Substitute a <ieee754.h> on hosts lacking it

* .gitignore: Add lib/ieee754.h.
* admin/merge-gnulib (GNULIB_MODULES): Add ieee754-h.
* configure.ac: Remove ieee754.h check, as Gnulib now does that.
* etc/NEWS: Mention this.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.
* lib/ieee754.in.h, m4/ieee754-h.m4: New files, from Gnulib.
* src/lisp.h (IEEE_FLOATING_POINT): Now a macro so that it
can be used in #if.
* src/lread.c, src/print.c: Include <ieee754.h> if
IEEE_FLOATING_POINT, not if HAVE_IEEE754_H.
* src/lread.c (string_to_number):
* src/print.c (float_to_string):
Process NaNs only on IEEE hosts, and assume <ieee754.h>
in that case.

1 files changed, 3 insertions, 6 deletions

diff --git a/src/lread.c b/src/lread.c
index 290b0f6bbe9..9a025d8664d 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -72,7 +72,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #define file_tell ftell
 #endif
 
-#if HAVE_IEEE754_H
+#if IEEE_FLOATING_POINT
 # include <ieee754.h>
 #endif
 
@@ -3756,21 +3756,18 @@ string_to_number (char const *string, int base, int flags)
               cp += 3;
               value = INFINITY;
             }
+#if IEEE_FLOATING_POINT
           else if (cp[-1] == '+'
                    && cp[0] == 'N' && cp[1] == 'a' && cp[2] == 'N')
             {
               state |= E_EXP;
               cp += 3;
-#if HAVE_IEEE754_H
               union ieee754_double u
                 = { .ieee_nan = { .exponent = -1, .quiet_nan = 1,
                                   .mantissa0 = n >> 31 >> 1, .mantissa1 = n }};
               value = u.d;
-#else
-              /* NAN is a "positive" NaN on all known Emacs hosts.  */
-              value = NAN;
-#endif
             }
+#endif
           else
             cp = ecp;
         }