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|
# malloc-align.m4 serial 1
dnl Copyright (C) 2020-2023 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
dnl Defines a C macro MALLOC_ALIGNMENT, whose value is a numeric constant,
dnl a power of 2, with the property that
dnl (uintptr_t) malloc (N)
dnl is always guaranteed to be a multiple of MALLOC_ALIGNMENT.
AC_DEFUN([gl_MALLOC_ALIGNMENT],
[
AC_REQUIRE([AC_CANONICAL_HOST])
AC_CACHE_CHECK([for the malloc() alignment],
[gl_cv_malloc_alignment],
[gl_cv_malloc_alignment=
AC_RUN_IFELSE(
[AC_LANG_PROGRAM(
[[#include <stdio.h>
#include <stdlib.h>
#if defined _WIN32 && !defined __CYGWIN__
# include <inttypes.h>
/* uintptr_t is equivalent to 'unsigned long long' if _WIN64,
or to 'unsigned long' otherwise. */
#else
# undef uintptr_t
# define uintptr_t unsigned long
#endif
]],
[[FILE *fp = fopen ("conftest.out", "w");
if (fp == NULL)
return 1;
{
uintptr_t bits = 0;
bits |= (uintptr_t) malloc (1);
bits |= (uintptr_t) malloc (1);
bits |= (uintptr_t) malloc (1);
bits |= (uintptr_t) malloc (2);
bits |= (uintptr_t) malloc (2);
bits |= (uintptr_t) malloc (2);
bits |= (uintptr_t) malloc (3);
bits |= (uintptr_t) malloc (3);
bits |= (uintptr_t) malloc (3);
bits |= (uintptr_t) malloc (5);
bits |= (uintptr_t) malloc (8);
bits |= (uintptr_t) malloc (8);
bits |= (uintptr_t) malloc (13);
bits |= (uintptr_t) malloc (13);
bits |= (uintptr_t) malloc (19);
bits |= (uintptr_t) malloc (19);
bits |= (uintptr_t) malloc (28);
bits |= (uintptr_t) malloc (28);
bits |= (uintptr_t) malloc (37);
bits |= (uintptr_t) malloc (37);
bits |= (uintptr_t) malloc (73);
bits |= (uintptr_t) malloc (73);
bits |= (uintptr_t) malloc (117);
bits |= (uintptr_t) malloc (117);
bits |= (uintptr_t) malloc (351);
bits |= (uintptr_t) malloc (351);
bits |= (uintptr_t) malloc (914);
bits |= (uintptr_t) malloc (914);
bits |= (uintptr_t) malloc (1712);
bits |= (uintptr_t) malloc (1712);
bits |= (uintptr_t) malloc (4021);
bits |= (uintptr_t) malloc (4021);
bits |= (uintptr_t) malloc (7641);
bits |= (uintptr_t) malloc (7641);
bits |= (uintptr_t) malloc (17027);
bits |= (uintptr_t) malloc (17027);
bits |= (uintptr_t) malloc (81231);
bits |= (uintptr_t) malloc (81231);
fprintf (fp, "%u\n", (unsigned int) (((bits ^ (bits - 1)) + 1) >> 1));
}
if (fclose (fp) != 0)
return 2;
return 0;
]])
],
[gl_cv_malloc_alignment=`cat conftest.out`],
[gl_cv_malloc_alignment="unknown"],
[dnl When cross-compiling, guess a value. Note that it's OK to return
dnl a smaller value (e.g. 4 instead of 8 or 16).
gl_cv_malloc_alignment="unknown"
case "$host_os" in
linux* | mingw*)
dnl On Linux:
dnl - It's 8 on most 32-bit platforms, except 16 on x86_64-x32 and
dnl (with newer versions of glibc) on i386 and powerpc. 8 is a
dnl safe guess.
dnl - It's 16 on all 64-bit platforms.
dnl On Windows: It's 8 on 32-bit Windows, 16 on 64-bit Windows.
for nn in 4 8 16 32; do
AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM([[
#define MALLOC_ALIGN (2 * sizeof (void *))
int test [MALLOC_ALIGN <= $nn ? 1 : -1];
]])
],
[gl_cv_malloc_alignment="guessing $nn"
break
],
[:])
done
;;
*)
dnl If we don't know, assume the worst.
dnl This minimum is e.g. reached on NetBSD/i386 and NetBSD/sparc.
for nn in 4 8 16; do
AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM([[
#define MALLOC_ALIGN (sizeof (void *))
int test [MALLOC_ALIGN <= $nn ? 1 : -1];
]])
],
[gl_cv_malloc_alignment="guessing $nn"
break
],
[:])
done
;;
esac
])
])
case "$gl_cv_malloc_alignment" in
"unknown")
dnl Assume the worst.
value=4
;;
"guessing "*)
value=`echo "$gl_cv_malloc_alignment" | sed -e 's/guessing //'`
;;
*)
value="$gl_cv_malloc_alignment"
;;
esac
AC_DEFINE_UNQUOTED([MALLOC_ALIGNMENT], [$value],
[Define to the guaranteed alignment of malloc() return values.])
])
|
