% File:      engord.sty
% Version:   2000/05/23 v1.0
% Author:    Heiko Oberdiek <oberdiek@ruf.uni-freiburg.de>
%
% Function:  Converts numbers to english ordinal numbers.
%
% Copyright: Copyright (C) 2000 Heiko Oberdiek.
%
%   This program may be distributed and/or modified under
%   the conditions of the LaTeX Project Public License,
%   either version 1.2 of this license or (at your option)
%   any later version. The latest version of this license
%   is in
%     http://www.latex-project.org/lppl.txt
%   and version 1.2 or later is part of all distributions
%   of LaTeX version 1999/12/01 or later.
%
% Use:
%   * \engord{<LaTeX counter name>}
%     It prints the value of the LaTeX counter as English
%     ordinal number. It can be used so as \arabic, \roman,
%     or \alph.
%   * \engordnumber{<any TeX number>}
%     It prints the number as English ordinal number.
%   * \engordletters#1
%     This command formats the English ordinal letters
%     after the number. It defaults to \textsuperscript.
%   * \engorderror#1
%     It can be redefined, if an other error handling is
%     wanted. The argument is a negative number or zero.
%
% Examples:
%   * \engordnumber{1}   ==> 1st
%     \engordnumber{12}  ==> 12th
%     \engordnumber{123} ==> 123rd
%     \engord{page}      ==> 1st (if page has the value of one)
%   * The default output of a counter can be redefined:
%       \newcounter{mycounter}
%       \renewcommand{\theengcounter}{\engord{mycounter}}
%   * Because the implementation of \engord and \engordnumber
%     is kept expandable, these commands can be used to make
%     command names with an appropriate definition of
%     \engordletters:
%       \renewcommand*{\engordletters}[#1]{#1}
%       \@namedef{My\engordnumber{3}Command}{...}
%     This generates the command name `\My4rdCommand'.
%   * If the letters should not be raised, \engordletters
%     can be redefined as follows:
%       \renewcommand*{\engordletters}[1]{#1}
%
% History:
%   2000/05/23 v1.0: first public release
%
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{engord}%
  [2000/05/23 v1.0 English ordinal numbers (HO)]

% \engordletters is called with one argument, the english
% ord letters, and contains the code to format them. It
% defaults to \textsuperscript:
\providecommand{\ordletters}{\textsuperscript}

% \engorderror is called, if the number is zero
% or negative.
\providecommand*{\engorderror}[1]{%
  #1\ordletters{!ERROR!}%
  \PackageWarning{engord}{%
    `#1' is not an ordinal number%
  }%
}

% \engord expects a LaTeX counter name as argument and
% calls \engordnumber
\newcommand*{\engord}[1]{%
  \engordnumber{\value{#1}}%
}

% \engordnumber is the user command to print a number as
% english ordinal number. The argument can be any
% TeX number like explicit numbers, register values, ...
%
% In a safe way it converts the TeX number argument
% into a form that only consists of decimal digits
\newcommand*{\engordnumber}[1]{%
  \expandafter\EO@number\expandafter{\number#1}%
}

% \EO@number expects a number with decimal digits as
% argument and looks at the size of the number and
% the count of the digits:
\def\EO@number#1{%
  \ifnum#1<1 % handle the error case
    \engorderror{#1}%
  \else
    \ifnum#1<21
      \EO@ord{#1}%
    \else
      \ifnum#1<100
        \EO@twodigits#1%
      \else
        \@ReturnAfterFi{%
          \EO@reverse#1\@nil{}\EO@afterreverse
        }%
      \fi
    \fi
  \fi
}

% An internal help macro to prevent a too deep \if nesting.
\long\def\@ReturnAfterFi#1\fi{\fi#1}

% \EO@ord prints the number with ord letters
% #1: decimal digits, #1 < 21
\def\EO@ord#1{%
  #1%
  \expandafter\ordletters
  \ifcase#1\or
    {st}\or
    {nd}\or
    {rd}\else
    {th}%
  \fi
}

% \EO@twodigits expects a number with two digits,
% 20 < number < 100
\def\EO@twodigits#1#2{%
  #1\EO@ord{#2}%
}

% \EO@reverse reverses the digits of the number
% #1: next digit
% #2: rest of the digits
% #3: already reversed digits
% #4: next command to call with the reversed number
%     as argument
\def\EO@reverse#1#2\@nil#3#4{%
  \ifx\\#2\\%
    #4{#1#3}%
  \else
    \@ReturnAfterFi{%
      \EO@reverse#2\@nil{#1#3}{#4}%
    }%
  \fi
}

% \EO@afterreverse calls \EO@reverseback so that
% \EO@reverseback can inspect the digits of the number
\def\EO@afterreverse#1{%
  \EO@reverseback#1\@nil
}

% \EO@reverseback reverses the reversion
% #1: the last digit of the number
% #2: the second last digit of the number
% #3: first digits of the number in reversed order,
%     it is not empty, because \EO@reverseback is
%     only called with numbers > 100.
\def\EO@reverseback#1#2#3\@nil{%
  \EO@reverse#3\@nil{}\@firstofone
  \ifnum#2#1<21
    \EO@ord{#2#1}%
  \else
    #2\EO@ord{#1}%
  \fi
}

\endinput