[3.6] bpo-31373: remove overly strict float range checks (GH-3486) (#3495)

This undoes a853a8ba7850381d49b284295dd6f0dc491dbe44 except for the pytime.c
parts. We want to continue to allow IEEE 754 doubles larger than FLT_MAX to be
rounded into finite floats. Tests were added to very this behavior.
(cherry picked from commit 2bb69a5b4e7f96cb35d1b28aa7b7b3974b351f59)

2 files changed, 12 insertions, 0 deletions

diff --git a/Lib/test/test_float.py b/Lib/test/test_float.py
index 6491f45..c5ca50c 100644
--- a/Lib/test/test_float.py
+++ b/Lib/test/test_float.py
@@ -613,6 +613,12 @@ class IEEEFormatTestCase(unittest.TestCase):
                           ('<f', LE_FLOAT_NAN)]:
             struct.unpack(fmt, data)
 
+    @support.requires_IEEE_754
+    def test_serialized_float_rounding(self):
+        from _testcapi import FLT_MAX
+        self.assertEqual(struct.pack("<f", 3.40282356e38), struct.pack("<f", FLT_MAX))
+        self.assertEqual(struct.pack("<f", -3.40282356e38), struct.pack("<f", -FLT_MAX))
+
 class FormatTestCase(unittest.TestCase):
 
     def test_format(self):
diff --git a/Lib/test/test_getargs2.py b/Lib/test/test_getargs2.py
index 8a194aa..d14a6ee 100644
--- a/Lib/test/test_getargs2.py
+++ b/Lib/test/test_getargs2.py
@@ -377,6 +377,12 @@ class Float_TestCase(unittest.TestCase):
         r = getargs_f(NAN)
         self.assertNotEqual(r, r)
 
+    @support.requires_IEEE_754
+    def test_f_rounding(self):
+        from _testcapi import getargs_f
+        self.assertEqual(getargs_f(3.40282356e38), FLT_MAX)
+        self.assertEqual(getargs_f(-3.40282356e38), -FLT_MAX)
+
     def test_d(self):
         from _testcapi import getargs_d
         self.assertEqual(getargs_d(4.25), 4.25)