From bfb982d6824a41ebff1fc5934ebee7f01df1e682 Mon Sep 17 00:00:00 2001
From: dana <dana@dana.is>
Date: Mon, 13 Apr 2026 11:04:58 -0500
Subject: 54318: mathfunc: add isnan() and isinf(). also document NaN + Inf

---
 Doc/Zsh/arith.yo        | 27 +++++++++++++++++++++++++++
 Doc/Zsh/mod_mathfunc.yo |  4 ++--
 2 files changed, 29 insertions(+), 2 deletions(-)

(limited to 'Doc')

diff --git a/Doc/Zsh/arith.yo b/Doc/Zsh/arith.yo
index f8807eb4a..17eb3cc36 100644
--- a/Doc/Zsh/arith.yo
+++ b/Doc/Zsh/arith.yo
@@ -122,6 +122,33 @@ taken for a parameter name.  All numeric parts (before and after the
 decimal point and in the exponent) may contain underscores after the
 leading digit for visual guidance; these are ignored in computation.
 
+The special floating point values NaN (not a number) and infinity are
+fully supported in floating point arithmetic.  They may be produced by
+certain operations, such as division by zero, or referenced explicitly in
+arithmetic constructs and float assignments using the case-insensitive
+constants tt(NaN) and tt(Inf).  Expansion syntax must be used to
+reference a parameter with one of these names in these contexts:
+
+example(% nan=123 INF=456
+% print $LPAR()LPAR() nan RPAR()RPAR() $LPAR()LPAR() INF RPAR()RPAR()
+NaN Inf
+% print $LPAR()LPAR() $nan RPAR()RPAR() $LPAR()LPAR() $INF RPAR()RPAR()
+123 456
+% typeset -F f=nan && typeset -p f
+typeset -F f=NaN
+% typeset -F f=$nan && typeset -p f
+typeset -F f=123.0000000000)
+
+To check whether a value is NaN, either use the tt(isnan) function
+provided by the tt(zsh/mathfunc) module
+or compare it to the string tt(NaN):
+
+example(% zmodload zsh/mathfunc
+% (( isnan(0.0 / 0) )) && print is nan
+is nan
+% typeset -F f=nan && [[ $f == NaN ]] && print is nan
+is nan)
+
 cindex(arithmetic operators)
 cindex(operators, arithmetic)
 An arithmetic expression uses nearly the same syntax and
diff --git a/Doc/Zsh/mod_mathfunc.yo b/Doc/Zsh/mod_mathfunc.yo
index 61aa3decf..b7223e2cf 100644
--- a/Doc/Zsh/mod_mathfunc.yo
+++ b/Doc/Zsh/mod_mathfunc.yo
@@ -27,8 +27,8 @@ tt(floor), tt(gamma), tt(j0), tt(j1), tt(lgamma), tt(log), tt(log10),
 tt(log1p), tt(log2), tt(logb), tt(sin), tt(sinh), tt(sqrt), tt(tan),
 tt(tanh), tt(y0), tt(y1).  The tt(atan) function can optionally take a
 second argument, in which case it behaves like the C function tt(atan2).
-The tt(ilogb) function takes a single floating point argument, but
-returns an integer.
+The tt(ilogb), tt(isinf), and tt(isnan) functions take a single floating
+point argument, but return an integer.
 
 The function tt(signgam) takes no arguments, and returns an integer, which
 is the C variable of the same name, as described in manref(gamma)(3).  Note
-- 
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