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# SPDX-License-Identifier: 0BSD
#############################################################################
#
# SYNOPSIS
#
# TUKLIB_INTEGER
#
# DESCRIPTION
#
# Checks for tuklib_integer.h:
# - Endianness
# - Does the compiler or the operating system provide byte swapping macros
# - Does the hardware support fast unaligned access to 16-bit, 32-bit,
# and 64-bit integers
#
#############################################################################
#
# Author: Lasse Collin
#
#############################################################################
AC_DEFUN_ONCE([TUKLIB_INTEGER], [
AC_REQUIRE([TUKLIB_COMMON])
AC_REQUIRE([AC_C_BIGENDIAN])
AC_MSG_CHECKING([if __builtin_bswap16/32/64 are supported])
AC_LINK_IFELSE([AC_LANG_PROGRAM([[]],
[[__builtin_bswap16(1);
__builtin_bswap32(1);
__builtin_bswap64(1);]])],
[
AC_DEFINE([HAVE___BUILTIN_BSWAPXX], [1],
[Define to 1 if the GNU C extensions
__builtin_bswap16/32/64 are supported.])
AC_MSG_RESULT([yes])
], [
AC_MSG_RESULT([no])
# Look for other byteswapping methods.
AC_CHECK_HEADERS([byteswap.h sys/endian.h sys/byteorder.h], [break])
# Even if we have byteswap.h we may lack the specific macros/functions.
if test x$ac_cv_header_byteswap_h = xyes ; then
m4_foreach([FUNC], [bswap_16,bswap_32,bswap_64], [
AC_MSG_CHECKING([if FUNC is available])
AC_LINK_IFELSE([AC_LANG_SOURCE([
#include <byteswap.h>
int
main(void)
{
FUNC[](42);
return 0;
}
])], [
AC_DEFINE(HAVE_[]m4_toupper(FUNC), [1],
[Define to 1 if] FUNC [is available.])
AC_MSG_RESULT([yes])
], [AC_MSG_RESULT([no])])
])dnl
fi
])
AC_MSG_CHECKING([if unaligned memory access should be used])
AC_ARG_ENABLE([unaligned-access], AS_HELP_STRING([--enable-unaligned-access],
[Enable if the system supports *fast* unaligned memory access
with 16-bit, 32-bit, and 64-bit integers. By default,
this is enabled on x86, x86-64,
32/64-bit big endian PowerPC,
64-bit little endian PowerPC,
and some ARM, ARM64, and RISC-V systems.]),
[], [enable_unaligned_access=auto])
if test "x$enable_unaligned_access" = xauto ; then
# NOTE: There might be other architectures on which unaligned access
# is fast.
case $host_cpu in
i?86|x86_64|powerpc|powerpc64|powerpc64le)
enable_unaligned_access=yes
;;
arm*|aarch64*|riscv*)
# On 32-bit and 64-bit ARM, GCC and Clang
# #define __ARM_FEATURE_UNALIGNED if
# unaligned access is supported.
#
# Exception: GCC at least up to 13.2.0
# defines it even when using -mstrict-align
# so in that case this autodetection goes wrong.
# Most of the time -mstrict-align isn't used so it
# shouldn't be a common problem in practice. See:
# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111555
#
# RISC-V C API Specification says that if
# __riscv_misaligned_fast is defined then
# unaligned access is known to be fast.
#
# MSVC is handled as a special case: We assume that
# 32/64-bit ARM supports fast unaligned access.
# If MSVC gets RISC-V support then this will assume
# fast unaligned access on RISC-V too.
AC_COMPILE_IFELSE([AC_LANG_SOURCE([
#if !defined(__ARM_FEATURE_UNALIGNED) \
&& !defined(__riscv_misaligned_fast) \
&& !defined(_MSC_VER)
compile error
#endif
int main(void) { return 0; }
])], [enable_unaligned_access=yes], [enable_unaligned_access=no])
;;
*)
enable_unaligned_access=no
;;
esac
fi
if test "x$enable_unaligned_access" = xyes ; then
AC_DEFINE([TUKLIB_FAST_UNALIGNED_ACCESS], [1], [Define to 1 if
the system supports fast unaligned access to 16-bit,
32-bit, and 64-bit integers.])
AC_MSG_RESULT([yes])
else
AC_MSG_RESULT([no])
fi
AC_MSG_CHECKING([if unsafe type punning should be used])
AC_ARG_ENABLE([unsafe-type-punning],
AS_HELP_STRING([--enable-unsafe-type-punning],
[This introduces strict aliasing violations and may result
in broken code. However, this might improve performance in
some cases, especially with old compilers (e.g.
GCC 3 and early 4.x on x86, GCC < 6 on ARMv6 and ARMv7).]),
[], [enable_unsafe_type_punning=no])
if test "x$enable_unsafe_type_punning" = xyes ; then
AC_DEFINE([TUKLIB_USE_UNSAFE_TYPE_PUNNING], [1], [Define to 1 to use
unsafe type punning, e.g. char *x = ...; *(int *)x = 123;
which violates strict aliasing rules and thus is
undefined behavior and might result in broken code.])
AC_MSG_RESULT([yes])
else
AC_MSG_RESULT([no])
fi
AC_MSG_CHECKING([if __builtin_assume_aligned is supported])
AC_LINK_IFELSE([AC_LANG_PROGRAM([[]], [[__builtin_assume_aligned("", 1);]])],
[
AC_DEFINE([HAVE___BUILTIN_ASSUME_ALIGNED], [1],
[Define to 1 if the GNU C extension
__builtin_assume_aligned is supported.])
AC_MSG_RESULT([yes])
], [
AC_MSG_RESULT([no])
])
])dnl
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