--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,21 @@
+2012-03-03  Bruno Haible  <bruno@clisp.org>
+
+	modf* tests: More tests.
+	* tests/test-modf.h: New file.
+	* tests/test-modf.c: Include <float.h> and test-modf.h.
+	(main): Invoke test_function.
+	* tests/test-modff.c: Include <float.h> and test-modf.h.
+	(main): Invoke test_function.
+	* tests/test-modfl.c: Include <float.h> and test-modf.h.
+	(main): Invoke test_function.
+	* modules/modf-tests (Files): Add tests/test-modf.h, tests/randomd.c.
+	(Makefile.am): Add randomd.c to test_modf_SOURCES.
+	* modules/modff-tests (Files): Add tests/test-modf.h, tests/randomf.c.
+	(Makefile.am): Add randomf.c to test_modff_SOURCES.
+	* modules/modfl-tests (Files): Add tests/test-modf.h, tests/randoml.c.
+	(Depends-on): Add 'float'.
+	(Makefile.am): Add randoml.c to test_modfl_SOURCES.
+
 2012-03-03  Bruno Haible  <bruno@clisp.org>
 
 	fabs* tests: More tests.

--- a/modules/modf-tests
+++ b/modules/modf-tests
@@ -1,7 +1,9 @@
 Files:
 tests/test-modf.c
+tests/test-modf.h
 tests/signature.h
 tests/macros.h
+tests/randomd.c
 
 Depends-on:
 
@@ -10,4 +12,5 @@
 Makefile.am:
 TESTS += test-modf
 check_PROGRAMS += test-modf
+test_modf_SOURCES = test-modf.c randomd.c
 test_modf_LDADD = $(LDADD) @MODF_LIBM@

--- a/modules/modff-tests
+++ b/modules/modff-tests
@@ -1,7 +1,9 @@
 Files:
 tests/test-modff.c
+tests/test-modf.h
 tests/signature.h
 tests/macros.h
+tests/randomf.c
 
 Depends-on:
 
@@ -10,4 +12,5 @@
 Makefile.am:
 TESTS += test-modff
 check_PROGRAMS += test-modff
+test_modff_SOURCES = test-modff.c randomf.c
 test_modff_LDADD = $(LDADD) @MODFF_LIBM@

--- a/modules/modfl-tests
+++ b/modules/modfl-tests
@@ -1,14 +1,18 @@
 Files:
 tests/test-modfl.c
+tests/test-modf.h
 tests/signature.h
 tests/macros.h
+tests/randoml.c
 
 Depends-on:
 fpucw
+float
 
 configure.ac:
 
 Makefile.am:
 TESTS += test-modfl
 check_PROGRAMS += test-modfl
+test_modfl_SOURCES = test-modfl.c randoml.c
 test_modfl_LDADD = $(LDADD) @MODFL_LIBM@

--- a/tests/test-modf.c
+++ b/tests/test-modf.c
@@ -23,11 +23,16 @@
 #include "signature.h"
 SIGNATURE_CHECK (modf, double, (double, double *));
 
+#include <float.h>
+
 #include "macros.h"
 
-volatile double x;
-double y;
-double z;
+#define DOUBLE double
+#define L_(literal) literal
+#define MANT_DIG DBL_MANT_DIG
+#define MODF modf
+#define RANDOM randomd
+#include "test-modf.h"
 
 int
 main ()
@@ -44,5 +49,7 @@
   ASSERT (y >= -0.972406761 && y <= -0.972406759);
   ASSERT (z == -5.0);
 
+  test_function ();
+
   return 0;
 }

new file mode 100644
--- /dev/null
+++ b/tests/test-modf.h
@@ -0,0 +1,62 @@
+/* Test of modf*() function family.
+   Copyright (C) 2012 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+static void
+test_function (void)
+{
+  int i;
+  const DOUBLE TWO_MANT_DIG =
+    /* Assume MANT_DIG <= 5 * 31.
+       Use the identity
+         n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5).  */
+    (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
+    * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
+    * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
+    * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
+    * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
+
+  /* Randomized tests.  */
+  for (i = 0; i < SIZEOF (RANDOM); i++)
+    {
+      DOUBLE x = RANDOM[i]; /* 0.0 <= x < 1.0 */
+      DOUBLE y;
+      DOUBLE z;
+
+      y = MODF (x, &z);
+      ASSERT (z == L_(0.0));
+      ASSERT (y == x);
+
+      y = MODF (- x, &z);
+      ASSERT (z == L_(0.0));
+      ASSERT (y == - x);
+
+      y = MODF (L_(1.0) + x, &z);
+      ASSERT (z == L_(1.0));
+      y -= x;
+      ASSERT (y >= - L_(1.0) / TWO_MANT_DIG);
+      ASSERT (y <= L_(1.0) / TWO_MANT_DIG);
+
+      y = MODF (- L_(1.0) - x, &z);
+      ASSERT (z == - L_(1.0));
+      y -= - x;
+      ASSERT (y >= - L_(1.0) / TWO_MANT_DIG);
+      ASSERT (y <= L_(1.0) / TWO_MANT_DIG);
+    }
+}
+
+volatile DOUBLE x;
+DOUBLE y;
+DOUBLE z;

--- a/tests/test-modff.c
+++ b/tests/test-modff.c
@@ -23,11 +23,16 @@
 #include "signature.h"
 SIGNATURE_CHECK (modff, float, (float, float *));
 
+#include <float.h>
+
 #include "macros.h"
 
-volatile float x;
-float y;
-float z;
+#define DOUBLE float
+#define L_(literal) literal##f
+#define MANT_DIG FLT_MANT_DIG
+#define MODF modff
+#define RANDOM randomf
+#include "test-modf.h"
 
 int
 main ()
@@ -44,5 +49,7 @@
   ASSERT (y >= -0.972408f && y <= -0.972406f);
   ASSERT (z == -5.0f);
 
+  test_function ();
+
   return 0;
 }

--- a/tests/test-modfl.c
+++ b/tests/test-modfl.c
@@ -23,12 +23,17 @@
 #include "signature.h"
 SIGNATURE_CHECK (modfl, long double, (long double, long double *));
 
+#include <float.h>
+
 #include "fpucw.h"
 #include "macros.h"
 
-volatile long double x;
-long double y;
-long double z;
+#define DOUBLE long double
+#define L_(literal) literal##L
+#define MANT_DIG LDBL_MANT_DIG
+#define MODF modfl
+#define RANDOM randoml
+#include "test-modf.h"
 
 int
 main ()
@@ -49,5 +54,7 @@
   ASSERT (y >= -0.972406761L && y <= -0.972406759L);
   ASSERT (z == -5.0L);
 
+  test_function ();
+
   return 0;
 }