From 1c1f006330bc972c59305444f33804714b18b23d Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Sat, 27 Apr 2024 14:40:38 +0200
Subject: [PATCH 01/11] Refactor some DateTime and TimeSpan formatting/parsing
 methods

---
 .../System/Globalization/DateTimeFormat.cs    |  8 ++--
 .../src/System/Globalization/DateTimeParse.cs |  1 +
 .../System/Globalization/TimeSpanFormat.cs    |  6 +--
 .../src/System/Globalization/TimeSpanParse.cs | 38 +++++++++++--------
 4 files changed, 30 insertions(+), 23 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
index 895a9e83b6a89d..3bc1298527f74e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
@@ -484,11 +484,11 @@ private static void FormatCustomized<TChar>(
                         tokenLen = ParseRepeatPattern(format, i, ch);
                         if (tokenLen <= MaxSecondsFractionDigits)
                         {
-                            long fraction = (dateTime.Ticks % Calendar.TicksPerSecond);
-                            fraction /= (long)Math.Pow(10, 7 - tokenLen);
+                            int fraction = (int)(dateTime.Ticks % Calendar.TicksPerSecond);
+                            fraction /= TimeSpanParse.Pow10(MaxSecondsFractionDigits - tokenLen);
                             if (ch == 'f')
                             {
-                                FormatFraction(ref result, (int)fraction, fixedNumberFormats[tokenLen - 1]);
+                                FormatFraction(ref result, fraction, fixedNumberFormats[tokenLen - 1]);
                             }
                             else
                             {
@@ -507,7 +507,7 @@ private static void FormatCustomized<TChar>(
                                 }
                                 if (effectiveDigits > 0)
                                 {
-                                    FormatFraction(ref result, (int)fraction, fixedNumberFormats[effectiveDigits - 1]);
+                                    FormatFraction(ref result, fraction, fixedNumberFormats[effectiveDigits - 1]);
                                 }
                                 else
                                 {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
index 687cafbe9ca500..1cf93ce07006c4 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
@@ -3179,6 +3179,7 @@ internal static bool ParseDigits(ref __DTString str, int minDigitLen, int maxDig
 
         private static bool ParseFractionExact(ref __DTString str, int maxDigitLen, scoped ref double result)
         {
+            Debug.Assert(maxDigitLen <= DateTimeFormat.MaxSecondsFractionDigits);
             if (!str.GetNextDigit())
             {
                 str.Index--;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
index 8c8bea12bbf6b2..e7f9f791694368 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
@@ -311,7 +311,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
             int seconds = (int)(time / TimeSpan.TicksPerSecond % 60);
             int fraction = (int)(time % TimeSpan.TicksPerSecond);
 
-            long tmp;
+            int tmp;
             int i = 0;
             int tokenLen;
 
@@ -357,7 +357,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
 
                         tmp = fraction;
                         tmp /= TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
-                        DateTimeFormat.FormatFraction(ref result, (int)tmp, DateTimeFormat.fixedNumberFormats[tokenLen - 1]);
+                        DateTimeFormat.FormatFraction(ref result, tmp, DateTimeFormat.fixedNumberFormats[tokenLen - 1]);
                         break;
                     case 'F':
                         //
@@ -386,7 +386,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
                         if (effectiveDigits > 0)
                         {
-                            DateTimeFormat.FormatFraction(ref result, (int)tmp, DateTimeFormat.fixedNumberFormats[effectiveDigits - 1]);
+                            DateTimeFormat.FormatFraction(ref result, tmp, DateTimeFormat.fixedNumberFormats[effectiveDigits - 1]);
                         }
                         break;
                     case 'd':
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index c900e64dcb9696..2cff1f046c7c9a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -47,7 +47,10 @@
 //
 ////////////////////////////////////////////////////////////////////////////
 
+using System.Buffers.Text;
 using System.Diagnostics;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using System.Text;
 
 namespace System.Globalization
@@ -114,7 +117,7 @@ public bool NormalizeAndValidateFraction()
                 if (_zeroes == 0 && _num > MaxFraction)
                     return false;
 
-                int totalDigitsCount = ((int)Math.Floor(Math.Log10(_num))) + 1 + _zeroes;
+                int totalDigitsCount = FormattingHelpers.CountDigits((uint)_num) + _zeroes;
 
                 if (totalDigitsCount == MaxFractionDigits)
                 {
@@ -132,7 +135,7 @@ public bool NormalizeAndValidateFraction()
                     // .000001  normalize to 10 ticks
                     // .1       normalize to 1,000,000 ticks
 
-                    _num *= (int)Pow10(MaxFractionDigits - totalDigitsCount);
+                    _num *= Pow10(MaxFractionDigits - totalDigitsCount);
                     return true;
                 }
 
@@ -143,7 +146,7 @@ public bool NormalizeAndValidateFraction()
                 // .099999999   normalize to 1,000,000 ticks
 
                 Debug.Assert(_zeroes > 0); // Already validated that in the condition _zeroes == 0 && _num > MaxFraction
-                _num = (int)Math.Round((double)_num / Pow10(totalDigitsCount - MaxFractionDigits), MidpointRounding.AwayFromZero);
+                _num = (int)Math.Round(_num / Math.Pow(10, totalDigitsCount - MaxFractionDigits), MidpointRounding.AwayFromZero);
                 Debug.Assert(_num < MaxFraction);
 
                 return true;
@@ -563,20 +566,23 @@ internal bool SetBadFormatSpecifierFailure(char? formatSpecifierCharacter = null
             }
         }
 
-        internal static long Pow10(int pow)
+        internal static int Pow10(int pow)
         {
-            return pow switch
-            {
-                0 => 1,
-                1 => 10,
-                2 => 100,
-                3 => 1000,
-                4 => 10000,
-                5 => 100000,
-                6 => 1000000,
-                7 => 10000000,
-                _ => (long)Math.Pow(10, pow),
-            };
+            Debug.Assert(pow > 0);
+            Debug.Assert(pow <= MaxFractionDigits);
+
+            ReadOnlySpan<int> powersOfTen = [
+                1,
+                10,
+                100,
+                1000,
+                10000,
+                100000,
+                1000000,
+                10000000,
+            ];
+            Debug.Assert(powersOfTen.Length == MaxFractionDigits + 1);
+            return Unsafe.Add(ref MemoryMarshal.GetReference(powersOfTen), pow);
         }
 
         private static bool TryTimeToTicks(bool positive, TimeSpanToken days, TimeSpanToken hours, TimeSpanToken minutes, TimeSpanToken seconds, TimeSpanToken fraction, out long result)

From 001ee0a0dd75fb553ed2b7ce7f80adf1b172a53a Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Sat, 27 Apr 2024 14:42:43 +0200
Subject: [PATCH 02/11] Fix assertion in TimeSpanParse.Pow10

---
 .../src/System/Globalization/TimeSpanParse.cs                  | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index 2cff1f046c7c9a..f1413c00ffa17a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -568,9 +568,8 @@ internal bool SetBadFormatSpecifierFailure(char? formatSpecifierCharacter = null
 
         internal static int Pow10(int pow)
         {
-            Debug.Assert(pow > 0);
+            Debug.Assert(pow >= 0);
             Debug.Assert(pow <= MaxFractionDigits);
-
             ReadOnlySpan<int> powersOfTen = [
                 1,
                 10,

From decf099d1eaf4a34146207b2a26047f44e78d664 Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Sat, 27 Apr 2024 15:25:11 +0200
Subject: [PATCH 03/11] Don't use Unsafe in TimeSpanParse.Pow10

---
 .../src/System/Globalization/TimeSpanParse.cs                 | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index f1413c00ffa17a..2f20b14c4f1468 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -49,8 +49,6 @@
 
 using System.Buffers.Text;
 using System.Diagnostics;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 using System.Text;
 
 namespace System.Globalization
@@ -581,7 +579,7 @@ internal static int Pow10(int pow)
                 10000000,
             ];
             Debug.Assert(powersOfTen.Length == MaxFractionDigits + 1);
-            return Unsafe.Add(ref MemoryMarshal.GetReference(powersOfTen), pow);
+            return powersOfTen[pow];
         }
 
         private static bool TryTimeToTicks(bool positive, TimeSpanToken days, TimeSpanToken hours, TimeSpanToken minutes, TimeSpanToken seconds, TimeSpanToken fraction, out long result)

From 267d5e861c022c338de5004bb6c85e26d6179039 Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Sat, 27 Apr 2024 15:34:51 +0200
Subject: [PATCH 04/11] Revert changes to TimeSpanParse.Pow10

---
 .../System/Globalization/DateTimeFormat.cs    |  2 +-
 .../System/Globalization/TimeSpanFormat.cs    |  4 +--
 .../src/System/Globalization/TimeSpanParse.cs | 30 +++++++++----------
 3 files changed, 17 insertions(+), 19 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
index 3bc1298527f74e..02ee787c5f21c1 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
@@ -485,7 +485,7 @@ private static void FormatCustomized<TChar>(
                         if (tokenLen <= MaxSecondsFractionDigits)
                         {
                             int fraction = (int)(dateTime.Ticks % Calendar.TicksPerSecond);
-                            fraction /= TimeSpanParse.Pow10(MaxSecondsFractionDigits - tokenLen);
+                            fraction /= (int)TimeSpanParse.Pow10(MaxSecondsFractionDigits - tokenLen);
                             if (ch == 'f')
                             {
                                 FormatFraction(ref result, fraction, fixedNumberFormats[tokenLen - 1]);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
index e7f9f791694368..6f468ce5a92f4f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
@@ -356,7 +356,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
 
                         tmp = fraction;
-                        tmp /= TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
+                        tmp /= (int)TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
                         DateTimeFormat.FormatFraction(ref result, tmp, DateTimeFormat.fixedNumberFormats[tokenLen - 1]);
                         break;
                     case 'F':
@@ -370,7 +370,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
 
                         tmp = fraction;
-                        tmp /= TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
+                        tmp /= (int)TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
                         int effectiveDigits = tokenLen;
                         while (effectiveDigits > 0)
                         {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index 2f20b14c4f1468..a48f423058fa4f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -133,7 +133,7 @@ public bool NormalizeAndValidateFraction()
                     // .000001  normalize to 10 ticks
                     // .1       normalize to 1,000,000 ticks
 
-                    _num *= Pow10(MaxFractionDigits - totalDigitsCount);
+                    _num *= (int)Pow10(MaxFractionDigits - totalDigitsCount);
                     return true;
                 }
 
@@ -564,22 +564,20 @@ internal bool SetBadFormatSpecifierFailure(char? formatSpecifierCharacter = null
             }
         }
 
-        internal static int Pow10(int pow)
+        internal static long Pow10(int pow)
         {
-            Debug.Assert(pow >= 0);
-            Debug.Assert(pow <= MaxFractionDigits);
-            ReadOnlySpan<int> powersOfTen = [
-                1,
-                10,
-                100,
-                1000,
-                10000,
-                100000,
-                1000000,
-                10000000,
-            ];
-            Debug.Assert(powersOfTen.Length == MaxFractionDigits + 1);
-            return powersOfTen[pow];
+            return pow switch
+            {
+                0 => 1,
+                1 => 10,
+                2 => 100,
+                3 => 1000,
+                4 => 10000,
+                5 => 100000,
+                6 => 1000000,
+                7 => 10000000,
+                _ => (long)Math.Pow(10, pow),
+            };
         }
 
         private static bool TryTimeToTicks(bool positive, TimeSpanToken days, TimeSpanToken hours, TimeSpanToken minutes, TimeSpanToken seconds, TimeSpanToken fraction, out long result)

From 61863e304562402b41e9b19bd35222700956473b Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Sat, 27 Apr 2024 16:04:14 +0200
Subject: [PATCH 05/11] Revert "Revert changes to TimeSpanParse.Pow10"

This reverts commit 267d5e861c022c338de5004bb6c85e26d6179039.
---
 .../System/Globalization/DateTimeFormat.cs    |  2 +-
 .../System/Globalization/TimeSpanFormat.cs    |  4 +--
 .../src/System/Globalization/TimeSpanParse.cs | 30 ++++++++++---------
 3 files changed, 19 insertions(+), 17 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
index 02ee787c5f21c1..3bc1298527f74e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
@@ -485,7 +485,7 @@ private static void FormatCustomized<TChar>(
                         if (tokenLen <= MaxSecondsFractionDigits)
                         {
                             int fraction = (int)(dateTime.Ticks % Calendar.TicksPerSecond);
-                            fraction /= (int)TimeSpanParse.Pow10(MaxSecondsFractionDigits - tokenLen);
+                            fraction /= TimeSpanParse.Pow10(MaxSecondsFractionDigits - tokenLen);
                             if (ch == 'f')
                             {
                                 FormatFraction(ref result, fraction, fixedNumberFormats[tokenLen - 1]);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
index 6f468ce5a92f4f..e7f9f791694368 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
@@ -356,7 +356,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
 
                         tmp = fraction;
-                        tmp /= (int)TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
+                        tmp /= TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
                         DateTimeFormat.FormatFraction(ref result, tmp, DateTimeFormat.fixedNumberFormats[tokenLen - 1]);
                         break;
                     case 'F':
@@ -370,7 +370,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
 
                         tmp = fraction;
-                        tmp /= (int)TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
+                        tmp /= TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
                         int effectiveDigits = tokenLen;
                         while (effectiveDigits > 0)
                         {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index a48f423058fa4f..2f20b14c4f1468 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -133,7 +133,7 @@ public bool NormalizeAndValidateFraction()
                     // .000001  normalize to 10 ticks
                     // .1       normalize to 1,000,000 ticks
 
-                    _num *= (int)Pow10(MaxFractionDigits - totalDigitsCount);
+                    _num *= Pow10(MaxFractionDigits - totalDigitsCount);
                     return true;
                 }
 
@@ -564,20 +564,22 @@ internal bool SetBadFormatSpecifierFailure(char? formatSpecifierCharacter = null
             }
         }
 
-        internal static long Pow10(int pow)
+        internal static int Pow10(int pow)
         {
-            return pow switch
-            {
-                0 => 1,
-                1 => 10,
-                2 => 100,
-                3 => 1000,
-                4 => 10000,
-                5 => 100000,
-                6 => 1000000,
-                7 => 10000000,
-                _ => (long)Math.Pow(10, pow),
-            };
+            Debug.Assert(pow >= 0);
+            Debug.Assert(pow <= MaxFractionDigits);
+            ReadOnlySpan<int> powersOfTen = [
+                1,
+                10,
+                100,
+                1000,
+                10000,
+                100000,
+                1000000,
+                10000000,
+            ];
+            Debug.Assert(powersOfTen.Length == MaxFractionDigits + 1);
+            return powersOfTen[pow];
         }
 
         private static bool TryTimeToTicks(bool positive, TimeSpanToken days, TimeSpanToken hours, TimeSpanToken minutes, TimeSpanToken seconds, TimeSpanToken fraction, out long result)

From 95857be015688fbbe498b5fb7db24010f125cf74 Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Sat, 27 Apr 2024 20:42:37 +0200
Subject: [PATCH 06/11] Change method name to Pow10UpToMaxFractionDigits

---
 .../src/System/Globalization/DateTimeFormat.cs              | 2 +-
 .../src/System/Globalization/DateTimeParse.cs               | 2 +-
 .../src/System/Globalization/TimeSpanFormat.cs              | 4 ++--
 .../src/System/Globalization/TimeSpanParse.cs               | 6 ++----
 4 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
index 3bc1298527f74e..db12f89bf2dd18 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
@@ -485,7 +485,7 @@ private static void FormatCustomized<TChar>(
                         if (tokenLen <= MaxSecondsFractionDigits)
                         {
                             int fraction = (int)(dateTime.Ticks % Calendar.TicksPerSecond);
-                            fraction /= TimeSpanParse.Pow10(MaxSecondsFractionDigits - tokenLen);
+                            fraction /= TimeSpanParse.Pow10UpToMaxFractionDigits(MaxSecondsFractionDigits - tokenLen);
                             if (ch == 'f')
                             {
                                 FormatFraction(ref result, fraction, fixedNumberFormats[tokenLen - 1]);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
index 1cf93ce07006c4..9613bddf435490 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
@@ -3198,7 +3198,7 @@ private static bool ParseFractionExact(ref __DTString str, int maxDigitLen, scop
                 result = result * 10 + str.GetDigit();
             }
 
-            result /= TimeSpanParse.Pow10(digitLen);
+            result /= TimeSpanParse.Pow10UpToMaxFractionDigits(digitLen);
             return digitLen == maxDigitLen;
         }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
index e7f9f791694368..48faa5b1a98345 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
@@ -356,7 +356,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
 
                         tmp = fraction;
-                        tmp /= TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
+                        tmp /= TimeSpanParse.Pow10UpToMaxFractionDigits(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
                         DateTimeFormat.FormatFraction(ref result, tmp, DateTimeFormat.fixedNumberFormats[tokenLen - 1]);
                         break;
                     case 'F':
@@ -370,7 +370,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
 
                         tmp = fraction;
-                        tmp /= TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
+                        tmp /= TimeSpanParse.Pow10UpToMaxFractionDigits(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
                         int effectiveDigits = tokenLen;
                         while (effectiveDigits > 0)
                         {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index 2f20b14c4f1468..6e256815a77074 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -133,7 +133,7 @@ public bool NormalizeAndValidateFraction()
                     // .000001  normalize to 10 ticks
                     // .1       normalize to 1,000,000 ticks
 
-                    _num *= Pow10(MaxFractionDigits - totalDigitsCount);
+                    _num *= Pow10UpToMaxFractionDigits(MaxFractionDigits - totalDigitsCount);
                     return true;
                 }
 
@@ -564,10 +564,8 @@ internal bool SetBadFormatSpecifierFailure(char? formatSpecifierCharacter = null
             }
         }
 
-        internal static int Pow10(int pow)
+        internal static int Pow10UpToMaxFractionDigits(int pow)
         {
-            Debug.Assert(pow >= 0);
-            Debug.Assert(pow <= MaxFractionDigits);
             ReadOnlySpan<int> powersOfTen = [
                 1,
                 10,

From 2fe27c1536c06e5ec001f030a67ed6cbbdd2f032 Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Sun, 28 Apr 2024 12:15:54 +0200
Subject: [PATCH 07/11] Fix
 TimeSpanParse.TimeSpanToken.NormalizeAndValidateFraction

---
 .../src/System/Globalization/TimeSpanParse.cs        | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index 6e256815a77074..99632b6cb10bb2 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -144,7 +144,17 @@ public bool NormalizeAndValidateFraction()
                 // .099999999   normalize to 1,000,000 ticks
 
                 Debug.Assert(_zeroes > 0); // Already validated that in the condition _zeroes == 0 && _num > MaxFraction
-                _num = (int)Math.Round(_num / Math.Pow(10, totalDigitsCount - MaxFractionDigits), MidpointRounding.AwayFromZero);
+
+                if (_zeroes > MaxFractionDigits)
+                {
+                    // If there are 8 leading zeroes, it rounds to zero
+                    _num = 0;
+                    return true;
+                }
+
+                Debug.Assert(totalDigitsCount - MaxFractionDigits <= MaxFractionDigits);
+                uint power = (uint)Pow10UpToMaxFractionDigits(totalDigitsCount - MaxFractionDigits);
+                _num = (int)(((uint)_num + power / 2) / power);
                 Debug.Assert(_num < MaxFraction);
 
                 return true;

From dd64b4259ffbde4ed806ba1767a87dfcb8ea9e2e Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Thu, 2 May 2024 15:36:51 +0200
Subject: [PATCH 08/11] Address feedback in TimeSpanParse

---
 .../src/System/Globalization/TimeSpanParse.cs               | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index 99632b6cb10bb2..40c114ba7a9c3f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -153,8 +153,7 @@ public bool NormalizeAndValidateFraction()
                 }
 
                 Debug.Assert(totalDigitsCount - MaxFractionDigits <= MaxFractionDigits);
-                uint power = (uint)Pow10UpToMaxFractionDigits(totalDigitsCount - MaxFractionDigits);
-                _num = (int)(((uint)_num + power / 2) / power);
+                _num = (int)Math.Round((double)_num / Pow10UpToMaxFractionDigits(totalDigitsCount - MaxFractionDigits), MidpointRounding.AwayFromZero);
                 Debug.Assert(_num < MaxFraction);
 
                 return true;
@@ -576,7 +575,8 @@ internal bool SetBadFormatSpecifierFailure(char? formatSpecifierCharacter = null
 
         internal static int Pow10UpToMaxFractionDigits(int pow)
         {
-            ReadOnlySpan<int> powersOfTen = [
+            ReadOnlySpan<int> powersOfTen =
+            [
                 1,
                 10,
                 100,

From 0c04b2ff4afa68578339fe2bb5ae9a4a22483eaf Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Fri, 3 May 2024 10:51:21 +0200
Subject: [PATCH 09/11] Change from Math.Round to uint divison in
 TimeSpanParse.NormalizeAndValidateFraction

---
 .../src/System/Globalization/TimeSpanParse.cs                  | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index 40c114ba7a9c3f..b41b8d1b01fdf8 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -153,7 +153,8 @@ public bool NormalizeAndValidateFraction()
                 }
 
                 Debug.Assert(totalDigitsCount - MaxFractionDigits <= MaxFractionDigits);
-                _num = (int)Math.Round((double)_num / Pow10UpToMaxFractionDigits(totalDigitsCount - MaxFractionDigits), MidpointRounding.AwayFromZero);
+                uint power = (uint)Pow10UpToMaxFractionDigits(totalDigitsCount - MaxFractionDigits);
+                _num = (int)(((uint)_num + power / 2) / power);
                 Debug.Assert(_num < MaxFraction);
 
                 return true;

From e45515014f478cddd01e9097e204e733eb85ec4a Mon Sep 17 00:00:00 2001
From: lilinus <linus.hamlin@outlook.com>
Date: Sun, 5 May 2024 12:00:07 +0200
Subject: [PATCH 10/11] Comment for rounding division in
 TimeSpanParse.NormalizeAndValidateFraction

---
 .../src/System/Globalization/TimeSpanParse.cs                   | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index b41b8d1b01fdf8..3d5a2570d3c21f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -154,7 +154,7 @@ public bool NormalizeAndValidateFraction()
 
                 Debug.Assert(totalDigitsCount - MaxFractionDigits <= MaxFractionDigits);
                 uint power = (uint)Pow10UpToMaxFractionDigits(totalDigitsCount - MaxFractionDigits);
-                _num = (int)(((uint)_num + power / 2) / power);
+                _num = (int)(((uint)_num + power / 2) / power); // Rounding integer divsion, (midpint rounds up).
                 Debug.Assert(_num < MaxFraction);
 
                 return true;

From ef86e5a392bd1cd466f24451c811b744f5cd617a Mon Sep 17 00:00:00 2001
From: Linus Hamlin <78953007+lilinus@users.noreply.github.com>
Date: Sun, 5 May 2024 22:35:51 +0200
Subject: [PATCH 11/11] Update
 src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs

Co-authored-by: xtqqczze <45661989+xtqqczze@users.noreply.github.com>
---
 .../src/System/Globalization/TimeSpanParse.cs                  | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index 3d5a2570d3c21f..033d0abe4e9049 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -154,7 +154,8 @@ public bool NormalizeAndValidateFraction()
 
                 Debug.Assert(totalDigitsCount - MaxFractionDigits <= MaxFractionDigits);
                 uint power = (uint)Pow10UpToMaxFractionDigits(totalDigitsCount - MaxFractionDigits);
-                _num = (int)(((uint)_num + power / 2) / power); // Rounding integer divsion, (midpint rounds up).
+                // Unsigned integer division, rounding away from zero
+                _num = (int)(((uint)_num + power / 2) / power);
                 Debug.Assert(_num < MaxFraction);
 
                 return true;