/* Copyright (C) 2012-2022 Free Software Foundation, Inc. Contributed by Richard Henderson <rth@redhat.com>. This file is part of the GNU Atomic Library (libatomic). Libatomic is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. Under Section 7 of GPL version 3, you are granted additional permissions described in the GCC Runtime Library Exception, version 3.1, as published by the Free Software Foundation. You should have received a copy of the GNU General Public License and a copy of the GCC Runtime Library Exception along with this program; see the files COPYING3 and COPYING.RUNTIME respectively. If not, see <http://www.gnu.org/licenses/>. */ #include "libatomic_i.h" /* If we support the builtin, just use it. */ #if !DONE && SIZE(HAVE_ATOMIC_EXCHANGE) UTYPE SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel) { if (maybe_specialcase_relaxed(smodel)) return __atomic_exchange_n (mptr, newval, __ATOMIC_RELAXED); else if (maybe_specialcase_acqrel(smodel)) return __atomic_exchange_n (mptr, newval, __ATOMIC_ACQ_REL); else return __atomic_exchange_n (mptr, newval, __ATOMIC_SEQ_CST); } #define DONE 1 #endif /* HAVE_ATOMIC_EXCHANGE */ #if !DONE && defined(atomic_compare_exchange_n) UTYPE SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel) { UTYPE oldval; pre_barrier (smodel); oldval = *mptr; while (!atomic_compare_exchange_n (mptr, &oldval, newval, true, __ATOMIC_RELAXED, __ATOMIC_RELAXED)) continue; post_barrier (smodel); return oldval; } #define DONE 1 #endif /* atomic_compare_exchange_n */ /* If this type is smaller than word-sized, fall back to a word-sized compare-and-swap loop. */ #if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w) UTYPE SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel) { UWORD mask, shift, woldval, wnewval, t, *wptr; pre_barrier (smodel); if (N < WORDSIZE) { wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE); shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK); mask = SIZE(MASK) << shift; } else { wptr = (UWORD *)mptr; shift = 0; mask = -1; } wnewval = (UWORD)newval << shift; woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED); do { t = (woldval & ~mask) | wnewval; } while (!atomic_compare_exchange_w (wptr, &woldval, t, true, __ATOMIC_RELAXED, __ATOMIC_RELAXED)); post_barrier (smodel); return woldval >> shift; } #define DONE 1 #endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */ /* Otherwise, fall back to some sort of protection mechanism. */ #if !DONE UTYPE SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel UNUSED) { UTYPE oldval; UWORD magic; pre_seq_barrier (smodel); magic = protect_start (mptr); oldval = *mptr; *mptr = newval; protect_end (mptr, magic); post_seq_barrier (smodel); return oldval; } #endif EXPORT_ALIAS (SIZE(exchange));