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Provide overflow safe integer math inline functions.

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It's not easy to get signed integer overflow checks correct and
fast. Therefore abstract the necessary infrastructure into a common
header providing addition, subtraction and multiplication for 16, 32,
64 bit signed integers.

The new macros aren't yet used, but a followup commit will convert
several open coded overflow checks.

Author: Andres Freund, with some code stolen from Greg Stark
Reviewed-By: Robert Haas
Discussion: https://postgr.es/m/20171024103954.ztmatprlglz3rwke@alap3.anarazel.de
This commit is contained in:
Andres Freund
2017-10-29 22:13:54 -07:00
parent 95b52351fe
commit 4d6ad31257
6 changed files with 304 additions and 0 deletions
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22
config/c-compiler.m4
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@ -299,6 +299,28 @@ fi])# PGAC_C_BUILTIN_CONSTANT_P
# PGAC_C_BUILTIN_OP_OVERFLOW
# -------------------------
# Check if the C compiler understands __builtin_$op_overflow(),
# and define HAVE__BUILTIN_OP_OVERFLOW if so.
#
# Check for the most complicated case, 64 bit multiplication, as a
# proxy for all of the operations.
AC_DEFUN([PGAC_C_BUILTIN_OP_OVERFLOW],
[AC_CACHE_CHECK(for __builtin_mul_overflow, pgac_cv__builtin_op_overflow,
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],
[PG_INT64_TYPE result;
__builtin_mul_overflow((PG_INT64_TYPE) 1, (PG_INT64_TYPE) 2, &result);]
)],
[pgac_cv__builtin_op_overflow=yes],
[pgac_cv__builtin_op_overflow=no])])
if test x"$pgac_cv__builtin_op_overflow" = xyes ; then
AC_DEFINE(HAVE__BUILTIN_OP_OVERFLOW, 1,
[Define to 1 if your compiler understands __builtin_$op_overflow.])
fi])# PGAC_C_BUILTIN_OP_OVERFLOW
# PGAC_C_BUILTIN_UNREACHABLE
# --------------------------
# Check if the C compiler understands __builtin_unreachable(),