Fix up rounding for small values.

composer.json

@@ -21,7 +21,7 @@
     "require-dev": {
         "php-collective/code-sniffer": "^0.2.1",
         "phpstan/phpstan": "^2.0.0",
-        "phpunit/phpunit": "^11.0.0"
+        "phpunit/phpunit": "^10.5.45 || ^11.0.0"
     },
     "minimum-stability": "stable",
     "prefer-stable": true,

phpstan.neon

@@ -5,4 +5,4 @@ parameters:
     ignoreErrors:
         - identifier: missingType.iterableValue
         - '#Unsafe usage of new static\(\).#'
-        - '#expects numeric-string, string given.#'
+        - '#expects numeric-string, .*string given.#'

src/Decimal.php

@@ -485,22 +485,44 @@ public function round(int $scale = 0, int $roundMode = self::ROUND_HALF_UP): sta
     {
         $exponent = $scale + 1;
 
-        $e = bcpow('10', (string)$exponent);
         switch ($roundMode) {
             case static::ROUND_FLOOR:
-                $v = bcdiv(bcadd(bcmul((string)$this, $e, 0), $this->isNegative() ? '-9' : '0'), $e, 0);
+                $stringValue = (string)$this;
 
-                break;
+                // If already an integer, return as is
+                if (!str_contains($stringValue, '.')) {
+                    return new static($stringValue, $scale);
+                }
+
+                // For positive values, truncate the decimal part (round down)
+                if (!$this->isNegative()) {
+                    return new static(bcsub($stringValue, bcmod($stringValue, '1'), 0), $scale);
+                }
+
+                // For negative values, round down away from zero
+                return new static(bcsub($stringValue, '1', 0), $scale);
             case static::ROUND_CEIL:
-                $v = bcdiv(bcadd(bcmul((string)$this, $e, 0), $this->isNegative() ? '0' : '9'), $e, 0);
+                $stringValue = (string)$this;
+
+                // If already an integer, return as is
+                if (!str_contains($stringValue, '.')) {
+                    return new static($stringValue, $scale);
+                }
+
+                // If negative, truncate (remove decimals without adding 1)
+                if ($this->isNegative()) {
+                    return new static(bcsub($stringValue, '0', 0), $scale);
+                }
 
-                break;
+                // Otherwise, round up for positive numbers
+                return new static(bcadd($stringValue, '1', 0), $scale);
             case static::ROUND_HALF_UP:
             default:
+                $e = bcpow('10', (string)$exponent);
                 $v = bcdiv(bcadd(bcmul((string)$this, $e, 0), $this->isNegative() ? '-5' : '5'), $e, $scale);
         }
 
-        return new static($v);
+        return new static($v, $scale);
     }
 
     /**

tests/DecimalTest.php

@@ -636,7 +636,12 @@ public function testRound(mixed $value, int $scale, string $expected): void
      */
     protected function assertNativeRound(string $expected, mixed $value, int $scale, int $roundMode): void
     {
-        $this->assertSame((new Decimal($expected))->trim()->toString(), (string)round((float)$value, $scale, $roundMode));
+        $value = (string)round((float)$value, $scale, $roundMode);
+        if ($value === '-0') {
+            $value = '0';
+        }
+
+        $this->assertSame((new Decimal($expected))->trim()->toString(), $value);
     }
 
     /**
@@ -659,6 +664,10 @@ public static function roundProvider(): array
             [13.4999, 0, '13'],
             [13.4999, 10, '13.4999000000'],
             [13.4999, 2, '13.50'],
+            [0.0001, 0, '0'],
+            [-0.0001, 0, '0'],
+            [0.9999, 0, '1'],
+            [-0.9999, 0, '-1'],
         ];
     }
 
@@ -685,7 +694,12 @@ public function testFloor(mixed $value, string $expected): void
      */
     protected function assertNativeFloor(string $expected, mixed $value): void
     {
-        $this->assertSame($expected, (string)floor((float)$value));
+        $value = (string)floor((float)$value);
+        if ($value === '-0') {
+            $value = '0';
+        }
+
+        $this->assertSame($expected, $value);
     }
 
     /**
@@ -706,6 +720,8 @@ public static function floorProvider(): array
             ['13.6999', '13'],
             ['13.1', '13'],
             ['13.9', '13'],
+            [0.0001, '0'],
+            [-0.0001, '-1'],
         ];
     }
 
@@ -732,7 +748,11 @@ public function testCeil(mixed $value, string $expected): void
      */
     protected function assertNativeCeil(string $expected, mixed $value): void
     {
-        $this->assertSame($expected, (string)ceil((float)$value));
+        $value = (string)ceil((float)$value);
+        if ($value === '-0') {
+            $value = '0';
+        }
+        $this->assertSame($expected, $value);
     }
 
     /**
@@ -753,6 +773,8 @@ public static function ceilProvider(): array
             ['13.6999', '14'],
             ['13.1', '14'],
             ['13.9', '14'],
+            [0.0001, '1'],
+            [-0.0001, '0'],
         ];
     }