Correctly round rounding mode with zero edge case

Author: SakiTakamachi

NEWS

@@ -2,6 +2,10 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.4.3
 
+- BcMath:
+  . Fixed bug GH-17064 (Correctly round rounding mode with zero edge case).
+    (Saki Takamachi)
+
 - Streams:
   . Fixed bug GH-17037 (UAF in user filter when adding existing filter name due
     to incorrect error handling). (nielsdos)

ext/bcmath/libbcmath/src/round.c

@@ -33,10 +33,45 @@ void bc_round(bc_num num, zend_long precision, zend_long mode, bc_num *result)
 	* - If the fractional part ends with zeros, the zeros are omitted and the number of digits in num is reduced.
 	*   Meaning we might end up in the previous case.
 	*/
+
+	/* e.g. value is 0.1 and precision is -3, ret is 0 or 1000  */
 	if (precision < 0 && num->n_len < (size_t) (-(precision + Z_L(1))) + 1) {
-		*result = bc_copy_num(BCG(_zero_));
+		switch (mode) {
+			case PHP_ROUND_HALF_UP:
+			case PHP_ROUND_HALF_DOWN:
+			case PHP_ROUND_HALF_EVEN:
+			case PHP_ROUND_HALF_ODD:
+			case PHP_ROUND_TOWARD_ZERO:
+				*result = bc_copy_num(BCG(_zero_));
+				return;
+
+			case PHP_ROUND_CEILING:
+				if (num->n_sign == MINUS) {
+					*result = bc_copy_num(BCG(_zero_));
+					return;
+				}
+				break;
+
+			case PHP_ROUND_FLOOR:
+				if (num->n_sign == PLUS) {
+					*result = bc_copy_num(BCG(_zero_));
+					return;
+				}
+				break;
+
+			case PHP_ROUND_AWAY_FROM_ZERO:
+				break;
+
+			EMPTY_SWITCH_DEFAULT_CASE()
+		}
+
+		/* If precision is -3, it becomes 1000. */
+		*result = bc_new_num(-precision + 1, 0);
+		(*result)->n_value[0] = 1;
+		(*result)->n_sign = num->n_sign;
 		return;
 	}
+
 	/* Just like bcadd('1', '1', 4) becomes '2.0000', it pads with zeros at the end if necessary. */
 	if (precision >= 0 && num->n_scale <= precision) {
 		if (num->n_scale == precision) {
@@ -61,7 +96,7 @@ void bc_round(bc_num num, zend_long precision, zend_long mode, bc_num *result)
 	 * If the result of rounding is carried over, it will be added later, so first set it to 0 here.
 	 */
 	if (rounded_len == 0) {
-		*result = bc_copy_num(BCG(_zero_));
+		*result = bc_new_num(1, 0);
 	} else {
 		*result = bc_new_num(num->n_len, precision > 0 ? precision : 0);
 		memcpy((*result)->n_value, num->n_value, rounded_len);

ext/bcmath/tests/bcround_away_from_zero.phpt

@@ -27,6 +27,8 @@ run_round_test(RoundingMode::AwayFromZero);
         [-1.9, 0] => -2
 
 ========== minus precision ==========
+       [0.01, -3] => 1000
+      [-0.01, -3] => -1000
          [50, -2] => 100
         [-50, -2] => -100
        [1230, -1] => 1230

ext/bcmath/tests/bcround_ceiling.phpt

@@ -27,6 +27,8 @@ run_round_test(RoundingMode::PositiveInfinity);
         [-1.9, 0] => -1
 
 ========== minus precision ==========
+       [0.01, -3] => 1000
+      [-0.01, -3] => 0
          [50, -2] => 100
         [-50, -2] => 0
        [1230, -1] => 1230

ext/bcmath/tests/bcround_early_return.phpt

@@ -6,15 +6,11 @@ bcmath
 <?php
 
 $early_return_cases = [
-    ['123', -4],
-    ['123.123456', -4],
     ['123', 1],
     ['123.5', 1],
     ['123.5', 2],
     ['123.0000000000000000000001', 22],
     ['123.0000000000000000000001', 23],
-    ['-123', -4],
-    ['-123.123456', -4],
     ['-123', 1],
     ['-123.5', 1],
     ['-123.5', 2],
@@ -54,15 +50,11 @@ foreach (RoundingMode::cases() as $mode) {
 }
 ?>
 --EXPECT--
-                        [123, -4] => 0
-                 [123.123456, -4] => 0
                          [123, 1] => 123.0
                        [123.5, 1] => 123.5
                        [123.5, 2] => 123.50
  [123.0000000000000000000001, 22] => 123.0000000000000000000001
  [123.0000000000000000000001, 23] => 123.00000000000000000000010
-                       [-123, -4] => 0
-                [-123.123456, -4] => 0
                         [-123, 1] => -123.0
                       [-123.5, 1] => -123.5
                       [-123.5, 2] => -123.50

ext/bcmath/tests/bcround_floor.phpt

@@ -27,6 +27,8 @@ run_round_test(RoundingMode::NegativeInfinity);
         [-1.9, 0] => -2
 
 ========== minus precision ==========
+       [0.01, -3] => 0
+      [-0.01, -3] => -1000
          [50, -2] => 0
         [-50, -2] => -100
        [1230, -1] => 1230

ext/bcmath/tests/bcround_half_down.phpt

@@ -27,6 +27,8 @@ run_round_test(RoundingMode::HalfTowardsZero);
         [-1.9, 0] => -2
 
 ========== minus precision ==========
+       [0.01, -3] => 0
+      [-0.01, -3] => 0
          [50, -2] => 0
         [-50, -2] => 0
        [1230, -1] => 1230

ext/bcmath/tests/bcround_half_even.phpt

@@ -27,6 +27,8 @@ run_round_test(RoundingMode::HalfEven);
         [-1.9, 0] => -2
 
 ========== minus precision ==========
+       [0.01, -3] => 0
+      [-0.01, -3] => 0
          [50, -2] => 0
         [-50, -2] => 0
        [1230, -1] => 1230

ext/bcmath/tests/bcround_half_odd.phpt

@@ -27,6 +27,8 @@ run_round_test(RoundingMode::HalfOdd);
         [-1.9, 0] => -2
 
 ========== minus precision ==========
+       [0.01, -3] => 0
+      [-0.01, -3] => 0
          [50, -2] => 100
         [-50, -2] => -100
        [1230, -1] => 1230

ext/bcmath/tests/bcround_half_up.phpt

@@ -27,6 +27,8 @@ run_round_test(RoundingMode::HalfAwayFromZero);
         [-1.9, 0] => -2
 
 ========== minus precision ==========
+       [0.01, -3] => 0
+      [-0.01, -3] => 0
          [50, -2] => 100
         [-50, -2] => -100
        [1230, -1] => 1230

ext/bcmath/tests/bcround_test_helper.inc

@@ -30,6 +30,8 @@ function run_round_test(RoundingMode $mode)
     ];
 
     $minus_precision_cases = [
+        ['0.01', -3],
+        ['-0.01', -3],
         ['50', -2],
         ['-50', -2],
         ['1230', -1],

ext/bcmath/tests/bcround_toward_zero.phpt

@@ -27,6 +27,8 @@ run_round_test(RoundingMode::TowardsZero);
         [-1.9, 0] => -1
 
 ========== minus precision ==========
+       [0.01, -3] => 0
+      [-0.01, -3] => 0
          [50, -2] => 0
         [-50, -2] => 0
        [1230, -1] => 1230

ext/bcmath/tests/number/methods/round.phpt

@@ -19,11 +19,13 @@ foreach (RoundingMode::cases() as $mode) {
         '2.5',
         '-2.5',
     ] as $number) {
-        $func_ret = bcround($number, 0, $mode);
-        $method_ret = (new BcMath\Number($number))->round(0, $mode);
-        if ($method_ret->compare($func_ret) !== 0) {
-            echo "Result is incorrect.\n";
-            var_dump($number, $mode, $func_ret, $method_ret);
+        foreach ([0, 5, -5] as $scale) {
+            $func_ret = bcround($number, $scale, $mode);
+            $method_ret = (new BcMath\Number($number))->round($scale, $mode);
+            if ($method_ret->compare($func_ret) !== 0) {
+                echo "Result is incorrect.\n";
+                var_dump($number, $mode, $func_ret, $method_ret);
+            }
         }
     }
 }