[release/6.0-preview2] Track trailing zeros only for floating point numbers (#48857)

* Track trailing zeros only for floating point numbers

* Undo previous unit test change

* Add a roundtrip unit test

* Move check outside the loop

* Globalization

* Also fix #48648 and unit tests

* Assert and unit test

Co-authored-by: Prashanth Govindarajan <prgovi@microsoft.com>

7 files changed, 53 insertions, 15 deletions

diff --git a/src/libraries/System.Formats.Cbor/tests/Writer/CborWriterTests.Tag.cs b/src/libraries/System.Formats.Cbor/tests/Writer/CborWriterTests.Tag.cs
index 88cb2f0ee95..b9cc53ceb23 100644
--- a/src/libraries/System.Formats.Cbor/tests/Writer/CborWriterTests.Tag.cs
+++ b/src/libraries/System.Formats.Cbor/tests/Writer/CborWriterTests.Tag.cs
@@ -158,7 +158,7 @@ namespace System.Formats.Cbor.Tests
         [InlineData("1", "c4820001")]
         [InlineData("-1", "c4820020")]
         [InlineData("1.1", "c482200b")]
-        [InlineData("1.000", "c4820001")]
+        [InlineData("1.000", "c482221903e8")]
         [InlineData("273.15", "c48221196ab3")]
         [InlineData("79228162514264337593543950335", "c48200c24cffffffffffffffffffffffff")] // decimal.MaxValue
         [InlineData("7922816251426433759354395033.5", "c48220c24cffffffffffffffffffffffff")]
diff --git a/src/libraries/System.Private.CoreLib/src/System/Number.Parsing.cs b/src/libraries/System.Private.CoreLib/src/System/Number.Parsing.cs
index a07153cad25..382eb1ccf82 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Number.Parsing.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Number.Parsing.cs
@@ -358,9 +358,10 @@ namespace System
                         {
                             number.Scale++;
                         }
-                        else if (digCount < maxDigCount)
+
+                        if (digCount < maxDigCount)
                         {
-                            // Handle a case like "53.0". We need to ignore trailing zeros in the fractional part, so we keep a count of the number of trailing zeros and update digCount later
+                            // Handle a case like "53.0". We need to ignore trailing zeros in the fractional part for floating point numbers, so we keep a count of the number of trailing zeros and update digCount later
                             if (ch == '0')
                             {
                                 numberOfTrailingZeros++;
@@ -395,17 +396,8 @@ namespace System
             }
 
             bool negExp = false;
-            if (digEnd == maxDigCount && numberOfTrailingZeros > 0 && number.HasNonZeroTail)
-            {
-                // We have a non-zero digit in the input past maxDigitCount. We already handle this properly.
-                number.DigitsCount = digEnd;
-            }
-            else
-            {
-                // We have trailing 0s in the fractional part. We can strip it all out
-                number.DigitsCount = digEnd - numberOfTrailingZeros;
-            }
-            number.Digits[number.DigitsCount] = (byte)('\0');
+            number.DigitsCount = digEnd;
+            number.Digits[digEnd] = (byte)('\0');
             if ((state & StateDigits) != 0)
             {
                 if ((ch == 'E' || ch == 'e') && ((styles & NumberStyles.AllowExponent) != 0))
@@ -449,6 +441,20 @@ namespace System
                         ch = p < strEnd ? *p : '\0';
                     }
                 }
+
+                if (number.Kind == NumberBufferKind.FloatingPoint && !number.HasNonZeroTail)
+                {
+                    // Adjust the number buffer for trailing zeros
+                    int numberOfFractionalDigits = digEnd - number.Scale;
+                    if (numberOfFractionalDigits > 0)
+                    {
+                        numberOfTrailingZeros = Math.Min(numberOfTrailingZeros, numberOfFractionalDigits);
+                        Debug.Assert(numberOfTrailingZeros >= 0);
+                        number.DigitsCount = digEnd - numberOfTrailingZeros;
+                        number.Digits[number.DigitsCount] = (byte)('\0');
+                    }
+                }
+
                 while (true)
                 {
                     if (!IsWhite(ch) || (styles & NumberStyles.AllowTrailingWhite) == 0)
@@ -2025,7 +2031,7 @@ namespace System
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static unsafe char* MatchNegativeSignChars(char* p, char* pEnd, NumberFormatInfo info)
         {
-            char *ret = MatchChars(p, pEnd, info.NegativeSign);
+            char* ret = MatchChars(p, pEnd, info.NegativeSign);
             if (ret == null && info.AllowHyphenDuringParsing && p < pEnd && *p == '-')
             {
                 ret = p + 1;
diff --git a/src/libraries/System.Runtime/tests/System/DecimalTests.cs b/src/libraries/System.Runtime/tests/System/DecimalTests.cs
index e4f3c9d8012..35069a81e61 100644
--- a/src/libraries/System.Runtime/tests/System/DecimalTests.cs
+++ b/src/libraries/System.Runtime/tests/System/DecimalTests.cs
@@ -1500,6 +1500,14 @@ namespace System.Tests
             Assert.Throws<FormatException>(() => f.ToString("E" + intMaxPlus1String));
         }
 
+        [Theory]
+        [InlineData("3.00")]
+        public void TestRoundTripDecimalToString(string input)
+        {
+            decimal d = Decimal.Parse(input, NumberStyles.Number, NumberFormatInfo.InvariantInfo);
+            string dString = d.ToString(CultureInfo.InvariantCulture);
+            Assert.Equal(input, dString);
+        }
         public static IEnumerable<object[]> Truncate_TestData()
         {
             yield return new object[] { 123m, 123m };
diff --git a/src/libraries/System.Runtime/tests/System/DoubleTests.cs b/src/libraries/System.Runtime/tests/System/DoubleTests.cs
index 8403fe131d6..d0bfcfb4141 100644
--- a/src/libraries/System.Runtime/tests/System/DoubleTests.cs
+++ b/src/libraries/System.Runtime/tests/System/DoubleTests.cs
@@ -290,6 +290,13 @@ namespace System.Tests
             yield return new object[] { "0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", defaultStyle, invariantFormat, 0.0 };
             yield return new object[] { "0.005", defaultStyle, invariantFormat, 0.005 };
             yield return new object[] { "0.0500", defaultStyle, invariantFormat, 0.05 };
+            yield return new object[] { "6250000000000000000000000000000000e-12", defaultStyle, invariantFormat, 6.25e21 };
+            yield return new object[] { "6250000e0", defaultStyle, invariantFormat, 6.25e6 };
+            yield return new object[] { "6250100e-5", defaultStyle, invariantFormat, 62.501 };
+            yield return new object[] { "625010.00e-4", defaultStyle, invariantFormat, 62.501 };
+            yield return new object[] { "62500e-4", defaultStyle, invariantFormat, 6.25 };
+            yield return new object[] { "62500", defaultStyle, invariantFormat, 62500.0 };
+            yield return new object[] { "10e-3", defaultStyle, invariantFormat, 0.01 };
 
             yield return new object[] { (123.1).ToString(), NumberStyles.AllowDecimalPoint, null, 123.1 };
             yield return new object[] { (1000.0).ToString("N0"), NumberStyles.AllowThousands, null, 1000.0 };
diff --git a/src/libraries/System.Runtime/tests/System/HalfTests.cs b/src/libraries/System.Runtime/tests/System/HalfTests.cs
index e851f28815f..926034b5b70 100644
--- a/src/libraries/System.Runtime/tests/System/HalfTests.cs
+++ b/src/libraries/System.Runtime/tests/System/HalfTests.cs
@@ -685,6 +685,11 @@ namespace System.Tests
             yield return new object[] { "0.000000000000000000", defaultStyle, invariantFormat, 0.0f };
             yield return new object[] { "0.005", defaultStyle, invariantFormat, 0.005f };
             yield return new object[] { "0.0400", defaultStyle, invariantFormat, 0.04f };
+            yield return new object[] { "1200e0", defaultStyle, invariantFormat, 1200.0f };
+            yield return new object[] { "120100e-4", defaultStyle, invariantFormat, 12.01f };
+            yield return new object[] { "12010.00e-4", defaultStyle, invariantFormat, 1.201f };
+            yield return new object[] { "12000e-4", defaultStyle, invariantFormat, 1.2f };
+            yield return new object[] { "1200", defaultStyle, invariantFormat, 1200.0f };
 
             yield return new object[] { (123.1f).ToString(), NumberStyles.AllowDecimalPoint, null, 123.1f };
             yield return new object[] { (1000.0f).ToString("N0"), NumberStyles.AllowThousands, null, 1000.0f };
diff --git a/src/libraries/System.Runtime/tests/System/Int32Tests.cs b/src/libraries/System.Runtime/tests/System/Int32Tests.cs
index f64df4bcc31..fca800ca292 100644
--- a/src/libraries/System.Runtime/tests/System/Int32Tests.cs
+++ b/src/libraries/System.Runtime/tests/System/Int32Tests.cs
@@ -355,6 +355,12 @@ namespace System.Tests
             yield return new object[] { "123123", NumberStyles.AllowLeadingSign, new NumberFormatInfo() { NegativeSign = "123" }, -123 };
             yield return new object[] { "123123", NumberStyles.AllowLeadingSign, new NumberFormatInfo() { PositiveSign = "12312" }, 3 };
             yield return new object[] { "123123", NumberStyles.AllowLeadingSign, new NumberFormatInfo() { NegativeSign = "12312" }, -3 };
+
+            // Test trailing zeros
+            yield return new object[] { "3.00", NumberStyles.Number, CultureInfo.InvariantCulture, 3 };
+            yield return new object[] { "3.00000000", NumberStyles.Number, CultureInfo.InvariantCulture, 3 };
+            yield return new object[] { "3.000000000", NumberStyles.Number, CultureInfo.InvariantCulture, 3 };
+            yield return new object[] { "3.0000000000", NumberStyles.Number, CultureInfo.InvariantCulture, 3 };
         }
 
         [Theory]
diff --git a/src/libraries/System.Runtime/tests/System/SingleTests.cs b/src/libraries/System.Runtime/tests/System/SingleTests.cs
index 1fa4916c172..962621d05c1 100644
--- a/src/libraries/System.Runtime/tests/System/SingleTests.cs
+++ b/src/libraries/System.Runtime/tests/System/SingleTests.cs
@@ -295,6 +295,12 @@ namespace System.Tests
             yield return new object[] { "0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", defaultStyle, invariantFormat, 0.0f };
             yield return new object[] { "0.005", defaultStyle, invariantFormat, 0.005f };
             yield return new object[] { "0.0500", defaultStyle, invariantFormat, 0.05f };
+            yield return new object[] { "6250000000000000000000000000000000e-12", defaultStyle, invariantFormat, 6.25e21f };
+            yield return new object[] { "6250000e0", defaultStyle, invariantFormat, 6.25e6f };
+            yield return new object[] { "6250100e-5", defaultStyle, invariantFormat, 62.501f };
+            yield return new object[] { "625010.00e-4", defaultStyle, invariantFormat, 62.501f };
+            yield return new object[] { "62500e-4", defaultStyle, invariantFormat, 6.25f };
+            yield return new object[] { "62500", defaultStyle, invariantFormat, 62500.0f };
 
             yield return new object[] { (123.1f).ToString(), NumberStyles.AllowDecimalPoint, null, 123.1f };
             yield return new object[] { (1000.0f).ToString("N0"), NumberStyles.AllowThousands, null, 1000.0f };