Fix #4113. TRUNC isn't always producing the expected result. There was a promising algorithm at https://stackoverflow.com/questions/4668628/truncate-float-numbers-with-php from user Juan. It works through Php8.3, but failed in Php8.4 (more on this later). User Savageman on the same page has a solution that needs work, but, once the work had taken place, it works on Php8.1-8.4.

The ROUNDUP and ROUNDDOWN functions were adversely affected by Php8.4, probably for the same reasons as Juan's TRUNC suggestion. I put a kludge in place for them some time ago, but I wasn't happy with it. The solution used for TRUNC here suggested a change to the ROUNDUP and ROUNDDOWN code that would no longer require the kludge. The change to those functions now works more cleanly on Php8.1-8.4.

src/PhpSpreadsheet/Calculation/MathTrig/Round.php

@@ -10,8 +10,6 @@ class Round
 {
     use ArrayEnabled;
 
-    private const ROUNDING_ADJUSTMENT = (PHP_VERSION_ID < 80400) ? 0 : 1e-14;
-
     /**
      * ROUND.
      *
@@ -69,11 +67,22 @@ class Round
             return 0.0;
         }
 
+        $digitsPlus1 = $digits + 1;
         if ($number < 0.0) {
-            return round($number - 0.5 * 0.1 ** $digits + self::ROUNDING_ADJUSTMENT, $digits, PHP_ROUND_HALF_DOWN);
+            if ($digitsPlus1 < 0) {
+                return round($number - 0.5 * 0.1 ** $digits, $digits, PHP_ROUND_HALF_DOWN);
+            }
+            $result = sprintf("%.{$digitsPlus1}f", $number - 0.5 * 0.1 ** $digits);
+
+            return round((float) $result, $digits, PHP_ROUND_HALF_DOWN);
         }
 
-        return round($number + 0.5 * 0.1 ** $digits - self::ROUNDING_ADJUSTMENT, $digits, PHP_ROUND_HALF_DOWN);
+        if ($digitsPlus1 < 0) {
+            return round($number + 0.5 * 0.1 ** $digits, $digits, PHP_ROUND_HALF_DOWN);
+        }
+        $result = sprintf("%.{$digitsPlus1}f", $number + 0.5 * 0.1 ** $digits);
+
+        return round((float) $result, $digits, PHP_ROUND_HALF_DOWN);
     }
 
     /**
@@ -105,11 +114,23 @@ class Round
             return 0.0;
         }
 
+        $digitsPlus1 = $digits + 1;
         if ($number < 0.0) {
-            return round($number + 0.5 * 0.1 ** $digits - self::ROUNDING_ADJUSTMENT, $digits, PHP_ROUND_HALF_UP);
+            if ($digitsPlus1 < 0) {
+                return round($number + 0.5 * 0.1 ** $digits, $digits, PHP_ROUND_HALF_UP);
+            }
+            $result = sprintf("%.{$digitsPlus1}f", $number + 0.5 * 0.1 ** $digits);
+
+            return round((float) $result, $digits, PHP_ROUND_HALF_UP);
         }
 
-        return round($number - 0.5 * 0.1 ** $digits + self::ROUNDING_ADJUSTMENT, $digits, PHP_ROUND_HALF_UP);
+        if ($digitsPlus1 < 0) {
+            return round($number - 0.5 * 0.1 ** $digits, $digits, PHP_ROUND_HALF_UP);
+        }
+
+        $result = sprintf("%.{$digitsPlus1}f", $number - 0.5 * 0.1 ** $digits);
+
+        return round((float) $result, $digits, PHP_ROUND_HALF_UP);
     }
 
     /**

src/PhpSpreadsheet/Calculation/MathTrig/Trunc.php

@@ -34,15 +34,26 @@ class Trunc
             return $e->getMessage();
         }
 
-        $digits = floor($digits);
-
-        // Truncate
-        $adjust = 10 ** $digits;
-
-        if (($digits > 0) && (rtrim((string) (int) ((abs($value) - abs((int) $value)) * $adjust), '0') < $adjust / 10)) {
+        if ($value == 0) {
             return $value;
         }
 
-        return ((int) ($value * $adjust)) / $adjust;
+        if ($value >= 0) {
+            $minusSign = '';
+        } else {
+            $minusSign = '-';
+            $value = -$value;
+        }
+        $digits = (int) floor($digits);
+        if ($digits < 0) {
+            $power = (int) (10 ** -$digits);
+            $result = intdiv((int) floor($value), $power) * $power;
+
+            return ($minusSign === '') ? $result : -$result;
+        }
+        $digitsPlus1 = $digits + 1;
+        $result = substr($minusSign . sprintf("%.{$digitsPlus1}f", $value), 0, -1);
+
+        return (float) $result;
     }
 }

tests/data/Calculation/MathTrig/ROUNDDOWN.php

@@ -33,4 +33,5 @@ return [
     [0, 'B1, 0'],
     ['exception', ''],
     ['exception', '35.51'],
+    'negative number and precision' => [-31400, '-31415.92654, -2'],
 ];

tests/data/Calculation/MathTrig/ROUNDUP.php

@@ -33,4 +33,5 @@ return [
     [0, 'B1, 0'],
     ['exception', ''],
     ['exception', '35.51'],
+    'negative number and precision' => [-31500, '-31415.92654, -2'],
 ];

tests/data/Calculation/MathTrig/TRUNC.php

@@ -11,6 +11,7 @@ return [
     [-31415.92654, '-31415.92654, 10'],
     [31415.92, '31415.92654, 2'],
     [31400, '31415.92654, -2'],
+    'negative number and precision' => [-31400, '-31415.92654, -2'],
     [0, '31415.92654, -10'],
     [0, '-31415.92654, -10'],
     [12000, '12345.6789, -3'],
@@ -32,4 +33,12 @@ return [
     [-3, 'A4'],
     [-5, 'A5'],
     [0, 'B1'],
+    'issue4113' => [1.0, '1.01, 1'],
+    'issue4113 negative' => [-1.0, '-1.01, 1'],
+    'issue4113 additional' => [10.04, '10.04, 2'],
+    'issue4113 additional negative' => [-10.04, '-10.04, 2'],
+    'issue4113 small fraction keep all' => [0.04, '0.04, 2'],
+    'issue4113 small negative fraction keep all' => [-0.04, '-0.04, 2'],
+    'issue4113 small fraction lose some' => [0.0, '0.01, 1'],
+    'issue4113 small negative fraction lose some' => [0.0, '-0.001, 1'],
 ];