Add overflow check. Limit each individual section to 32-bit signed

Author: Morten Haraldsen

src/main/java/com/ethlo/time/ItuDurationParser.java

@@ -94,7 +94,15 @@ private static int readUntilNonDigit(final String chars, final int offset, final
             }
             else
             {
-                value = value * RADIX + (c - ZERO);
+                int digit = c - ZERO;
+
+                // Correct overflow check
+                if (value > 214748364 || (value == 214748364 && digit > 7))
+                {
+                    throw new DateTimeParseException("Numeric overflow while parsing value", chars, idx);
+                }
+
+                value = value * RADIX + digit;
                 idx++;
             }
         }
@@ -198,6 +206,12 @@ public final void accept(final String chars, final int index, final int length,
                 throw new DateTimeParseException("Duration must start with 'P'", chars, 0);
             }
 
+            /*
+             * An int can never overflow a long when used for seconds, minutes, hours, days, and weeks,
+             * even at their maximum values, because the total number of seconds remains within the
+             * 64-bit long's limits.
+             */
+
             switch (unit)
             {
                 case 'T':
@@ -248,7 +262,7 @@ public final void accept(final String chars, final int index, final int length,
                         int remainingDigits = DIGITS_IN_NANO - length;
                         if (remainingDigits > 0)
                         {
-                            nano *= POW10_TABLE[remainingDigits]; // Use lookup instead of loop
+                            nano *= POW10_TABLE[remainingDigits];
                         }
                         readingFractionalPart = false;
                     }

src/test/java/com/ethlo/time/ItuDurationParserTest.java

@@ -56,7 +56,6 @@ void testValidFullNotNormalizedToNormalized()
     @Test
     void shouldParseZeroDuration()
     {
-        // Input: P0D (zero duration)
         Duration duration = ItuDurationParser.parse("P0D").toDuration();
         assertThat(duration).isEqualTo(Duration.ZERO);
     }
@@ -77,6 +76,15 @@ void shouldParseDurationWithNoTimeSection()
         assertThat(duration).isEqualTo(Duration.ofDays(30));
     }
 
+    @Test
+    void shouldThrowDateTimeParseExceptionForOverflow()
+    {
+        final String input = "P999999999999D";
+        assertThatThrownBy(() -> ItuDurationParser.parse(input))
+                .isInstanceOf(DateTimeParseException.class)
+                .hasMessageContaining("Numeric overflow while parsing value");
+    }
+
     @Test
     void shouldThrowDateTimeParseExceptionForInvalidUnits()
     {