random: Randomizer::getFloat(): Fix check for empty open intervals (#10185)

* random: Randomizer::getFloat(): Fix check for empty open intervals

The check for invalid parameters for the IntervalBoundary::OpenOpen variant was
not correct: If two consecutive doubles are passed as parameters, the resulting
interval is empty, resulting in an uint64 underflow in the γ-section
implementation.

Instead of checking whether `$min < $max`, we must check that there is at least
one more double between `$min` and `$max`, i.e. it must hold that:

	nextafter($min, $max) != $max

Instead of duplicating the comparatively complicated and expensive `nextafter`
logic for a rare error case we instead return `NAN` from the γ-section
implementation when the parameters result in an empty interval and thus underflow.

This allows us to reliably detect this specific error case *after* the fact,
but without modifying the engine state. It also provides reliable error
reporting for other internal functions that might use the γ-section
implementation.

* random: γ-section: Also check that that min is smaller than max

This extends the empty-interval check in the γ-section implementation with a
check that min is actually the smaller of the two parameters.

* random: Use PHP_FLOAT_EPSILON in getFloat_error.phpt

Co-authored-by: Christoph M. Becker <cmbecker69@gmx.de>

Author: TimWolla

ext/random/gammasection.c

@@ -66,6 +66,11 @@ PHPAPI double php_random_gammasection_closed_open(const php_random_algo *algo, p
 {
 	double g = gamma_max(min, max);
 	uint64_t hi = ceilint(min, max, g);
+
+	if (UNEXPECTED(max <= min || hi < 1)) {
+		return NAN;
+	}
+
 	uint64_t k = 1 + php_random_range64(algo, status, hi - 1); /* [1, hi] */
 
 	if (fabs(min) <= fabs(max)) {
@@ -79,6 +84,11 @@ PHPAPI double php_random_gammasection_closed_closed(const php_random_algo *algo,
 {
 	double g = gamma_max(min, max);
 	uint64_t hi = ceilint(min, max, g);
+
+	if (UNEXPECTED(max < min)) {
+		return NAN;
+	}
+
 	uint64_t k = php_random_range64(algo, status, hi); /* [0, hi] */
 
 	if (fabs(min) <= fabs(max)) {
@@ -92,6 +102,11 @@ PHPAPI double php_random_gammasection_open_closed(const php_random_algo *algo, p
 {
 	double g = gamma_max(min, max);
 	uint64_t hi = ceilint(min, max, g);
+
+	if (UNEXPECTED(max <= min || hi < 1)) {
+		return NAN;
+	}
+
 	uint64_t k = php_random_range64(algo, status, hi - 1); /* [0, hi - 1] */
 
 	if (fabs(min) <= fabs(max)) {
@@ -105,6 +120,11 @@ PHPAPI double php_random_gammasection_open_open(const php_random_algo *algo, php
 {
 	double g = gamma_max(min, max);
 	uint64_t hi = ceilint(min, max, g);
+
+	if (UNEXPECTED(max <= min || hi < 2)) {
+		return NAN;
+	}
+
 	uint64_t k = 1 + php_random_range64(algo, status, hi - 2); /* [1, hi - 1] */
 
 	if (fabs(min) <= fabs(max)) {

ext/random/randomizer.c

@@ -190,7 +190,14 @@ PHP_METHOD(Random_Randomizer, getFloat)
 			RETURN_THROWS();
 		}
 
-		RETURN_DOUBLE(php_random_gammasection_open_open(randomizer->algo, randomizer->status, min, max));
+		RETVAL_DOUBLE(php_random_gammasection_open_open(randomizer->algo, randomizer->status, min, max));
+
+		if (UNEXPECTED(isnan(Z_DVAL_P(return_value)))) {
+			zend_value_error("The given interval is empty, there are no floats between argument #1 ($min) and argument #2 ($max).");
+			RETURN_THROWS();
+		}
+
+		return;
 	default:
 		ZEND_UNREACHABLE();
 	}

ext/random/tests/03_randomizer/methods/getFloat_error.phpt

@@ -73,10 +73,17 @@ foreach ([
     } catch (ValueError $e) {
         echo $e->getMessage(), PHP_EOL;
     }
+
+    try {
+        // There is no float between the two parameters, thus making the OpenOpen interval empty.
+        var_dump(randomizer()->getFloat(1.0, 1 + PHP_FLOAT_EPSILON, $boundary));
+    } catch (ValueError $e) {
+        echo $e->getMessage(), PHP_EOL;
+    }
 }
 
 ?>
---EXPECT--
+--EXPECTF--
 ClosedClosed
 Random\Randomizer::getFloat(): Argument #1 ($min) must be finite
 Random\Randomizer::getFloat(): Argument #1 ($min) must be finite
@@ -87,6 +94,7 @@ Random\Randomizer::getFloat(): Argument #2 ($max) must be finite
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than or equal to argument #1 ($min)
 float(0)
 float(1.0E+17)
+float(%f)
 ClosedOpen
 Random\Randomizer::getFloat(): Argument #1 ($min) must be finite
 Random\Randomizer::getFloat(): Argument #1 ($min) must be finite
@@ -97,6 +105,7 @@ Random\Randomizer::getFloat(): Argument #2 ($max) must be finite
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than argument #1 ($min)
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than argument #1 ($min)
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than argument #1 ($min)
+float(1)
 OpenClosed
 Random\Randomizer::getFloat(): Argument #1 ($min) must be finite
 Random\Randomizer::getFloat(): Argument #1 ($min) must be finite
@@ -107,6 +116,7 @@ Random\Randomizer::getFloat(): Argument #2 ($max) must be finite
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than argument #1 ($min)
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than argument #1 ($min)
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than argument #1 ($min)
+float(1.0000000000000002)
 OpenOpen
 Random\Randomizer::getFloat(): Argument #1 ($min) must be finite
 Random\Randomizer::getFloat(): Argument #1 ($min) must be finite
@@ -117,3 +127,4 @@ Random\Randomizer::getFloat(): Argument #2 ($max) must be finite
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than argument #1 ($min)
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than argument #1 ($min)
 Random\Randomizer::getFloat(): Argument #2 ($max) must be greater than argument #1 ($min)
+The given interval is empty, there are no floats between argument #1 ($min) and argument #2 ($max).