Simplify, document, and port floating-point.

The porting part of this patch fixes bugs on non-IEEE platforms
with frexp, ldexp, logb.
* admin/CPP-DEFINES (HAVE_CBRT, HAVE_LOGB, logb): Remove.
* configure.ac (logb, cbrt): Do not check for these functions,
as they are not being used.
* doc/lispref/numbers.texi (Float Basics, Arithmetic Operations, Math Functions):
Document that / and mod (with floating point arguments), along
with asin, acos, log, log10, expt and sqrt, return special values
instead of signaling exceptions.
(Float Basics): Document that logb operates on the absolute value
of its argument.
(Math Functions): Document that (log ARG BASE) also returns NaN if
BASE is negative.  Document that (expt X Y) returns NaN if X is a
finite negative number and Y a finite non-integer.
* etc/NEWS: Document NaNs versus signaling-error change.
* src/data.c, src/lisp.h (Qdomain_error, Qsingularity_error, Qunderflow_error):
Now static.
* src/floatfns.c: Simplify discussion of functions that Emacs doesn't
support, by removing commented-out code and briefly listing the
C89 functions excluded.  The commented-out stuff was confusing
maintenance, e.g., we thought we needed cbrt but it was commented out.
(logb): Remove decl; no longer needed.
(isfinite): New macro, if not already supplied.
(isnan): Don't replace any existing macro.
(Ffrexp, Fldexp): Define even if !HAVE_COPYSIGN, as frexp and ldexp
are present on all C89 platforms.
(Ffrexp): Do not special-case zero, as frexp does the right thing
for that case.
(Flogb): Do not use logb, as it doesn't have the desired meaning
on hosts that use non-base-2 floating point.  Instead, stick with
frexp, which is C89 anyway.  Do not pass an infinity or a NaN to
frexp, to avoid getting an unspecified result.

1 files changed, 3 insertions, 3 deletions

diff --git a/configure.ac b/configure.ac
index 97e967d8043..9491c1da8d5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2689,8 +2689,8 @@ if test $emacs_cv_netdb_declares_h_errno = yes; then
   AC_DEFINE(HAVE_H_ERRNO, 1, [Define to 1 if netdb.h declares h_errno.])
 fi
 
-# fmod, logb, and frexp are found in -lm on most systems.
-# On HPUX 9.01, -lm does not contain logb, so check for sqrt.
+# sqrt and other floating-point functions such as fmod and frexp
+# are found in -lm on most systems.
 AC_CHECK_LIB(m, sqrt)
 
 # Check for mail-locking functions in a "mail" library.  Probably this should
@@ -2770,7 +2770,7 @@ AC_SUBST(BLESSMAIL_TARGET)
 
 AC_CHECK_FUNCS(gethostname \
 closedir getrusage get_current_dir_name \
-lrand48 logb cbrt setsid \
+lrand48 setsid \
 fpathconf select euidaccess getpagesize setlocale \
 utimes getrlimit setrlimit setpgid getcwd shutdown getaddrinfo \
 __fpending strsignal setitimer \