\manual DVICLASS(3){}
\name
DVI\_DT, DVI\_OpLen---DVI opcode classification tables
\synopsis
DVI\_DT(code)
int code;

DVI\_OpLen(code)
int code;
\endsyn
\description
These macros compress DVI code values according to `classification'
and `opcode length'.  \i{DVI\_DT} returns one of the following values:

\beginlist{5em}

\listentry{\lit{DT\_CHAR}}
A literal character code ($0 \le code \le 127$).

\listentry{\lit{DT\_SET}}
A \lit{set} code (set a character and advance).

\listentry{\lit{DT\_SETRULE}}
A \lit{set\_rule} code.

\listentry{\lit{DT\_PUT}}
A \lit{put} code (set a character but do not advance).

\listentry{\lit{DT\_PUTRULE}}
A \lit{put\_rule} code (set a rule but do not advance).

\listentry{\lit{DT\_NOP}}
A \lit{nop} code.

\listentry{\lit{DT\_BOP}}
A \lit{bop} code.

\listentry{\lit{DT\_EOP}}
An \lit{eop} code.

\listentry{\lit{DT\_PUSH}}
A \lit{push}.

\listentry{\lit{DT\_POP}}
A \lit{pop}.

\listentry{\lit{DT\_RIGHT}}
Any of the several \lit{right} codes.

\listentry{\lit{DT\_W0}}
A \lit{w0}.

\listentry{\lit{DT\_W}}
One of the \lit{w}s.

\listentry{\lit{DT\_X0}}
An \lit{x0}.

\listentry{\lit{DT\_X}}
One of the \lit{x}s.

\listentry{\lit{DT\_DOWN}}
A \lit{down}.

\listentry{\lit{DT\_Y0}}
A \lit{y0}.

\listentry{\lit{DT\_Y}}
A \lit{y}.

\listentry{\lit{DT\_Z0}}
A \lit{z0}.

\listentry{\lit{DT\_Z}}
A \lit{z}.

\listentry{\lit{DT\_FNTNUM}}
A parameterless font selector (\lit{fntnum0}, \lit{fntnum1}, \dots,
\lit{fntnum63}).

\listentry{\lit{DT\_FNT}}
A parameterised font selector (\lit{fnt1}, \dots, \lit{fnt4}).

\listentry{\lit{DT\_XXX}}
A \lit{xxx}: a special.

\listentry{\lit{DT\_FNTDEF}}
A \lit{fntdef}.

\listentry{\lit{DT\_PRE}}
A \lit{pre}.

\listentry{\lit{DT\_POST}}
A \lit{post}.

\listentry{\lit{DT\_POSTPOST}}
A \lit{postpost}.

\listentry{\lit{DT\_UNDEF}}
An undefined DVI opcode (in $[250..255]$).

\endlist

\i{DVI\_OpLen} returns the length of the first parameter, as one
of the following values:

\beginlist{5em}
\listentry{\lit{DPL\_NONE}}
No (or implicit) parameter, or it cannot be determined so simply, e.g.,
\lit{bop}, or \lit{post}.

\listentry{\lit{DPL\_SGN1}}
A signed one-byte parameter $-128 \le p \le 127$.

\listentry{\lit{DPL\_SGN2}}
A signed two-byte parameter $-32768 \le p \le 32767$.

\listentry{\lit{DPL\_SGN3}}
A signed three-byte parameter $-8388608 \le p \le 8388607$.

\listentry{\lit{DPL\_SGN4}}
A signed four-byte parameter $-2147483648 \le p \le 2147483647$.

\listentry{\lit{DPL\_UNS1}}
An unsigned one-byte parameter $0 \le p \le 255$.

\listentry{\lit{DPL\_UNS2}}
An unsigned two-byte parameter $0 \le p \le 65535$.

\listentry{\lit{DPL\_UNS3}}
An unsigned three-byte parameter $0 \le p \le 16777215$.

\endlist

These values are intended to be used to simplify \lit{switch} statements
that decode DVI files.  A program that must interpret the opcodes can
use code similar to the following:

\vskip 0pt plus1fil
\begincode \vbox{
    op = getc(dvi\_file);
    switch (DVI\_OpLen(op)) {
    case DPL\_NONE:    {\it /* do nothing */}
	break;
    case DPL\_SGN1:    {\it /* get a one byte signed parameter */}
        param = Sign8(getc(dvi\_file));
        break;
    case DPL\_SGN2:    {\it /* get a two byte signed parameter */}
        fGetWord(dvi\_file, param);
        param = Sign16(param);
        break;
    {\rm$\vdots$}
    case DPL\_UNS3:    {\it /* get a three byte unsigned parameter */}
        fGet3Byte(dvi\_file, param);
        break;
    }

    switch (DVI\_DT(op)) {
    case DT\_CHAR:
        set\_char\_and\_advance(op);
        break;
    case DT\_SET:
        set\_char\_and\_advance(param);
        break;
    {\rm$\vdots$}
    }
} \endcode

In other words, ## other words ##