diff --git a/aclocal/ax_signed_right_shift.m4 b/aclocal/ax_signed_right_shift.m4
new file mode 100644
index 0000000..0195233
--- /dev/null
+++ b/aclocal/ax_signed_right_shift.m4
@@ -0,0 +1,127 @@
+dnl @synopsis AX_SIGNED_RIGHT_SHIFT
+dnl
+dnl Tests the behavior of a right shift on a negative signed int.
+dnl
+dnl This macro calls:
+dnl   AC_DEFINE(SIGNED_RIGHT_SHIFT_IS)
+dnl   AC_DEFINE(ARITHMETIC_RIGHT_SHIFT)
+dnl   AC_DEFINE(LOGICAL_RIGHT_SHIFT)
+dnl   AC_DEFINE(UNKNOWN_RIGHT_SHIFT)
+dnl
+dnl SIGNED_RIGHT_SHIFT_IS will be equal to one of the other macros.
+dnl It also leaves the shell variables "ax_signed_right_shift"
+dnl set to "arithmetic", "logical", or "unknown".
+dnl
+dnl NOTE: This macro does not work for cross-compiling.
+dnl
+dnl @category C
+dnl @version 2009-03-25
+dnl @license AllPermissive
+dnl
+dnl Copyright (C) 2009 David Reiss
+dnl Copying and distribution of this file, with or without modification,
+dnl are permitted in any medium without royalty provided the copyright
+dnl notice and this notice are preserved.
+
+AC_DEFUN([AX_SIGNED_RIGHT_SHIFT],
+         [
+
+          AC_MSG_CHECKING(the behavior of a signed right shift)
+
+          success_arithmetic=no
+          AC_RUN_IFELSE([AC_LANG_PROGRAM([[]], [[
+          return
+            /* 0xffffffff */
+            -1 >>  1 != -1 ||
+            -1 >>  2 != -1 ||
+            -1 >>  3 != -1 ||
+            -1 >>  4 != -1 ||
+            -1 >>  8 != -1 ||
+            -1 >> 16 != -1 ||
+            -1 >> 24 != -1 ||
+            -1 >> 31 != -1 ||
+            /* 0x80000000 */
+            (-2147483647 - 1) >>  1 != -1073741824 ||
+            (-2147483647 - 1) >>  2 != -536870912  ||
+            (-2147483647 - 1) >>  3 != -268435456  ||
+            (-2147483647 - 1) >>  4 != -134217728  ||
+            (-2147483647 - 1) >>  8 != -8388608    ||
+            (-2147483647 - 1) >> 16 != -32768      ||
+            (-2147483647 - 1) >> 24 != -128        ||
+            (-2147483647 - 1) >> 31 != -1          ||
+            /* 0x90800000 */
+            -1870659584 >>  1 != -935329792 ||
+            -1870659584 >>  2 != -467664896 ||
+            -1870659584 >>  3 != -233832448 ||
+            -1870659584 >>  4 != -116916224 ||
+            -1870659584 >>  8 != -7307264   ||
+            -1870659584 >> 16 != -28544     ||
+            -1870659584 >> 24 != -112       ||
+            -1870659584 >> 31 != -1         ||
+            0;
+          ]])], [
+          success_arithmetic=yes
+          ])
+
+
+          success_logical=no
+          AC_RUN_IFELSE([AC_LANG_PROGRAM([[]], [[
+          return
+            /* 0xffffffff */
+            -1 >>  1 != (signed)((unsigned)-1 >>  1) ||
+            -1 >>  2 != (signed)((unsigned)-1 >>  2) ||
+            -1 >>  3 != (signed)((unsigned)-1 >>  3) ||
+            -1 >>  4 != (signed)((unsigned)-1 >>  4) ||
+            -1 >>  8 != (signed)((unsigned)-1 >>  8) ||
+            -1 >> 16 != (signed)((unsigned)-1 >> 16) ||
+            -1 >> 24 != (signed)((unsigned)-1 >> 24) ||
+            -1 >> 31 != (signed)((unsigned)-1 >> 31) ||
+            /* 0x80000000 */
+            (-2147483647 - 1) >>  1 != (signed)((unsigned)(-2147483647 - 1) >>  1) ||
+            (-2147483647 - 1) >>  2 != (signed)((unsigned)(-2147483647 - 1) >>  2) ||
+            (-2147483647 - 1) >>  3 != (signed)((unsigned)(-2147483647 - 1) >>  3) ||
+            (-2147483647 - 1) >>  4 != (signed)((unsigned)(-2147483647 - 1) >>  4) ||
+            (-2147483647 - 1) >>  8 != (signed)((unsigned)(-2147483647 - 1) >>  8) ||
+            (-2147483647 - 1) >> 16 != (signed)((unsigned)(-2147483647 - 1) >> 16) ||
+            (-2147483647 - 1) >> 24 != (signed)((unsigned)(-2147483647 - 1) >> 24) ||
+            (-2147483647 - 1) >> 31 != (signed)((unsigned)(-2147483647 - 1) >> 31) ||
+            /* 0x90800000 */
+            -1870659584 >>  1 != (signed)((unsigned)-1870659584 >>  1) ||
+            -1870659584 >>  2 != (signed)((unsigned)-1870659584 >>  2) ||
+            -1870659584 >>  3 != (signed)((unsigned)-1870659584 >>  3) ||
+            -1870659584 >>  4 != (signed)((unsigned)-1870659584 >>  4) ||
+            -1870659584 >>  8 != (signed)((unsigned)-1870659584 >>  8) ||
+            -1870659584 >> 16 != (signed)((unsigned)-1870659584 >> 16) ||
+            -1870659584 >> 24 != (signed)((unsigned)-1870659584 >> 24) ||
+            -1870659584 >> 31 != (signed)((unsigned)-1870659584 >> 31) ||
+            0;
+          ]])], [
+          success_logical=yes
+          ])
+
+
+          AC_DEFINE([ARITHMETIC_RIGHT_SHIFT], 1, [Possible value for SIGNED_RIGHT_SHIFT_IS])
+          AC_DEFINE([LOGICAL_RIGHT_SHIFT], 2, [Possible value for SIGNED_RIGHT_SHIFT_IS])
+          AC_DEFINE([UNKNOWN_RIGHT_SHIFT], 3, [Possible value for SIGNED_RIGHT_SHIFT_IS])
+
+          if test "$success_arithmetic" = "yes" && test "$success_logica" = "yes" ; then
+            AC_MSG_ERROR("Right shift appears to be both arithmetic and logical!")
+          elif test "$success_arithmetic" = "yes" ; then
+            ax_signed_right_shift=arithmetic
+            AC_DEFINE([SIGNED_RIGHT_SHIFT_IS], 1,
+                      [Indicates the effect of the right shift operator
+                       on negative signed integers])
+          elif test "$success_logical" = "yes" ; then
+            ax_signed_right_shift=logical
+            AC_DEFINE([SIGNED_RIGHT_SHIFT_IS], 2,
+                      [Indicates the effect of the right shift operator
+                       on negative signed integers])
+          else
+            ax_signed_right_shift=unknown
+            AC_DEFINE([SIGNED_RIGHT_SHIFT_IS], 3,
+                      [Indicates the effect of the right shift operator
+                       on negative signed integers])
+          fi
+
+          AC_MSG_RESULT($ax_signed_right_shift)
+         ])