History and Acknowledgements
============================

Calc was originally started as a two-week project to occupy a lull in
the author's schedule.  Basically, a friend asked if I remembered the
value of `2^32'.  I didn't offhand, but I said, "that's easy, just
call up an `xcalc'."  `Xcalc' duly reported that the answer to our
question was `4.294967e+09'---with no way to see the full ten digits
even though we knew they were there in the program's memory!  I was so
annoyed, I vowed to write a calculator of my own, once and for all.

I chose Emacs Lisp, a) because I had always been curious about it and
b) because, being only a text editor extension language after all,
Emacs Lisp would surely reach its limits long before the project got
too far out of hand.

To make a long story short, Emacs Lisp turned out to be a
distressingly solid implementation of Lisp, and the humble task of
calculating turned out to be more open-ended than one might have
expected.

Emacs Lisp doesn't have built-in floating point math, so it had to be
simulated in software.  In fact, Emacs integers will only comfortably
fit six decimal digits or so--not enough for a decent calculator.  So
I had to write my own high-precision integer code as well, and once I
had this I figured that arbitrary-size integers were just as easy as
large integers.  Arbitrary floating-point precision was the logical
next step.  Also, since the large integer arithmetic was there anyway
it seemed only fair to give the user direct access to it, which in
turn made it practical to support fractions as well as floats.  All
these features inspired me to look around for other data types that
might be worth having.

Around this time, my friend Rick Koshi showed me his nifty new HP-28
calculator.  It allowed the user to manipulate formulas as well as
numerical quantities, and it could also operate on matrices.  I
decided that these would be good for Calc to have, too.  And once
things had gone this far, I figured I might as well take a look at
serious algebra systems like Mathematica, Macsyma, and Maple for
further ideas.  Since these systems did far more than I could ever
hope to implement, I decided to focus on rewrite rules and other
programming features so that users could implement what they needed
for themselves.

Rick complained that matrices were hard to read, so I put in code to
format them in a 2D style.  Once these routines were in place, Big
mode was obligatory.  Gee, what other language modes would be useful?

Scott Hemphill and Allen Knutson, two friends with a strong
mathematical bent, contributed ideas and algorithms for a number of
Calc features including modulo forms, primality testing, and
float-to-fraction conversion.

Units were added at the eager insistence of Mass Sivilotti.  Later,
Ulrich Mueller at CERN and Przemek Klosowski at NIST provided
invaluable expert assistance with the units table.  As far as I can
remember, the idea of using algebraic formulas and variables to
represent units dates back to an ancient article in Byte magazine
about muMath, an early algebra system for microcomputers.

Many people have contributed to Calc by reporting bugs and suggesting
features, large and small.  A few deserve special mention: Tim Peters,
who helped develop the ideas that led to the selection commands,
rewrite rules, and many other algebra features; Francois Pinard, who
contributed an early prototype of the Calc Summary appendix as well as
providing valuable suggestions in many other areas of Calc; Carl
Witty, whose eagle eyes discovered many typographical and factual
errors in the Calc manual; Tim Kay, who drove the development of
Embedded mode; Ove Ewerlid, who made many suggestions relating to the
algebra commands and contributed some code for polynomial operations;
Randal Schwartz, who suggested the `calc-eval' function; Robert
J. Chassell, who suggested the Calc Tutorial and exercises; and Juha
Sarlin, who first worked out how to split Calc into quickly-loading
parts.  Bob Weiner helped immensely with the Lucid Emacs port.

Among the books used in the development of Calc were Knuth's *Art of
Computer Programming* (especially volume II, *Seminumerical
Algorithms*); *Numerical Recipes* by Press, Flannery, Teukolsky, and
Vetterling; Bevington's *Data Reduction and Error Analysis for the
Physical Sciences*; *Concrete Mathematics* by Graham, Knuth, and
Patashnik; Steele's *Common Lisp, the Language*; the *CRC Standard
Math Tables* (William H. Beyer, ed.); and Abramowitz and Stegun's
venerable *Handbook of Mathematical Functions*.  I consulted the
user's manuals for the HP-28 and HP-48 calculators, as well as for the
programs Mathematica, SMP, Macsyma, Maple, MathCAD, Gnuplot, and
others.  Also, of course, Calc could not have been written without the
excellent *GNU Emacs Lisp Reference Manual*, by Bil Lewis and Dan
LaLiberte.

Final thanks go to Richard Stallman, without whose fine
implementations of the Emacs editor, language, and environment, Calc
would have been finished in two weeks.