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.

2 files changed, 5 insertions, 4 deletions

diff --git a/admin/CPP-DEFINES b/admin/CPP-DEFINES
index b40ba78e20d..cf6ffee2c63 100644
--- a/admin/CPP-DEFINES
+++ b/admin/CPP-DEFINES
@@ -120,7 +120,6 @@ HAVE_ATTRIBUTE_ALIGNED
 HAVE_BDFFONT
 HAVE_BOXES
 HAVE_C99_STRTOLD
-HAVE_CBRT
 HAVE_CFMAKERAW
 HAVE_CFSETSPEED
 HAVE_CLOCK_GETTIME
@@ -251,7 +250,6 @@ HAVE_LIBXMU
 HAVE_LINUX_VERSION_H
 HAVE_LOCALTIME_R
 HAVE_LOCAL_SOCKETS
-HAVE_LOGB
 HAVE_LONG_FILE_NAMES
 HAVE_LONG_LONG_INT
 HAVE_LRAND48
@@ -574,7 +572,6 @@ getpid
 isatty
 kill
 link
-logb
 lseek
 mkdir
 mktemp
@@ -616,7 +613,6 @@ fopen
 getpid
 index
 isatty
-logb
 lseek
 mkdir
 mktemp
diff --git a/admin/ChangeLog b/admin/ChangeLog
index 2c61f437981..b70067d7465 100644
--- a/admin/ChangeLog
+++ b/admin/ChangeLog
@@ -1,3 +1,8 @@
+2012-09-11  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Simplify, document, and port floating-point (Bug#12381).
+        * CPP-DEFINES (HAVE_CBRT, HAVE_LOGB, logb): Remove.
+
 2012-09-09  Paul Eggert  <eggert@cs.ucla.edu>
 
         Assume C89 or later for math functions (Bug#12381).