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[release/7.0] Fix FormattingHelpers.CountDigits(UInt128) and add more tests for Int128/UInt128.ToString #74536

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Aug 25, 2022
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[release/7.0] Fix FormattingHelpers.CountDigits(UInt128) and add more tests for Int128/UInt128.ToString #74536

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23 changes: 19 additions & 4 deletions ...libraries/System.Private.CoreLib/src/System/Buffers/Text/FormattingHelpers.CountDigits.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,22 +14,37 @@ public static int CountDigits(UInt128 value)
{
ulong upper = value.Upper;

if (upper < 5)
// 1e19 is 8AC7_2304_89E8_0000
// 1e20 is 5_6BC7_5E2D_6310_0000
// 1e21 is 36_35C9_ADC5_DEA0_0000

if (upper == 0)
{
// We have less than 64-bits, so just return the lower count
return CountDigits(value.Lower);
}

int digits = 19;
// We have more than 1e19, so we have at least 20 digits
int digits = 20;

if (upper > 5)
{
digits++;
// ((2^128) - 1) / 1e20 < 34_02_823_669_209_384_635 which
// is 18.5318 digits, meaning the result definitely fits
// into 64-bits and we only need to add the lower digit count

value /= new UInt128(0x5, 0x6BC7_5E2D_6310_0000); // value /= 1e20
Debug.Assert(value.Upper == 0);

digits += CountDigits(value.Lower);
}
else if (value.Lower >= 0x6BC75E2D63100000)
else if ((upper == 5) && (value.Lower >= 0x6BC75E2D63100000))
{
// We're greater than 1e20, but definitely less than 1e21
// so we have exactly 21 digits

digits++;
Debug.Assert(digits == 21);
}

return digits;
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6 changes: 6 additions & 0 deletions src/libraries/System.Runtime/tests/System/Int128Tests.cs
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Expand Up @@ -116,6 +116,12 @@ public static IEnumerable<object[]> ToString_TestData()
yield return new object[] { (Int128)(-4567), defaultSpecifier, defaultFormat, "-4567" };
yield return new object[] { (Int128)0, defaultSpecifier, defaultFormat, "0" };
yield return new object[] { (Int128)4567, defaultSpecifier, defaultFormat, "4567" };
yield return new object[] { new Int128(0x0000_0000_0000_0001, 0x0000_0000_0000_0003), defaultSpecifier, defaultFormat, "18446744073709551619" };
yield return new object[] { new Int128(0x0000_0000_0000_0001, 0x0000_0000_0000_000A), defaultSpecifier, defaultFormat, "18446744073709551626" };
yield return new object[] { new Int128(0x0000_0000_0000_0005, 0x0000_0000_0000_0001), defaultSpecifier, defaultFormat, "92233720368547758081" };
yield return new object[] { new Int128(0x0000_0000_0000_0005, 0x6BC7_5E2D_6310_0000), defaultSpecifier, defaultFormat, "100000000000000000000" };
yield return new object[] { new Int128(0x0000_0000_0000_0036, 0x35C9_ADC5_DEA0_0000), defaultSpecifier, defaultFormat, "1000000000000000000000" };
yield return new object[] { new Int128(0x0013_4261_72C7_4D82, 0x2B87_8FE8_0000_0000), defaultSpecifier, defaultFormat, "100000000000000000000000000000000000" };
yield return new object[] { Int128.MaxValue, defaultSpecifier, defaultFormat, "170141183460469231731687303715884105727" };
}

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8 changes: 8 additions & 0 deletions src/libraries/System.Runtime/tests/System/UInt128Tests.cs
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Expand Up @@ -101,6 +101,14 @@ public static IEnumerable<object[]> ToString_TestData()
{
yield return new object[] { (UInt128)0, defaultSpecifier, defaultFormat, "0" };
yield return new object[] { (UInt128)4567, defaultSpecifier, defaultFormat, "4567" };
yield return new object[] { new UInt128(0x0000_0000_0000_0001, 0x0000_0000_0000_0003), defaultSpecifier, defaultFormat, "18446744073709551619" };
yield return new object[] { new UInt128(0x0000_0000_0000_0001, 0x0000_0000_0000_000A), defaultSpecifier, defaultFormat, "18446744073709551626" };
yield return new object[] { new UInt128(0x0000_0000_0000_0005, 0x0000_0000_0000_0001), defaultSpecifier, defaultFormat, "92233720368547758081" };
yield return new object[] { new UInt128(0x0000_0000_0000_0005, 0x6BC7_5E2D_6310_0000), defaultSpecifier, defaultFormat, "100000000000000000000" };
yield return new object[] { new UInt128(0x0000_0000_0000_0036, 0x35C9_ADC5_DEA0_0000), defaultSpecifier, defaultFormat, "1000000000000000000000" };
yield return new object[] { new UInt128(0x0013_4261_72C7_4D82, 0x2B87_8FE8_0000_0000), defaultSpecifier, defaultFormat, "100000000000000000000000000000000000" };
yield return new object[] { new UInt128(0x7FFF_FFFF_FFFF_FFFF, 0xFFFF_FFFF_FFFF_FFFF), defaultSpecifier, defaultFormat, "170141183460469231731687303715884105727" };
yield return new object[] { new UInt128(0x8000_0000_0000_0000, 0x0000_0000_0000_0000), defaultSpecifier, defaultFormat, "170141183460469231731687303715884105728" };
yield return new object[] { UInt128.MaxValue, defaultSpecifier, defaultFormat, "340282366920938463463374607431768211455" };
}

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