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rpn.1: made more precise

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Emma Tebibyte 2024-02-02 20:12:12 -07:00
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@ -1,4 +1,5 @@
.\" Copyright (c) 2024 Emma Tebibyte <emma@tebibyte.media>
.\" Copyright (c) 2024 DTB <trinity@trinity.moe>
.\"
.\" This work is licensed under CC BY-SA 4.0. To see a copy of this license,
.\" visit <http://creativecommons.org/licenses/by-sa/4.0/>.
@ -7,47 +8,48 @@
.SH NAME
npc \(en reverse polish notation evaluation
rpn \(en reverse polish notation evaluation
.SH SYNOPSIS
rpn [integers...] [operations...]
rpn
.RB [numbers...]\ [operators...]
.SH DESCRIPTION
Rpn parses reverse polish notation and adds characters to the stack until there
is an operation. See rpn(7) for more details on the syntax of reverse polish
notation.
Rpn parses and and evaluates reverse polish notation either from the standard
input or by parsing its arguments. See the STANDARD INPUT section.
For information on for reverse polish notation syntax, see rpn(7).
.SH STANDARD INPUT
If rpn is passed arguments, it interprets those arguments as an expression to
be evaluated. Otherwise, it reads characters from standard input to add to the
stack.
If rpn is passed arguments, it interprets them as an expression to be evaluated.
Otherwise, it reads whitespace-delimited numbers and operations from the
standard input.
.SH CAVEATS
Due to precision constraints and the way floats are represented in accordance
with the IEEE Standard for Floating Point Arithmetic (IEEE 754), floating-point
arithmetic has rounding errors. This is somewhat curbed by using the
second-highest float that can be represented in line with this standard to round
numbers to before outputting.
.SH DIAGNOSTICS
If encountering a syntax error, rpn will exit with the appropriate error code
as defined by sysexits.h(3) and print an error message.
.SH CAVEATS
Due to the complexity of integer storage in memory, rpn is only capable of
parsing decimal integers.
Additionally, due to the laws of physics, floating-point math can only be as
precise as slightly less than the machine epsilon of the hardware on which rpn
is running.
.SH RATIONALE
POSIX has its own calculator in the form of bc(1p), which uses standard input
for its calculations. Pair the clunkiness of piping expressions into it and its
use of standard notation, it was clear what rpn should be.
There are no mathematics in the qi(1) shell because it was decided early on that
math was the job of a specific tool and not the shell itself. Thus, rpn was
born.
An infix notation calculation utility, bc(1p), is included in the POSIX
standard, but it doesn’t accept expressions as arguments; in scripts, any
predefined, non-interactive input must be piped into the program. A dc(1)
pre-dates the standardized bc(1p), the latter originally being a preprocessor
for the former, and was included in UNIX v2 onward. While it implements reverse
polish notation, it still suffers from being unable to accept an expression as
an argument.
.SH AUTHOR
@ -60,4 +62,4 @@ Copyright (c) 2024 Emma Tebibyte. License AGPLv3+: GNU AGPL version 3 or later
.SH SEE ALSO
bc(1p), dc(1)
rpn(7), bc(1p), dc(1), IEEE 754