From 9ad8aa762d7fb3e7eca2ce1c7e23d53b932da963 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tim=20D=C3=BCsterhus?= <tim@bastelstu.be>
Date: Sat, 23 Sep 2023 16:23:08 +0200
Subject: [PATCH] round: Bypass the precision logic when rounding to 0 places

Since GH-12220 the implementation of `php_round_helper()`, which performs
rounding to an integral value, is easy to verify for correctness up to the
floating point precision.

If rounding to 0 places is desired, i.e. the userland `round()` function is
called with `$precision = 0`, we bypass all logic for the decimal point
adjustment and instead directly call `php_round_helper()`.

This change fixes the remaining two cases of GH-12143 and likely guarantees
correct rounding for all possible inputs and `$precision = 0`.
---
 ext/standard/math.c                          |  4 +++
 ext/standard/tests/math/round_gh12143_5.phpt | 27 ++++++++++++++++++++
 ext/standard/tests/math/round_gh12143_6.phpt | 27 ++++++++++++++++++++
 3 files changed, 58 insertions(+)
 create mode 100644 ext/standard/tests/math/round_gh12143_5.phpt
 create mode 100644 ext/standard/tests/math/round_gh12143_6.phpt

diff --git a/ext/standard/math.c b/ext/standard/math.c
index 6b16b0755f69b..2f6743865b464 100644
--- a/ext/standard/math.c
+++ b/ext/standard/math.c
@@ -177,6 +177,10 @@ PHPAPI double _php_math_round(double value, int places, int mode) {
 		return value;
 	}
 
+	if (places == 0) {
+		return php_round_helper(value, mode);
+	}
+
 	places = places < INT_MIN+1 ? INT_MIN+1 : places;
 	precision_places = 14 - php_intlog10abs(value);
 
diff --git a/ext/standard/tests/math/round_gh12143_5.phpt b/ext/standard/tests/math/round_gh12143_5.phpt
new file mode 100644
index 0000000000000..9f05628e5de84
--- /dev/null
+++ b/ext/standard/tests/math/round_gh12143_5.phpt
@@ -0,0 +1,27 @@
+--TEST--
+GH-12143: Test rounding of 1.4999999999999998.
+--FILE--
+<?php
+foreach ([
+    1.4999999999999998,
+    -1.4999999999999998,
+] as $number) {
+    foreach ([
+        'PHP_ROUND_HALF_UP',
+        'PHP_ROUND_HALF_DOWN',
+        'PHP_ROUND_HALF_EVEN',
+        'PHP_ROUND_HALF_ODD',
+    ] as $mode) {
+        printf("%-20s: %+.17g -> %+.17g\n", $mode, $number, round($number, 0, constant($mode)));
+    }
+}
+?>
+--EXPECT--
+PHP_ROUND_HALF_UP   : +1.4999999999999998 -> +1
+PHP_ROUND_HALF_DOWN : +1.4999999999999998 -> +1
+PHP_ROUND_HALF_EVEN : +1.4999999999999998 -> +1
+PHP_ROUND_HALF_ODD  : +1.4999999999999998 -> +1
+PHP_ROUND_HALF_UP   : -1.4999999999999998 -> -1
+PHP_ROUND_HALF_DOWN : -1.4999999999999998 -> -1
+PHP_ROUND_HALF_EVEN : -1.4999999999999998 -> -1
+PHP_ROUND_HALF_ODD  : -1.4999999999999998 -> -1
diff --git a/ext/standard/tests/math/round_gh12143_6.phpt b/ext/standard/tests/math/round_gh12143_6.phpt
new file mode 100644
index 0000000000000..07b1cc73ce615
--- /dev/null
+++ b/ext/standard/tests/math/round_gh12143_6.phpt
@@ -0,0 +1,27 @@
+--TEST--
+GH-12143: Test rounding of 4503599627370495.5.
+--FILE--
+<?php
+foreach ([
+    4503599627370495.5,
+    -4503599627370495.5,
+] as $number) {
+    foreach ([
+        'PHP_ROUND_HALF_UP',
+        'PHP_ROUND_HALF_DOWN',
+        'PHP_ROUND_HALF_EVEN',
+        'PHP_ROUND_HALF_ODD',
+    ] as $mode) {
+        printf("%-20s: %+.17g -> %+.17g\n", $mode, $number, round($number, 0, constant($mode)));
+    }
+}
+?>
+--EXPECT--
+PHP_ROUND_HALF_UP   : +4503599627370495.5 -> +4503599627370496
+PHP_ROUND_HALF_DOWN : +4503599627370495.5 -> +4503599627370495
+PHP_ROUND_HALF_EVEN : +4503599627370495.5 -> +4503599627370496
+PHP_ROUND_HALF_ODD  : +4503599627370495.5 -> +4503599627370495
+PHP_ROUND_HALF_UP   : -4503599627370495.5 -> -4503599627370496
+PHP_ROUND_HALF_DOWN : -4503599627370495.5 -> -4503599627370495
+PHP_ROUND_HALF_EVEN : -4503599627370495.5 -> -4503599627370496
+PHP_ROUND_HALF_ODD  : -4503599627370495.5 -> -4503599627370495