[PATCH 1/2] mpi/longlong: make use of compiler provided __builtin_ctz/__builtin_clz

[Jussi Kivilinna]

* configure.ac (gcry_cv_have_builtin_ctzl, gcry_cv_have_builtin_clz)
(gcry_cv_have_builtin_clzl): New checks.
* mpi/longlong.h (count_leading_zeros, count_trailing_zeros): Use
__buildin_clz[l]/__builtin_ctz[l] if available and bit counting
macros not yet provided by inline assembly.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna at iki.fi>
---
 configure.ac   | 45 +++++++++++++++++++++++++++++++++++++++++++++
 mpi/longlong.h | 20 ++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/configure.ac b/configure.ac
index fda74056..e0d52d8c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -903,6 +903,51 @@ if test "$gcry_cv_have_builtin_ctz" = "yes" ; then
 fi
 
 
+#
+# Check for __builtin_ctzl intrinsic.
+#
+AC_CACHE_CHECK(for __builtin_ctzl,
+       [gcry_cv_have_builtin_ctzl],
+       [gcry_cv_have_builtin_ctzl=no
+        AC_LINK_IFELSE([AC_LANG_PROGRAM([],
+          [unsigned long x = 0; long y = __builtin_ctzl(x); return y;])],
+          [gcry_cv_have_builtin_ctzl=yes])])
+if test "$gcry_cv_have_builtin_ctzl" = "yes" ; then
+   AC_DEFINE(HAVE_BUILTIN_CTZL, 1,
+             [Defined if compiler has '__builtin_ctzl' intrinsic])
+fi
+
+
+#
+# Check for __builtin_clz intrinsic.
+#
+AC_CACHE_CHECK(for __builtin_clz,
+       [gcry_cv_have_builtin_clz],
+       [gcry_cv_have_builtin_clz=no
+        AC_LINK_IFELSE([AC_LANG_PROGRAM([],
+          [unsigned int x = 0; int y = __builtin_clz(x); return y;])],
+          [gcry_cv_have_builtin_clz=yes])])
+if test "$gcry_cv_have_builtin_clz" = "yes" ; then
+   AC_DEFINE(HAVE_BUILTIN_CLZ, 1,
+             [Defined if compiler has '__builtin_clz' intrinsic])
+fi
+
+
+#
+# Check for __builtin_clzl intrinsic.
+#
+AC_CACHE_CHECK(for __builtin_clzl,
+       [gcry_cv_have_builtin_clzl],
+       [gcry_cv_have_builtin_clzl=no
+        AC_LINK_IFELSE([AC_LANG_PROGRAM([],
+          [unsigned long x = 0; long y = __builtin_clzl(x); return y;])],
+          [gcry_cv_have_builtin_clzl=yes])])
+if test "$gcry_cv_have_builtin_clzl" = "yes" ; then
+   AC_DEFINE(HAVE_BUILTIN_CLZL, 1,
+             [Defined if compiler has '__builtin_clzl' intrinsic])
+fi
+
+
 #
 # Check for __sync_synchronize intrinsic.
 #
diff --git a/mpi/longlong.h b/mpi/longlong.h
index 6573c984..6993d6eb 100644
--- a/mpi/longlong.h
+++ b/mpi/longlong.h
@@ -1681,6 +1681,26 @@ extern USItype __udiv_qrnnd ();
 #  define udiv_qrnnd __udiv_qrnnd_c
 #endif
 
+#if !defined (count_leading_zeros)
+#  if defined (HAVE_BUILTIN_CLZL) && SIZEOF_UNSIGNED_LONG * 8 == W_TYPE_SIZE
+#    define count_leading_zeros(count, x) (count = __builtin_clzl(x))
+#    undef COUNT_LEADING_ZEROS_0 /* Input X=0 is undefined for the builtin. */
+#  elif defined (HAVE_BUILTIN_CLZ) && SIZEOF_UNSIGNED_INT * 8 == W_TYPE_SIZE
+#    define count_leading_zeros(count, x) (count = __builtin_clz(x))
+#    undef COUNT_LEADING_ZEROS_0 /* Input X=0 is undefined for the builtin. */
+#  endif
+#endif
+
+#if !defined (count_trailing_zeros)
+#  if defined (HAVE_BUILTIN_CTZL) && SIZEOF_UNSIGNED_LONG * 8 == W_TYPE_SIZE
+#    define count_trailing_zeros(count, x) (count = __builtin_ctzl(x))
+#    undef COUNT_LEADING_ZEROS_0 /* Input X=0 is undefined for the builtin. */
+#  elif defined (HAVE_BUILTIN_CTZ) && SIZEOF_UNSIGNED_INT * 8 == W_TYPE_SIZE
+#    define count_trailing_zeros(count, x) (count = __builtin_ctz(x))
+#    undef COUNT_LEADING_ZEROS_0 /* Input X=0 is undefined for the builtin. */
+#  endif
+#endif
+
 #if !defined (count_leading_zeros)
 extern
 #  ifdef __STDC__
-- 
2.27.0