text: // -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
  // Copyright (c) 2003, Google Inc.
  // All rights reserved.
  //
  // Redistribution and use in source and binary forms, with or without
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  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  //     * Neither the name of Google Inc. nor the names of its
  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  // ---
  //
  // Author: Lei Zhang, Sasha Levitskiy
  //
  // This file is an internal atomic implementation, use base/atomicops.h instead.
  //
  // LinuxKernelCmpxchg and Barrier_AtomicIncrement are from Google Gears.
  
  #ifndef BASE_ATOMICOPS_INTERNALS_ARM_GENERIC_H_
  #define BASE_ATOMICOPS_INTERNALS_ARM_GENERIC_H_
  
  #include <stdio.h>
  #include <stdlib.h>
  #include "base/basictypes.h"
  
  typedef int32_t Atomic32;
  
  namespace base {
  namespace subtle {
  
  typedef int64_t Atomic64;
  
  // 0xffff0fc0 is the hard coded address of a function provided by
  // the kernel which implements an atomic compare-exchange. On older
  // ARM architecture revisions (pre-v6) this may be implemented using
  // a syscall. This address is stable, and in active use (hard coded)
  // by at least glibc-2.7 and the Android C library.
  // pLinuxKernelCmpxchg has both acquire and release barrier sematincs.
  typedef Atomic32 (*LinuxKernelCmpxchgFunc)(Atomic32 old_value,
                                             Atomic32 new_value,
                                             volatile Atomic32* ptr);
  LinuxKernelCmpxchgFunc pLinuxKernelCmpxchg ATTRIBUTE_WEAK =
      (LinuxKernelCmpxchgFunc) 0xffff0fc0;
  
  typedef void (*LinuxKernelMemoryBarrierFunc)(void);
  LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier ATTRIBUTE_WEAK =
      (LinuxKernelMemoryBarrierFunc) 0xffff0fa0;
  
  
  inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
                                           Atomic32 old_value,
                                           Atomic32 new_value) {
    Atomic32 prev_value = *ptr;
    do {
      if (!pLinuxKernelCmpxchg(old_value, new_value,
                               const_cast<Atomic32*>(ptr))) {
        return old_value;
      }
      prev_value = *ptr;
    } while (prev_value == old_value);
    return prev_value;
  }
  
  inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
                                           Atomic32 new_value) {
    Atomic32 old_value;
    do {
      old_value = *ptr;
    } while (pLinuxKernelCmpxchg(old_value, new_value,
                                 const_cast<Atomic32*>(ptr)));
    return old_value;
  }
  
  inline Atomic32 Acquire_AtomicExchange(volatile Atomic32* ptr,
                                         Atomic32 new_value) {
    // pLinuxKernelCmpxchg already has acquire and release barrier semantics.
    return NoBarrier_AtomicExchange(ptr, new_value);
  }
  
  inline Atomic32 Release_AtomicExchange(volatile Atomic32* ptr,
                                         Atomic32 new_value) {
    // pLinuxKernelCmpxchg already has acquire and release barrier semantics.
    return NoBarrier_AtomicExchange(ptr, new_value);
  }
  
  inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
                                          Atomic32 increment) {
    for (;;) {
      // Atomic exchange the old value with an incremented one.
      Atomic32 old_value = *ptr;
      Atomic32 new_value = old_value + increment;
      if (pLinuxKernelCmpxchg(old_value, new_value,
                              const_cast<Atomic32*>(ptr)) == 0) {
        // The exchange took place as expected.
        return new_value;
      }
      // Otherwise, *ptr changed mid-loop and we need to retry.
    }
  }
  
  inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
                                            Atomic32 increment) {
    return Barrier_AtomicIncrement(ptr, increment);
  }
  
  inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
                                         Atomic32 old_value,
                                         Atomic32 new_value) {
    return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
  }
  
  inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
                                         Atomic32 old_value,
                                         Atomic32 new_value) {
    return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
  }
  
  inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
    *ptr = value;
  }
  
  inline void MemoryBarrier() {
    pLinuxKernelMemoryBarrier();
  }
  
  inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
    *ptr = value;
    MemoryBarrier();
  }
  
  inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
    MemoryBarrier();
    *ptr = value;
  }
  
  inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
    return *ptr;
  }
  
  inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
    Atomic32 value = *ptr;
    MemoryBarrier();
    return value;
  }
  
  inline Atomic32 Release_Load(volatile const Atomic32* ptr) {
    MemoryBarrier();
    return *ptr;
  }
  
  
  // 64-bit versions are not implemented yet.
  
  inline void NotImplementedFatalError(const char *function_name) {
    fprintf(stderr, "64-bit %s() not implemented on this platform\n",
            function_name);
    abort();
  }
  
  inline Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr,
                                           Atomic64 old_value,
                                           Atomic64 new_value) {
    NotImplementedFatalError("NoBarrier_CompareAndSwap");
    return 0;
  }
  
  inline Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr,
                                           Atomic64 new_value) {
    NotImplementedFatalError("NoBarrier_AtomicExchange");
    return 0;
  }
  
  inline Atomic64 Acquire_AtomicExchange(volatile Atomic64* ptr,
                                         Atomic64 new_value) {
    // pLinuxKernelCmpxchg already has acquire and release barrier semantics.
    return NoBarrier_AtomicExchange(ptr, new_value);
  }
  
  inline Atomic64 Release_AtomicExchange(volatile Atomic64* ptr,
                                         Atomic64 new_value) {
    // pLinuxKernelCmpxchg already has acquire and release barrier semantics.
    return NoBarrier_AtomicExchange(ptr, new_value);
  }
  
  inline Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr,
                                            Atomic64 increment) {
    NotImplementedFatalError("NoBarrier_AtomicIncrement");
    return 0;
  }
  
  inline Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr,
                                          Atomic64 increment) {
    NotImplementedFatalError("Barrier_AtomicIncrement");
    return 0;
  }
  
  inline void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value) {
    NotImplementedFatalError("NoBarrier_Store");
  }
  
  inline void Acquire_Store(volatile Atomic64* ptr, Atomic64 value) {
    NotImplementedFatalError("Acquire_Store64");
  }
  
  inline void Release_Store(volatile Atomic64* ptr, Atomic64 value) {
    NotImplementedFatalError("Release_Store");
  }
  
  inline Atomic64 NoBarrier_Load(volatile const Atomic64* ptr) {
    NotImplementedFatalError("NoBarrier_Load");
    return 0;
  }
  
  inline Atomic64 Acquire_Load(volatile const Atomic64* ptr) {
    NotImplementedFatalError("Atomic64 Acquire_Load");
    return 0;
  }
  
  inline Atomic64 Release_Load(volatile const Atomic64* ptr) {
    NotImplementedFatalError("Atomic64 Release_Load");
    return 0;
  }
  
  inline Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
                                         Atomic64 old_value,
                                         Atomic64 new_value) {
    NotImplementedFatalError("Atomic64 Acquire_CompareAndSwap");
    return 0;
  }
  
  inline Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr,
                                         Atomic64 old_value,
                                         Atomic64 new_value) {
    NotImplementedFatalError("Atomic64 Release_CompareAndSwap");
    return 0;
  }
  
  }  // namespace base::subtle
  }  // namespace base
  
  #endif  // BASE_ATOMICOPS_INTERNALS_ARM_GENERIC_H_
  