sort: use long doubles for general numeric mode

* src/sort.c (general_numcompare): Use long doubles unconditionally,
and strtold when available, to convert numbers with greater range and
precision.  Performance was seen to be on par with standard doubles.
* doc/coreutils.texi (sort invocation): Amend the -g description to
mention long double rather than double, and strtold rather than strtod.
* src/getlimits.c (main): Output floating point limits for use in tests.
* tests/misc/sort-float: A new test to ensure sort is using long
doubles when possible, and that locale specific floats are handled.
* tests/Makefile.am: Reference the new test.
* tests/test-lib.sh (getlimits_): Normalize indenting.
* NEWS: Mention the new behaviour.
Reported by Nelson Beebe.

2 files changed, 21 insertions, 5 deletions

diff --git a/src/getlimits.c b/src/getlimits.c
index 48d07b5ae..93d4035a7 100644
--- a/src/getlimits.c
+++ b/src/getlimits.c
@@ -19,6 +19,7 @@
 #include <config.h>             /* sets _FILE_OFFSET_BITS=64 etc. */
 #include <stdio.h>
 #include <sys/types.h>
+#include <float.h>
 
 #include "system.h"
 #include "c-ctype.h"
@@ -123,7 +124,7 @@ decimal_ascii_add (const char *str1, const char *str2)
 int
 main (int argc, char **argv)
 {
-  char limit[64];               /* big enough for 128 bit at least */
+  char limit[64];               /* big enough for 128 bit integers at least */
   char *oflow;
 
   initialize_main (&argc, &argv);
@@ -139,20 +140,24 @@ main (int argc, char **argv)
                       usage, AUTHORS, (char const *) NULL);
 
 #define print_int(TYPE)                                                  \
-  snprintf (limit, sizeof limit, "%"PRIuMAX, (uintmax_t)TYPE##_MAX);    \
+  snprintf (limit, sizeof limit, "%"PRIuMAX, (uintmax_t)TYPE##_MAX);     \
   printf (#TYPE"_MAX=%s\n", limit);                                      \
   oflow = decimal_ascii_add (limit, "1");                                \
   printf (#TYPE"_OFLOW=%s\n", oflow);                                    \
   free (oflow);                                                          \
   if (TYPE##_MIN)                                                        \
     {                                                                    \
-      snprintf (limit, sizeof limit, "%"PRIdMAX, (intmax_t)TYPE##_MIN); \
+      snprintf (limit, sizeof limit, "%"PRIdMAX, (intmax_t)TYPE##_MIN);  \
       printf (#TYPE"_MIN=%s\n", limit);                                  \
       oflow = decimal_ascii_add (limit, "-1");                           \
       printf (#TYPE"_UFLOW=%s\n", oflow);                                \
       free (oflow);                                                      \
     }
 
+#define print_float(TYPE)                                                \
+  printf (#TYPE"_MIN=%Le\n", (long double)TYPE##_MIN);                   \
+  printf (#TYPE"_MAX=%Le\n", (long double)TYPE##_MAX);
+
   /* Variable sized ints */
   print_int (CHAR);
   print_int (SCHAR);
@@ -171,4 +176,9 @@ main (int argc, char **argv)
   print_int (OFF_T);
   print_int (INTMAX);
   print_int (UINTMAX);
+
+  /* Variable sized floats */
+  print_float (FLT);
+  print_float (DBL);
+  print_float (LDBL);
 }
diff --git a/src/sort.c b/src/sort.c
index 6d47b794b..a81524470 100644
--- a/src/sort.c
+++ b/src/sort.c
@@ -1855,10 +1855,16 @@ general_numcompare (const char *sa, const char *sb)
   /* FIXME: maybe add option to try expensive FP conversion
      only if A and B can't be compared more cheaply/accurately.  */
 
+#if HAVE_C99_STRTOLD /* provided by c-strtold module.  */
+# define STRTOD strtold
+#else
+# define STRTOD strtod
+#endif
+
   char *ea;
   char *eb;
-  double a = strtod (sa, &ea);
-  double b = strtod (sb, &eb);
+  long double a = STRTOD (sa, &ea);
+  long double b = STRTOD (sb, &eb);
 
   /* Put conversion errors at the start of the collating sequence.  */
   if (sa == ea)