Revert changes to TimeSpanParse.Pow10

Author: lilinus

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]);

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)
                         {

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)