kc3-lang/gnulib/m4/atomic-cas.m4

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• Hash : b744688d
  Author :
  Date : 2024-04-04T11:16:15
  

  Make the serial numbers in *.m4 files effective.
  
  Reported by Sam James in
  <https://lists.gnu.org/archive/html/bug-gnulib/2024-04/msg00051.html>.
  
  * m4/*.m4: Apply sed -e '1s|^# \(.*[.]m4\) serial |# \1\n# serial |'.
  

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• m4/atomic-cas.m4

• # atomic-cas.m4
  # serial 1
  dnl Copyright (C) 2024 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.
  
  # Determines whether the atomic compare-and-swap operations, officially
  # supported in GCC >= 4.1 and clang >= 3.0, are actually available.
  # These primitives are documented in
  # <https://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Atomic-Builtins.html>
  # without platform restrictions. But they are not actually available
  # everywhere:
  #   * On some platforms, __sync_bool_compare_and_swap does not expand
  #     to standalone inline code, but to a call to a function
  #     '__sync_bool_compare_and_swap_4' (assuming a 32-bit value).
  #     This is the case on
  #       - arm,                                    for all gcc versions
  #       - hppa, hppa64,                           for all gcc versions
  #       - i386 (without '-march=i486'),           for all gcc versions
  #       - sparc (32-bit, for certain CPU models), for all gcc versions
  #       - m68k,                                   for gcc < 4.7
  #       - mips,                                   for gcc < 4.3
  #     This can be seen by compiling this piece of code
  #     ----------------------------------------------------------------
  #     int cmpxchg (int* value, int comp_val, int new_val)
  #     {
  #       return __sync_val_compare_and_swap (value, comp_val, new_val);
  #     }
  #     ----------------------------------------------------------------
  #     with option -S, using a (native or cross-) compiler.
  #   * The function __sync_bool_compare_and_swap_4 is meant to be included
  #     in libgcc. And indeed, libgcc contains the source code for this
  #     function on
  #       - arm,          for gcc versions >= 4.7, but only for Linux
  #                       and (for gcc >= 5) FreeBSD,
  #       - hppa, hppa64, for gcc versions >= 4.7, but only for Linux
  #                       and (for gcc >= 13) NetBSD, OpenBSD, hppa64 HP-UX
  #       - i386,         never at all
  #       - sparc,        never at all
  #       - m68k,         for gcc versions >= 4.7, but only for Linux
  #       - mips,         never at all
  #   * The NetBSD C library provides this function on
  #       - arm, arm64,
  #       - i386,
  #       - sparc,
  #       - m68k,
  #       - riscv64.
  #     Other C libraries (e.g. glibc, musl libc) do not provide this function.
  # So, the use of these primitives results in a link error on:
  #   - arm, with gcc versions >= 4.1, < 4.7 on all systems except NetBSD,
  #          with gcc versions >= 4.7, < 5 on FreeBSD, OpenBSD, Android,
  #          with gcc versions >= 5 on OpenBSD, Android,
  #   - hppa, hppa64, with gcc versions >= 4.1, < 4.7 on all systems,
  #                   with gcc versions >= 4.7, < 13 on NetBSD, OpenBSD,
  #   - i386 (without '-march=i486'), with gcc versions >= 4.1
  #                                   on all systems except NetBSD,
  #   - sparc (32-bit, for certain CPU models), with gcc versions >= 4.1
  #                                             on all systems except NetBSD,
  #   - m68k, with gcc versions >= 4.1, < 4.7 on all systems except NetBSD,
  #   - mips, with gcc versions >= 4.1, < 4.3 on all systems.
  # Additionally, link errors can occur if - such as on glibc systems - the libgcc
  # functions are distributed through glibc, but the glibc version is older than
  # the gcc version.
  AC_DEFUN([gl_ATOMIC_COMPARE_AND_SWAP],
  [
    AC_CACHE_CHECK([for __sync_bool_compare_and_swap],
      [gl_cv_builtin_sync_bool_compare_and_swap],
      [AC_LINK_IFELSE(
         [AC_LANG_PROGRAM(
            [[int cmpxchg (int* value, int comp_val, int new_val)
              {
                return __sync_val_compare_and_swap (value, comp_val, new_val);
              }
            ]],
            [[]])
         ],
         [gl_cv_builtin_sync_bool_compare_and_swap=yes],
         [gl_cv_builtin_sync_bool_compare_and_swap=no])
      ])
    if test $gl_cv_builtin_sync_bool_compare_and_swap = yes; then
      AC_DEFINE([HAVE_ATOMIC_COMPARE_AND_SWAP_GCC41], [1],
        [Define to 1 if the GCC 4.1 primitives for atomic compare-and-swap can be used.])
    fi
  ])
  

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