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Remove overhead from RomanNumeralExtensions #1508

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May 28, 2024
Merged

Remove overhead from RomanNumeralExtensions #1508

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94 changes: 41 additions & 53 deletions src/Humanizer/RomanNumeralExtensions.cs
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Original file line number Diff line number Diff line change
@@ -1,60 +1,50 @@
// Done by Jesse Slicer https://github.com/jslicer

using System.Diagnostics;

namespace Humanizer;

/// <summary>
/// Contains extension methods for changing a number to Roman representation (ToRoman) and from Roman representation back to the number (FromRoman)
/// </summary>
public static class RomanNumeralExtensions
{
static readonly Dictionary<string, int> RomanNumerals =
new(StringComparer.OrdinalIgnoreCase)
static readonly KeyValuePair<string, int>[] RomanNumeralsSequence =
[
new KeyValuePair<string, int>("M", 1000),
new KeyValuePair<string, int>("CM", 900),
new KeyValuePair<string, int>("D", 500 ),
new KeyValuePair<string, int>("CD", 400),
new KeyValuePair<string, int>("C", 100 ),
new KeyValuePair<string, int>("XC", 90 ),
new KeyValuePair<string, int>("L", 50 ),
new KeyValuePair<string, int>("XL", 40 ),
new KeyValuePair<string, int>("X", 10 ),
new KeyValuePair<string, int>("IX", 9 ),
new KeyValuePair<string, int>("V", 5 ),
new KeyValuePair<string, int>("IV", 4 ),
new KeyValuePair<string, int>("I", 1 ),
];

static int GetRomanNumeralCharValue(char c)
{
Debug.Assert(char.ToLowerInvariant(c) is 'M' or 'D' or 'C' or 'L' or 'X' or 'V' or 'I', "Invalid Roman numeral character");
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return (c & ~0x20) switch
{
{
"M", 1000
},
{
"CM", 900
},
{
"D", 500
},
{
"CD", 400
},
{
"C", 100
},
{
"XC", 90
},
{
"L", 50
},
{
"XL", 40
},
{
"X", 10
},
{
"IX", 9
},
{
"V", 5
},
{
"IV", 4
},
{
"I", 1
}
'M' => 1000,
'D' => 500,
'C' => 100,
'L' => 50,
'X' => 10,
'V' => 5,
_ => 1,
};
}

static readonly Regex ValidRomanNumeral =
new(
"^(?i:(?=[MDCLXVI])((M{0,3})((C[DM])|(D?C{0,3}))?((X[LC])|(L?XX{0,2})|L)?((I[VX])|(V?(II{0,2}))|V)?))$",
RegexOptions.Compiled | RegexOptions.IgnoreCase);
RegexOptions.Compiled | RegexOptions.ExplicitCapture | RegexOptions.IgnoreCase | RegexOptions.CultureInvariant);

/// <summary>
/// Converts Roman numbers into integer
Expand Down Expand Up @@ -92,14 +82,10 @@ public static int FromRoman(CharSpan input)

while (i > 0)
{
var digit = RomanNumerals[input[--i]
.ToString()];

var digit = GetRomanNumeralCharValue(input[--i]);
if (i > 0)
{
var previousDigit = RomanNumerals[input[i - 1]
.ToString()];

var previousDigit = GetRomanNumeralCharValue(input[i - 1]);
if (previousDigit < digit)
{
digit -= previousDigit;
Expand Down Expand Up @@ -130,18 +116,20 @@ public static string ToRoman(this int input)
throw new ArgumentOutOfRangeException();
}

var builder = new StringBuilder(maxRomanNumeralLength);
Span<char> builder = stackalloc char[maxRomanNumeralLength];
var pos = 0;

foreach (var pair in RomanNumerals)
foreach (var pair in RomanNumeralsSequence)
{
while (input / pair.Value > 0)
while (input >= pair.Value)
{
builder.Append(pair.Key);
pair.Key.AsSpan().CopyTo(builder.Slice(pos));
pos += pair.Key.Length;
input -= pair.Value;
}
}

return builder.ToString();
return builder.Slice(0, pos).ToString();
}

static bool IsInvalidRomanNumeral(CharSpan input) =>
Expand Down