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Add, optional, support for 128bit integers.

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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
This commit is contained in:
Andres Freund
2015-03-20 10:26:17 +01:00
parent 7e9ed623d9
commit 8122e1437e
6 changed files with 109 additions and 0 deletions
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37
config/c-compiler.m4
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@ -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
# -----------------------