--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2012-04-03  Bruno Haible  <bruno@clisp.org>
 
+	Tests for module 'ilogb'.
+	* modules/ilogb-tests: New file.
+	* tests/test-ilogb.c: New file.
+	* tests/test-ilogb.h: New file, based on tests/test-logb.h and
+	tests/test-logb-ieee.h.
+
 	New module 'ilogb'.
 	* lib/math.in.h (ilogb): New declaration.
 	* lib/ilogb.c: New file.

new file mode 100644
--- /dev/null
+++ b/modules/ilogb-tests
@@ -0,0 +1,19 @@
+Files:
+tests/test-ilogb.c
+tests/test-ilogb.h
+tests/minus-zero.h
+tests/infinity.h
+tests/nan.h
+tests/signature.h
+tests/macros.h
+tests/randomd.c
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-ilogb
+check_PROGRAMS += test-ilogb
+test_ilogb_SOURCES = test-ilogb.c randomd.c
+test_ilogb_LDADD = $(LDADD) @ILOGB_LIBM@

new file mode 100644
--- /dev/null
+++ b/tests/test-ilogb.c
@@ -0,0 +1,61 @@
+/* Test of ilogb() function.
+   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/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2012.  */
+
+#include <config.h>
+
+#include <math.h>
+
+#include "signature.h"
+SIGNATURE_CHECK (ilogb, int, (double));
+
+#include <float.h>
+#include <limits.h>
+
+#include "minus-zero.h"
+#include "infinity.h"
+#include "nan.h"
+#include "macros.h"
+
+#undef INFINITY
+#undef NAN
+
+#define DOUBLE double
+/* The use of 'volatile' guarantees that excess precision bits are dropped
+   when dealing with denormalized numbers.  It is necessary on x86 systems
+   where double-floats are not IEEE compliant by default, to avoid that the
+   results become platform and compiler option dependent.  'volatile' is a
+   portable alternative to gcc's -ffloat-store option.  */
+#define VOLATILE volatile
+#define INFINITY Infinityd ()
+#define NAN NaNd ()
+#define L_(literal) literal
+#define MINUS_ZERO minus_zerod
+#define MAX_EXP DBL_MAX_EXP
+#define MIN_EXP DBL_MIN_EXP
+#define MIN_NORMAL_EXP DBL_MIN_EXP
+#define ILOGB ilogb
+#define RANDOM randomd
+#include "test-ilogb.h"
+
+int
+main ()
+{
+  test_function ();
+
+  return 0;
+}

new file mode 100644
--- /dev/null
+++ b/tests/test-ilogb.h
@@ -0,0 +1,151 @@
+/* Test of ilogb*() 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 DOUBLE
+my_ldexp (DOUBLE x, int d)
+{
+  for (; d > 0; d--)
+    x *= L_(2.0);
+  for (; d < 0; d++)
+    x *= L_(0.5);
+  return x;
+}
+
+static void
+test_function (void)
+{
+  int i;
+  VOLATILE DOUBLE x;
+  int y;
+
+  /* Some particular values.  */
+  x = L_(0.6);
+  y = ILOGB (x);
+  ASSERT (y == -1);
+
+  x = L_(1.2);
+  y = ILOGB (x);
+  ASSERT (y == 0);
+
+  x = L_(2.1);
+  y = ILOGB (x);
+  ASSERT (y == 1);
+
+  x = L_(3.9);
+  y = ILOGB (x);
+  ASSERT (y == 1);
+
+  x = L_(4.0);
+  y = ILOGB (x);
+  ASSERT (y == (FLT_RADIX == 2 ? 2 : 1));
+
+  x = L_(0.25);
+  y = ILOGB (x);
+  ASSERT (y == (FLT_RADIX == 2 ? -2 : -1));
+
+  /* Zero.  */
+  ASSERT (ILOGB (L_(0.0)) == FP_ILOGB0);
+  ASSERT (ILOGB (MINUS_ZERO) == FP_ILOGB0);
+
+  /* Infinity.  */
+  ASSERT (ILOGB (INFINITY) == INT_MAX);
+  ASSERT (ILOGB (- INFINITY) == INT_MAX);
+
+  /* NaN.  */
+  ASSERT (ILOGB (NAN) == FP_ILOGBNAN);
+
+  /* From here on, this test assumes FLT_RADIX == 2.  */
+
+  for (i = 1, x = L_(1.0); i <= MAX_EXP; i++, x *= L_(2.0))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+  for (i = 1, x = L_(1.0); i >= MIN_NORMAL_EXP; i--, x *= L_(0.5))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+  for (; i >= MIN_EXP - 100 && x > L_(0.0); i--, x *= L_(0.5))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+
+  for (i = 1, x = - L_(1.0); i <= MAX_EXP; i++, x *= L_(2.0))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+  for (i = 1, x = - L_(1.0); i >= MIN_NORMAL_EXP; i--, x *= L_(0.5))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+  for (; i >= MIN_EXP - 100 && x < L_(0.0); i--, x *= L_(0.5))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+
+  for (i = 1, x = L_(1.01); i <= MAX_EXP; i++, x *= L_(2.0))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+  for (i = 1, x = L_(1.01); i >= MIN_NORMAL_EXP; i--, x *= L_(0.5))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+  for (; i >= MIN_EXP - 100 && x > L_(0.0); i--, x *= L_(0.5))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+
+  for (i = 1, x = L_(1.73205); i <= MAX_EXP; i++, x *= L_(2.0))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+  for (i = 1, x = L_(1.73205); i >= MIN_NORMAL_EXP; i--, x *= L_(0.5))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1);
+    }
+  for (; i >= MIN_EXP - 100 && x > L_(0.0); i--, x *= L_(0.5))
+    {
+      y = ILOGB (x);
+      ASSERT (y == i - 1 || y == i);
+    }
+
+  /* Randomized tests.  */
+  for (i = 0; i < SIZEOF (RANDOM); i++)
+    {
+      x = L_(20.0) * RANDOM[i] - L_(10.0); /* -10.0 <= x <= 10.0 */
+      if (x != L_(0.0))
+        {
+          DOUBLE abs_x = (x < L_(0.0) ? - x : x);
+          y = ILOGB (x);
+          ASSERT (abs_x >= my_ldexp (L_(1.0), y));
+          ASSERT (abs_x < my_ldexp (L_(1.0), y + 1));
+        }
+    }
+}
+
+volatile DOUBLE x;
+DOUBLE y;