3 files changed, 44 insertions, 1 deletions
diff --git a/gcc/c-family/c-cppbuiltin.cc b/gcc/c-family/c-cppbuiltin.cc
index d4de5a0..4b8486c 100644
--- a/gcc/c-family/c-cppbuiltin.cc
+++ b/gcc/c-family/c-cppbuiltin.cc
@@ -279,7 +279,7 @@ builtin_define_float_constants (const char *name_prefix,
   /* The difference between 1 and the least value greater than 1 that is
      representable in the given floating point type, b**(1-p).  */
   sprintf (name, "__%s_EPSILON__", name_prefix);
-  if (fmt->pnan < fmt->p)
+  if (fmt->pnan < fmt->p && (c_dialect_cxx () || !flag_isoc2x))
     /* This is an IBM extended double format, so 1.0 + any double is
        representable precisely.  */
       sprintf (buf, "0x1p%d", fmt->emin - fmt->p);
diff --git a/gcc/testsuite/gcc.dg/c11-float-7.c b/gcc/testsuite/gcc.dg/c11-float-7.c
new file mode 100644
index 0000000..a8a7ef5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c11-float-7.c
@@ -0,0 +1,24 @@
+/* Test C11 definition of LDBL_EPSILON.  Based on
+   gcc.target/powerpc/rs6000-ldouble-2.c.  */
+/* { dg-do run } */
+/* { dg-options "-std=c11 -pedantic-errors" } */
+
+#include <float.h>
+
+extern void abort (void);
+extern void exit (int);
+
+int
+main (void)
+{
+  volatile long double ee = 1.0;
+  long double eps = ee;
+  while (ee + 1.0 != 1.0)
+    {
+      eps = ee;
+      ee = eps / 2;
+    }
+  if (eps != LDBL_EPSILON)
+    abort ();
+  exit (0);
+}
diff --git a/gcc/testsuite/gcc.dg/c2x-float-12.c b/gcc/testsuite/gcc.dg/c2x-float-12.c
new file mode 100644
index 0000000..40900bd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c2x-float-12.c
@@ -0,0 +1,19 @@
+/* Test C2x definition of LDBL_EPSILON.  */
+/* { dg-do run } */
+/* { dg-options "-std=c2x -pedantic-errors" } */
+
+#include <float.h>
+
+extern void abort (void);
+extern void exit (int);
+
+int
+main (void)
+{
+  volatile long double x = 1.0L;
+  for (int i = 0; i < LDBL_MANT_DIG - 1; i++)
+    x /= 2;
+  if (x != LDBL_EPSILON)
+    abort ();
+  exit (0);
+}