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bachotex2008-pawel-jackowski-pearl1.tex

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%%% \badness badness

% \badness parameter is supposed to tell something about box stretch or shrinkage,
% or more precisely, about how far the available stretchability or shrinkability has been used.
% \badness==0 means no stretch or shrink used, 100 means the entire box flexibility consumed,
% more then 100 denotes undefull or overfull box (the later with \badness equal 1000000).
% So \badness certaintly says something about how the content fits the box, but one
% may be surprised by fine artifacts of the actual algorithm. Lets take a macro that measures
% \vbox \badness, taking the actual and the available stretch as arguments.

\def\test#1#2{% <actual_stretch> <available_stretch>
  \setbox0\vbox to\dimexpr#1{\vskip0pt plus\dimexpr#2}%
  \immediate\write16{badness=\the\badness, \the\ht0}}

\test{100pt-1sp}{100pt}  % \badness=99
\test{100pt}{100pt}      % 100
\test{100pt+1sp}{100pt}  % 100
\test{100.3366pt}{100pt} % 100
\test{100.3367pt}{100pt} % 101

% Note that we never get \badness equal 100 if the actual
% stretch is even 1sp smaller then the available stretch.
% But \TeX\ seems to ignore the stretch abuse around 0.0033 and less.

% OK so far. Now lets take such insignificantly underfull box of
% 299sp actual, and 298sp available stretch. We will scale those
% values with in integer factor.

\message{SCALING}

\def\scale#1{\test{299sp*#1}{298sp*#1}}
\scale{1} % \badness=100
\scale{2} % \badness=100
\scale{3} % \badness=100

\scale{24183} % \badness=101
\scale{24184} % \badness=101

\scale{24948} % \badness=100

% \badness varies although we keep the stretch ratio fixed!
% All because heuristic \badness formula (tex.web, line 2320):
%
%   @d inf_bad = 10000 {infinitely bad value}
%   @p function badness(@!t,@!s:scaled):halfword; {compute badness, given |t>=0|}
%   var r:integer; {approximation to $\alpha t/s$, where $\alpha^3\approx
%     100\cdot2^{18}$}
%   begin if t=0 then badness:=0
%   else if s<=0 then badness:=inf_bad
%   else  begin if t<=7230584 then  r:=(t*297) div s {$297^3=99.94\times2^{18}$}
%     else if s>=1663497 then r:=t div (s div 297)
%     else r:=t;
%     if r>1290 then badness:=inf_bad {$1290^3<2^{31}<1291^3$}
%     else badness:=(r*r*r+@'400000) div @'1000000;
%     end; {that was $r^3/2^{18}$, rounded to the nearest integer}
%   end;

\end