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.

3 files changed, 10 insertions, 35 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 96de60e4670..bdece817bd6 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -2670,17 +2670,14 @@ XFLOAT_DATA (Lisp_Object f)
 
 /* Most hosts nowadays use IEEE floating point, so they use IEC 60559
    representations, have infinities and NaNs, and do not trap on
-   exceptions.  Define IEEE_FLOATING_POINT if this host is one of the
+   exceptions.  Define IEEE_FLOATING_POINT to 1 if this host is one of the
    typical ones.  The C11 macro __STDC_IEC_559__ is close to what is
    wanted here, but is not quite right because Emacs does not require
    all the features of C11 Annex F (and does not require C11 at all,
    for that matter).  */
-enum
-  {
-    IEEE_FLOATING_POINT
-      = (FLT_RADIX == 2 && FLT_MANT_DIG == 24
-         && FLT_MIN_EXP == -125 && FLT_MAX_EXP == 128)
-  };
+
+#define IEEE_FLOATING_POINT (FLT_RADIX == 2 && FLT_MANT_DIG == 24 \
+                             && FLT_MIN_EXP == -125 && FLT_MAX_EXP == 128)
 
 /* A character, declared with the following typedef, is a member
    of some character set associated with the current buffer.  */
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;
         }
diff --git a/src/print.c b/src/print.c
index add21609cc5..34c7fa12b6e 100644
--- a/src/print.c
+++ b/src/print.c
@@ -40,7 +40,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <ftoastr.h>
 #include <math.h>
 
-#if HAVE_IEEE754_H
+#if IEEE_FLOATING_POINT
 # include <ieee754.h>
 #endif
 
@@ -1013,34 +1013,15 @@ float_to_string (char *buf, double data)
       strcpy (buf, minus_infinity_string + positive);
       return sizeof minus_infinity_string - 1 - positive;
     }
+#if IEEE_FLOATING_POINT
   if (isnan (data))
     {
-#if HAVE_IEEE754_H
       union ieee754_double u = { .d = data };
       uprintmax_t hi = u.ieee_nan.mantissa0;
       return sprintf (buf, &"-%"pMu".0e+NaN"[!u.ieee_nan.negative],
                       (hi << 31 << 1) + u.ieee_nan.mantissa1);
-#else
-      /* Prepend "-" if the NaN's sign bit is negative.
-         The sign bit of a double is the bit that is 1 in -0.0.  */
-      static char const NaN_string[] = "0.0e+NaN";
-      int i;
-      union { double d; char c[sizeof (double)]; } u_data, u_minus_zero;
-      bool negative = 0;
-      u_data.d = data;
-      u_minus_zero.d = - 0.0;
-      for (i = 0; i < sizeof (double); i++)
-        if (u_data.c[i] & u_minus_zero.c[i])
-          {
-            *buf = '-';
-            negative = 1;
-            break;
-          }
-
-      strcpy (buf + negative, NaN_string);
-      return negative + sizeof NaN_string - 1;
-#endif
     }
+#endif
 
   if (NILP (Vfloat_output_format)
       || !STRINGP (Vfloat_output_format))