Update pure python float checking.

Our C++ strtod was updated to handle text-format rounding about a month after it was ported to python.

PiperOrigin-RevId: 706000143

Author: mkruskal-google

conformance/text_format_failure_list_python.txt

@@ -7,12 +7,3 @@ Required.*.TextFormatInput.StringLiteralBasicEscapesBytes.ProtobufOutput
 Required.*.TextFormatInput.StringLiteralBasicEscapesBytes.TextFormatOutput                                         # Output was not equivalent to reference message: modified: optional_bytes: "\007\010\014\n\r\t\013?\\\'\"" -> "\007\010\014\n\r\t
 Required.*.TextFormatInput.StringLiteralBasicEscapesString.ProtobufOutput                                          # Output was not equivalent to reference message: modified: optional_string: "\007\010\014\n\r\t\013?\\\'\"" -> "\007\010\014\n\r\
 Required.*.TextFormatInput.StringLiteralBasicEscapesString.TextFormatOutput                                        # Output was not equivalent to reference message: modified: optional_string: "\007\010\014\n\r\t\013?\\\'\"" -> "\007\010\014\n\r\
-
-# Optional float interpreted as `inf`
-Required.*.TextFormatInput.FloatFieldMaxValue.ProtobufOutput                                                       # Output was not equivalent to reference message
-Required.*.TextFormatInput.FloatFieldMaxValue.TextFormatOutput                                                     # Output was not equivalent to reference message
-Required.*.TextFormatInput.FloatFieldMaxValue_f.ProtobufOutput                                                     # Output was not equivalent to reference message
-Required.*.TextFormatInput.FloatFieldMaxValue_f.TextFormatOutput                                                   # Output was not equivalent to reference message
-Required.*.TextFormatInput.FloatFieldMaxValue_F.ProtobufOutput                                                     # Output was not equivalent to reference message
-Required.*.TextFormatInput.FloatFieldMaxValue_F.TextFormatOutput                                                   # Output was not equivalent to reference message
-

python/google/protobuf/internal/type_checkers.py

@@ -231,6 +231,7 @@ class Uint64ValueChecker(IntValueChecker):
 # The max 4 bytes float is about 3.4028234663852886e+38
 _FLOAT_MAX = float.fromhex('0x1.fffffep+127')
 _FLOAT_MIN = -_FLOAT_MAX
+_MAX_FLOAT_AS_DOUBLE_ROUNDED = 3.4028235677973366e38
 _INF = float('inf')
 _NEG_INF = float('-inf')
 
@@ -269,8 +270,12 @@ def CheckValue(self, proposed_value):
     converted_value = super().CheckValue(proposed_value)
     # This inf rounding matches the C++ proto SafeDoubleToFloat logic.
     if converted_value > _FLOAT_MAX:
+      if converted_value <= _MAX_FLOAT_AS_DOUBLE_ROUNDED:
+        return _FLOAT_MAX
       return _INF
     if converted_value < _FLOAT_MIN:
+      if converted_value >= -_MAX_FLOAT_AS_DOUBLE_ROUNDED:
+        return _FLOAT_MIN
       return _NEG_INF
 
     return TruncateToFourByteFloat(converted_value)