5 files changed, 31 insertions, 7 deletions
diff --git a/misc/efgcvt.c b/misc/efgcvt.c
index 9348914ff2..dc711c63dc 100644
--- a/misc/efgcvt.c
+++ b/misc/efgcvt.c
@@ -17,6 +17,7 @@
    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.  */
 
+#include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/param.h>
@@ -29,8 +30,13 @@
 # define FLOAT_FMT_FLAG
 /* Actually we have to write (DBL_DIG + log10 (DBL_MAX_10_EXP)) but we
    don't have log10 available in the preprocessor.  */
-# define MAXDIG (DBL_DIG + 3)
-# define NDIGIT_MAX DBL_DIG
+# define MAXDIG (NDIGIT_MAX + 3)
+# if DBL_MANT_DIG == 53
+#  define NDIGIT_MAX 17
+# else
+/* See IEEE 854 5.6, table 2 for this formula.  */
+#  define NDIGIT_MAX (lrint (ceil (M_LN2 / M_LN10 * DBL_MANT_DIG + 1.0)))
+# endif
 #endif
 
 #define APPEND(a, b) APPEND2 (a, b)
diff --git a/misc/efgcvt_r.c b/misc/efgcvt_r.c
index 944fe4cc98..d73fd22f70 100644
--- a/misc/efgcvt_r.c
+++ b/misc/efgcvt_r.c
@@ -30,7 +30,12 @@
 # define FUNC_PREFIX
 # define FLOAT_FMT_FLAG
 # define FLOAT_NAME_EXT
-# define NDIGIT_MAX DBL_DIG
+# if DBL_MANT_DIG == 53
+#  define NDIGIT_MAX 17
+# else
+/* See IEEE 854 5.6, table 2 for this formula.  */
+#  define NDIGIT_MAX (lrint (ceil (M_LN2 / M_LN10 * DBL_MANT_DIG + 1.0)))
+# endif
 #endif
 
 #define APPEND(a, b) APPEND2 (a, b)
diff --git a/misc/qefgcvt.c b/misc/qefgcvt.c
index af65fc1688..faf788aa5d 100644
--- a/misc/qefgcvt.c
+++ b/misc/qefgcvt.c
@@ -17,13 +17,20 @@
    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.  */
 
+#include <float.h>
+
 #define FLOAT_TYPE long double
 #define FUNC_PREFIX q
 #define FLOAT_FMT_FLAG "L"
 /* Actually we have to write (LDBL_DIG + log10 (LDBL_MAX_10_EXP)) but
    we don't have log10 available in the preprocessor.  Since we cannot
    assume anything on the used `long double' format be generous.  */
-#define MAXDIG (LDBL_DIG + 12)
-#define NDIGIT_MAX LDBL_DIG
+#define MAXDIG (NDIGIT_MAX + 12)
+#if LDBL_MANT_DIG == 64
+# define NDIGIT_MAX 21
+#else
+/* See IEEE 854 5.6, table 2 for this formula.  */
+# define NDIGIT_MAX (lrint (ceil (M_LN2 / M_LN10 * LDBL_MANT_DIG + 1.0)))
+#endif
 
 #include "efgcvt.c"
diff --git a/misc/qefgcvt_r.c b/misc/qefgcvt_r.c
index 012ab54acc..5ff8110e3b 100644
--- a/misc/qefgcvt_r.c
+++ b/misc/qefgcvt_r.c
@@ -18,10 +18,17 @@
    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.  */
 
+#include <float.h>
+
 #define FLOAT_TYPE long double
 #define FUNC_PREFIX q
 #define FLOAT_FMT_FLAG "L"
 #define FLOAT_NAME_EXT l
-# define NDIGIT_MAX LDBL_DIG
+#if LDBL_MANT_DIG == 64
+# define NDIGIT_MAX 21
+#else
+/* See IEEE 854 5.6, table 2 for this formula.  */
+# define NDIGIT_MAX (lrint (ceil (M_LN2 / M_LN10 * LDBL_MANT_DIG + 1.0)))
+#endif
 
 #include "efgcvt_r.c"
diff --git a/misc/tst-efgcvt.c b/misc/tst-efgcvt.c
index d0ebd0d863..cfbaa21cb1 100644
--- a/misc/tst-efgcvt.c
+++ b/misc/tst-efgcvt.c
@@ -56,7 +56,6 @@ static testcase ecvt_tests[] =
   { 123.01, -4, 3, "" },
   { 126.71, -4, 3, "" },
   { 0.0, 4, 1, "0000" },
-  { 92.0, 16, 2, "920000000000000" },
   /* -1.0 is end marker.  */
   { -1.0, 0, 0, "" }
 };