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digitalmars.D.bugs - [Issue 3230] New: std.conv should provide facilities for converting from Roman numerals.

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3230

           Summary: std.conv should provide facilities for converting from
                    Roman numerals.
           Product: D
           Version: 2.031
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: patch
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: dsimcha yahoo.com


Pretty simple, without further ado here's the patch.  Just to be absolutely
clear, I wrote this code snippet entirely by myself and hereby release it into
the public domain.

// Converts a single digit from Roman to arabic.
private uint convertDigit(char digit) pure {
    switch(digit) {
        case 'I' :
            return 1;
        case 'V' :
            return 5;
        case 'X' :
            return 10;
        case 'L' :
            return 50;
        case 'C' :
            return 100;
        case 'D' :
            return 500;
        case 'M' :
            return 1000;
        default :
            throw new ConvError(
                "Could not convert Roman digit " ~ digit ~ " to a number.");
    }
    assert(0);
}

/**Converts a string containing a Roman numeral to an unsigned integer
 * representation.
 *
 * Throws:  ConvError on invalid Roman digit.
 */
uint romanToInt(const char[] roman) pure {
    uint result = 0;
    uint maxDigit = 0;

    for(size_t i = roman.length - 1; i != size_t.max; i--) {
        auto romanDigit = roman[i];
        uint arabic = convertDigit(romanDigit);

        if(arabic > maxDigit) {
            maxDigit = arabic;
        }

        // Should we add or subtract?
        if(arabic >= maxDigit) {
            result += arabic;
        } else {
            result -= arabic;
        }
    }
    return result;
}

unittest {
    assert(romanToInt("XIX") == 19);
    assert(romanToInt("DCLXVI") == 666);
    assert(romanToInt("XXX") == 30);
    assert(romanToInt("MDCCCLXXXVIII") == 1888);
    assert(romanToInt("XCIX") == 99);
    assert(romanToInt("XLIX") == 49);
    assert(romanToInt("IV") == 4);
    assert(romanToInt("XLV") == 45);
}

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Aug 05 2009
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3230


Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug yahoo.com.au


--- Comment #1 from Don <clugdbug yahoo.com.au> 2009-09-08 09:46:17 PDT ---
Is this sufficiently commonly used that it belongs in the standard library? My
feeling is that the standard library would need to get very large before this
sort of stuff is in there. Do other languages include it?

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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3230


Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |andrei metalanguage.com
         AssignedTo|nobody puremagic.com        |andrei metalanguage.com


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Oct 11 2009
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3230


Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |WONTFIX


--- Comment #2 from Andrei Alexandrescu <andrei metalanguage.com> 2010-10-02
19:05:30 PDT ---
This is a bit too exotic for inclusion in the standard library. If people feel
differently, please reopen and discuss.

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