Add, optional, support for 128bit integers.

We will, for the foreseeable future, not expose 128 bit datatypes to
SQL. But being able to use 128bit math will allow us, in a later patch,
to use 128bit accumulators for some aggregates; leading to noticeable
speedups over using numeric.

So far we only detect a gcc/clang extension that supports 128bit math,
but no 128bit literals, and no *printf support. We might want to expand
this in the future to further compilers; if there are any that that
provide similar support.

Discussion: 544BB5F1.50709@proxel.se
Author: Andreas Karlsson, with significant editorializing by me
Reviewed-By: Peter Geoghegan, Oskari Saarenmaa

config/c-compiler.m4

@@ -125,6 +125,43 @@ undefine([Ac_cachevar])dnl
 ])# PGAC_TYPE_64BIT_INT
 
 
+# PGAC_TYPE_128BIT_INT
+# ---------------------
+# Check if __int128 is a working 128 bit integer type, and if so
+# define PG_INT128_TYPE to that typename.  This currently only detects
+# a GCC/clang extension, but support for different environments may be
+# added in the future.
+#
+# For the moment we only test for support for 128bit math; support for
+# 128bit literals and snprintf is not required.
+AC_DEFUN([PGAC_TYPE_128BIT_INT],
+[AC_CACHE_CHECK([for __int128], [pgac_cv__128bit_int],
+[AC_LINK_IFELSE([AC_LANG_PROGRAM([
+/*
+ * These are globals to discourage the compiler from folding all the
+ * arithmetic tests down to compile-time constants.  We do not have
+ * convenient support for 64bit literals at this point...
+ */
+__int128 a = 48828125;
+__int128 b = 97656255;
+],[
+__int128 c,d;
+a = (a << 12) + 1; /* 200000000001 */
+b = (b << 12) + 5; /* 400000000005 */
+/* use the most relevant arithmetic ops */
+c = a * b;
+d = (c + b) / b;
+/* return different values, to prevent optimizations */
+if (d != a+1)
+  return 0;
+return 1;
+])],
+[pgac_cv__128bit_int=yes],
+[pgac_cv__128bit_int=no])])
+if test x"$pgac_cv__128bit_int" = xyes ; then
+  AC_DEFINE(PG_INT128_TYPE, __int128, [Define to the name of a signed 128-bit integer type.])
+fi])# PGAC_TYPE_128BIT_INT
+
 
 # PGAC_C_FUNCNAME_SUPPORT
 # -----------------------

configure

@@ -13803,6 +13803,58 @@ _ACEOF
 fi
 
 
+# Check for extensions offering the integer scalar type __int128.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __int128" >&5
+$as_echo_n "checking for __int128... " >&6; }
+if ${pgac_cv__128bit_int+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+/*
+ * These are globals to discourage the compiler from folding all the
+ * arithmetic tests down to compile-time constants.  We do not have
+ * convenient support for 64bit literals at this point...
+ */
+__int128 a = 48828125;
+__int128 b = 97656255;
+
+int
+main ()
+{
+
+__int128 c,d;
+a = (a << 12) + 1; /* 200000000001 */
+b = (b << 12) + 5; /* 400000000005 */
+/* use the most relevant arithmetic ops */
+c = a * b;
+d = (c + b) / b;
+/* return different values, to prevent optimizations */
+if (d != a+1)
+  return 0;
+return 1;
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  pgac_cv__128bit_int=yes
+else
+  pgac_cv__128bit_int=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv__128bit_int" >&5
+$as_echo "$pgac_cv__128bit_int" >&6; }
+if test x"$pgac_cv__128bit_int" = xyes ; then
+
+$as_echo "#define PG_INT128_TYPE __int128" >>confdefs.h
+
+fi
+
 # Check for various atomic operations now that we have checked how to declare
 # 64bit integers.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for builtin __sync char locking functions" >&5

configure.in

@@ -1771,6 +1771,9 @@ AC_CHECK_TYPES([int8, uint8, int64, uint64], [], [],
 # C, but is missing on some old platforms.
 AC_CHECK_TYPES(sig_atomic_t, [], [], [#include <signal.h>])
 
+# Check for extensions offering the integer scalar type __int128.
+PGAC_TYPE_128BIT_INT
+
 # Check for various atomic operations now that we have checked how to declare
 # 64bit integers.
 PGAC_HAVE_GCC__SYNC_CHAR_TAS

src/include/c.h

@@ -293,6 +293,17 @@ typedef unsigned long long int uint64;
 #define HAVE_INT64_TIMESTAMP
 #endif
 
+/*
+ * 128-bit signed and unsigned integers
+ *		There currently is only a limited support for the type. E.g. 128bit
+ *		literals and snprintf are not supported; but math is.
+ */
+#if defined(PG_INT128_TYPE)
+#define HAVE_INT128
+typedef PG_INT128_TYPE int128;
+typedef unsigned PG_INT128_TYPE uint128;
+#endif
+
 /* sig_atomic_t is required by ANSI C, but may be missing on old platforms */
 #ifndef HAVE_SIG_ATOMIC_T
 typedef int sig_atomic_t;

src/include/pg_config.h.in

@@ -711,6 +711,9 @@
 /* Define to the version of this package. */
 #undef PACKAGE_VERSION
 
+/* Define to the name of a signed 128-bit integer type. */
+#undef PG_INT128_TYPE
+
 /* Define to the name of a signed 64-bit integer type. */
 #undef PG_INT64_TYPE
 

src/include/pg_config.h.win32

@@ -562,6 +562,9 @@
 /* Define to the version of this package. */
 #define PACKAGE_VERSION "9.5devel"
 
+/* Define to the name of a signed 128-bit integer type. */
+#undef PG_INT128_TYPE
+
 /* Define to the name of a signed 64-bit integer type. */
 #define PG_INT64_TYPE long long int