doublespace.sty

\def\baselinestretch{2}

\def\setstretch#1{\renewcommand{\baselinestretch}{#1}}

\def\singlespace{\def\baselinestretch{1}\@normalsize}
\def\endsinglespace{}

\def\@setsize#1#2#3#4{\@nomath#1\let\@currsize#1\baselineskip
 #2\baselineskip\baselinestretch\baselineskip
 \setbox\strutbox\hbox{\vrule height.7\baselineskip
 depth.3\baselineskip width\z@}
 \normalbaselineskip\baselineskip#3#4}

\skip\footins 20pt plus4pt minus4pt

\def\@xfloat#1[#2]{\ifhmode \@bsphack\@floatpenalty -\@Mii\else
 \@floatpenalty-\@Miii\fi\def\@captype{#1}\ifinner
 \@parmoderr\@floatpenalty\z@
 \else\@next\@currbox\@freelist{\@tempcnta\csname ftype@#1\endcsname
 \multiply\@tempcnta\@xxxii\advance\@tempcnta\sixt@@n
 \@tfor \@tempa :=#2\do
 {\if\@tempa h\advance\@tempcnta \@ne\fi
 \if\@tempa t\advance\@tempcnta \tw@\fi
 \if\@tempa b\advance\@tempcnta 4\relax\fi
 \if\@tempa p\advance\@tempcnta 8\relax\fi
 }\global\count\@currbox\@tempcnta}\@fltovf\fi
 \global\setbox\@currbox\vbox\bgroup
 \def\baselinestretch{1}\@normalsize
 \boxmaxdepth\z@
 \hsize\columnwidth \@parboxrestore}
\long\def\@footnotetext#1{\insert\footins{\def\baselinestretch{1}\footnotesize
 \interlinepenalty\interfootnotelinepenalty
 \splittopskip\footnotesep
 \splitmaxdepth \dp\strutbox \floatingpenalty \@MM
 \hsize\columnwidth \@parboxrestore
 \edef\@currentlabel{\csname p@footnote\endcsname\@thefnmark}\@makefntext
 {\rule{\z@}{\footnotesep}\ignorespaces
 #1\strut}}}