| /* Copyright (C) 2012-2020 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 && defined(atomic_compare_exchange_n) |
| bool |
| SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, |
| int smodel, int fmodel UNUSED) |
| { |
| if (maybe_specialcase_relaxed(smodel)) |
| return atomic_compare_exchange_n (mptr, eptr, newval, false, |
| __ATOMIC_RELAXED, __ATOMIC_RELAXED); |
| else if (maybe_specialcase_acqrel(smodel)) |
| return atomic_compare_exchange_n (mptr, eptr, newval, false, |
| __ATOMIC_ACQ_REL, __ATOMIC_RELAXED); |
| else |
| return atomic_compare_exchange_n (mptr, eptr, newval, false, |
| __ATOMIC_SEQ_CST, __ATOMIC_RELAXED); |
| } |
| |
| #define DONE 1 |
| #endif /* HAVE_ATOMIC_CAS */ |
| |
| |
| /* If this type is not larger than word-sized, fall back to a word-sized |
| compare-and-swap loop, possibly assisted by the OS. */ |
| #if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w) |
| bool |
| SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, |
| int smodel, int fmodel) |
| { |
| UWORD mask, shift, weval, 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; |
| } |
| |
| weval = (UWORD)*eptr << shift; |
| wnewval = (UWORD)newval << shift; |
| woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED); |
| do |
| { |
| if ((woldval & mask) != weval) |
| goto failure; |
| t = (woldval & ~mask) | wnewval; |
| } |
| while (!atomic_compare_exchange_w (wptr, &woldval, t, true, |
| __ATOMIC_RELAXED, __ATOMIC_RELAXED)); |
| post_barrier (smodel); |
| return true; |
| |
| failure: |
| *eptr = woldval >> shift; |
| post_barrier (fmodel); |
| return false; |
| } |
| |
| #define DONE 1 |
| #endif /* HAVE_ATOMIC_CAS && N <= WORDSIZE */ |
| |
| |
| /* Otherwise, fall back to some sort of protection mechanism. */ |
| #if !DONE |
| bool |
| SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, |
| int smodel, int fmodel UNUSED) |
| { |
| UTYPE oldval; |
| UWORD magic; |
| bool ret; |
| |
| pre_seq_barrier (smodel); |
| magic = protect_start (mptr); |
| |
| oldval = *mptr; |
| ret = (oldval == *eptr); |
| if (ret) |
| *mptr = newval; |
| else |
| *eptr = oldval; |
| |
| protect_end (mptr, magic); |
| post_seq_barrier (smodel); |
| |
| return ret; |
| } |
| #endif |
| |
| EXPORT_ALIAS (SIZE(compare_exchange)); |