sphack own package (1nov10)

git-svn-id: svn://tug.org/texlive/trunk@20313 c570f23f-e606-0410-a88d-b1316a301751

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+% SPHACK.STY
+% Oliver Pretzel  (o.pretzel@ic.ac.uk)
+% Created 22 May 1998, Version 1.0 22May 1998
+% Modified space hacks for LateX (209 and 2e)
+%   (to prevent \label, \index and similar commands
+%    affecting spacing in vertical mode).
+%
+%
+% DOCUMENTATION at end of file
+%
+% ALL RIGHTS RESERVED
+%
+% This file may be distributed freely.
+% It may be modified for local use (please inform me of such modifications)
+% Modified versions may only be distributed if
+% 1. The name is changed
+% 2. A statement acknowledging the modification heads the file.
+%
+% DO NOT USE \neq in this file
+\chardef\neq\the\catcode`\@
+\makeatletter\@makeother\"
+%
+
+\typeout{`sphack.sty <1.0>}
+%*************************
+
+\ifx\@savdim\undefined\let\@savdim\@savsk\newskip\@savsk\fi
+\def\@bsphack{\relax\ifmmode\else\@savsk\lastskip\@savsf\ifhmode\spacefactor
+    \else\lastpenalty\@savdim\prevdepth\removelastskip\fi\fi}
+\def\@esphack{\relax\ifmmode\else\ifvmode\penalty\if@nobreak\@M\else
+    \if@inlabel\@M\else\if@noskipsec\@M\else\@savsf\fi\fi\fi
+    \prevdepth\@savdim\vskip\@savsk\else
+    \spacefactor\@savsf\ifdim\@savsk>\z@\ignorespaces\fi\fi\fi}
+\ifx\LateXe\undefined
+\def\@Esphack{\@esphack\ifhmode\ifdim\@savsk>\z@
+    \global\@ignoretrue\ignorespaces\fi\fi}
+\else
+\def\@Esphack{\@esphack\ifhmode\ifdim\@savsk>\z@
+    \@ignoretrue\ignorespaces\fi\fi}
+\fi
+
+% This line must be last line of code
+\catcode`\@\neq\let\neq\ne\endinput
+
+*******************
+  DOCUMENTATION
+*******************
+Standard LaTeX uses the macros \@bsphack, \@esphack, and \@Esphack, for
+inserts into the text that should be invisible. So, for instance a space
+before and after a \label command should not result in two spaces in the
+output.
+
+LaTeX deals with this as follows
+ in maths mode do nothing,
+ in horizontal mode restore the space factor,
+ if the last thing on the list was a space
+   add \ignorespaces (and (\global)\ignoretrue at the end of an environment),
+ in vertical mode do nothing.
+
+Doing nothing in maths mode is (nearly) harmless because maths mode does its
+own spacing (and anyway hidden commands will usually appear only at the start
+or end of maths).
+
+Doing nothing in vertical mode is not harmless. Many invisible commands such
+as \index may insert delayed write commands into TeX's output (so that page
+numbers are correctly calculated). These commands can cause vertical space to
+accumulate, and may cause a page break; \index is a particular problem in
+LaTeX209 since it inserts a delayed write if an index is actually being built
+(\makeindex in preamble) but does nothing otherwise. That can change the page
+breaks in a document.
+
+It is not possible to solve this problem completely in LaTeX because TeX does
+not remove things from the main vertical list once they have been
+contributed. So LaTeX2e makes \index insert something into the vertical
+list whether the index is being written or not. That has the virtue of
+consistancy, but is far from ideal. For instance, an \index immediately after
+an \item can cause the page to break between the item label and content.
+
+The code above remedies this fault and other common anomalies so that commands
+are nearly always invisible in vertical mode as well. It works as follows:
+
+Rename LaTeX's dimension \@savsk to \@savdim set a new skip \@savsk
+  (because we need a true skip and a dimension in vertical mode)
+
+\@bsphack (at start of invisible command)
+in hmode (non-math)
+   store spacefactor in \@savsf
+   store lastskip in \@savsk (used to test whether space already present)
+in vmode
+   store lastpenalty in \@savsf
+   store lastskip in \@savsk (used for movement)
+   store previous depth  in \@savdim
+   skip back \lastskip
+
+\@esphack (at end of invisible command)
+in hmode (non-math)
+   set spacefactor = \@savsf
+   if \@savsk > \z@ \ignorespaces
+in vmode
+   if in a label, or just after section heading, or if \@nobreak
+      insert infinite penalty, (to prevent a page break)
+   else insert penalty \@savsf
+   endif
+   set previous depth = \@savdim
+   skip \@savsk
+
+Just as in standard LateX, \@Esphack is \@esphack + (\global)\@ignoretrue.
+
+It is not necessary to change any of the label or index macros to fit with
+this code.
+
+End of sphack.sty
+*******************