Re: [Groff] Integer arithmetic

[Ted Harding]

Further to my previous post, first here is a revision of
the .PS and .PE macros in the 'ms' macro set which allow
the use of ".PS T" so as to (effectively) suppress any
effect on the printed page. It is assumed that no drawing
is done during a call to ".PS T <....> .PE".

--8<-- cut here -------------------------------------
.de PS
.nr Tacit 0
.ie  \\n[.$]<3 \{\
.br
.sp \\n[DD]u
.ie \\n[.$]<2 address@hidden bad arguments to PS (not preprocessed with pic?)
.el \{\
.       address@hidden (u;\\$1)+1v
.       in +(u;\\n[.l]-\\n[.i]-\\$2/2>?0)
.   \}
.HTML-IMAGE
.\}
.el \{\
.if '\\$3'T' \{\
.nr Tacit 1
.   \}
.\}
..
.de PE
.ie 1-\\n[Tacit] \{\
.HTML-IMAGE-END
address@hidden
.sp \\n[DD]u+.5m
.\}
.el \{\
.nr Tacit 0
.sp -1
.\}
..
--8<-- cut here -------------------------------------

Then, if you do something like

.LP
Calulation by PIC
.PS T
h  = 105.5
wc =h*0.36
wu = h*0.36*72000/25.4
command ".ds wstring " sprintf("%.7f",wu)
command ".nr wnumber " wc/10 "c"
.PE
wstring: \*[wstring]
.br
wnumber: \n[wnumber]
.br
Calculation by PIC


you should get the four lines of text without any extra spacing
(i.e. the action of PIC is "invisible").

Regarding remarks by other concerning re-programming gtroff so
that it does its arithmetic in reals rather than integers, I have
to say that once -- a long time ago -- I looked into this.
It seemed to me that the use of integer arithmetic was so deeply
and extensively dispersed throughout troff that it would have
meant, in effect, a complete re-write of nearly everything!

So I have put up with the integer arithmetic for most of the
"routine" internal calculations (such as scaling sizes or distances),
but use PIC (in the sort of weay illustrated) when using real
arithmetic really matters. Mostly, this is in connection with
drawing graphs anyway, but on occasion I use it to calculate
statistical tables for output (using PIC's "command" command)
to be interpreted by TBL (provided you invoke them in the
recommended order pic | tbl | eqn).

Regarding heirloom troff, I have read through the user manual
(Gunnar Ritter's revision and extension of the original Ossanna
and kernighan manual) without finding a statement that heirloom
troff does real arithmetic rather than integer (the main difference
noted is that you can call for fractional point-sizes). There is
of course the usual possibiloity to use fractional multiples of
distance units, such a "1.25i" or "3.45c" etc.

The only occurrence of the word "arithmetic" is in the section
"1.4 Numerical expressions" where this issue is not mentioned,
though all the arithmetic operators are discussed.

Perhaps Gunnar could comment?

Best wishes to all,
Ted.



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E-Mail: (Ted Harding) <address@hidden>
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Date: 15-Oct-09                                       Time: 22:07:20
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