/*

Simple DirectMedia Layer

Copyright (C) 1997-2013 Sam Lantinga <slouken@libsdl.org>

This software is provided 'as-is', without any express or implied

warranty. In no event will the authors be held liable for any damages

arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,

including commercial applications, and to alter it and redistribute it

freely, subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not

claim that you wrote the original software. If you use this software

in a product, an acknowledgment in the product documentation would be

appreciated but is not required.

2. Altered source versions must be plainly marked as such, and must not be

misrepresented as being the original software.

3. This notice may not be removed or altered from any source distribution.

*/

#include "SDL_atomic.h"

#if defined(_MSC_VER) && (_MSC_VER >= 1500)

#include <intrin.h>

#define HAVE_MSC_ATOMICS 1

#endif

#if defined(__MACOSX__) /* !!! FIXME: should we favor gcc atomics? */

#include <libkern/OSAtomic.h>

#endif

/*

If any of the operations are not provided then we must emulate some

of them. That means we need a nice implementation of spin locks

that avoids the "one big lock" problem. We use a vector of spin

locks and pick which one to use based on the address of the operand

of the function.

To generate the index of the lock we first shift by 3 bits to get

rid on the zero bits that result from 32 and 64 bit allignment of

data. We then mask off all but 5 bits and use those 5 bits as an

index into the table.

Picking the lock this way insures that accesses to the same data at

the same time will go to the same lock. OTOH, accesses to different

data have only a 1/32 chance of hitting the same lock. That should

pretty much eliminate the chances of several atomic operations on

different data from waiting on the same "big lock". If it isn't

then the table of locks can be expanded to a new size so long as

the new size is a power of two.

Contributed by Bob Pendleton, bob@pendleton.com

*/

#if !defined(HAVE_MSC_ATOMICS) && !defined(HAVE_GCC_ATOMICS) && !defined(__MACOSX__)

#define EMULATE_CAS 1

#endif

#if EMULATE_CAS

static SDL_SpinLock locks[32];

static SDL_INLINE void

enterLock(void *a)

{

uintptr_t index = ((((uintptr_t)a) >> 3) & 0x1f);

SDL_AtomicLock(&locks[index]);

}

static SDL_INLINE void

leaveLock(void *a)

{

uintptr_t index = ((((uintptr_t)a) >> 3) & 0x1f);

SDL_AtomicUnlock(&locks[index]);

}

SDL_bool

SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval)

{

#ifdef HAVE_MSC_ATOMICS

return (_InterlockedCompareExchange((long*)&a->value, (long)newval, (long)oldval) == (long)oldval);

#elif defined(__MACOSX__) /* !!! FIXME: should we favor gcc atomics? */

return (SDL_bool) OSAtomicCompareAndSwap32Barrier(oldval, newval, &a->value);

#elif defined(HAVE_GCC_ATOMICS)

return (SDL_bool) __sync_bool_compare_and_swap(&a->value, oldval, newval);

#elif EMULATE_CAS

SDL_bool retval = SDL_FALSE;

enterLock(a);

if (a->value == oldval) {

a->value = newval;

retval = SDL_TRUE;

}

leaveLock(a);

return retval;

#else

#error Please define your platform.

#endif

}

SDL_AtomicCASPtr(void **a, void *oldval, void *newval)

{

#if defined(HAVE_MSC_ATOMICS) && (_M_IX86)

return (_InterlockedCompareExchange((long*)a, (long)newval, (long)oldval) == (long)oldval);

#elif defined(HAVE_MSC_ATOMICS) && (!_M_IX86)

return (_InterlockedCompareExchangePointer(a, newval, oldval) == oldval);

#elif defined(__MACOSX__) && defined(__LP64__) /* !!! FIXME: should we favor gcc atomics? */

return (SDL_bool) OSAtomicCompareAndSwap64Barrier((int64_t)oldval, (int64_t)newval, (int64_t*) a);

#elif defined(__MACOSX__) && !defined(__LP64__) /* !!! FIXME: should we favor gcc atomics? */

return (SDL_bool) OSAtomicCompareAndSwap32Barrier((int32_t)oldval, (int32_t)newval, (int32_t*) a);

#elif defined(HAVE_GCC_ATOMICS)

return __sync_bool_compare_and_swap(a, oldval, newval);

#elif EMULATE_CAS

SDL_bool retval = SDL_FALSE;

enterLock(a);

if (*a == oldval) {

*a = newval;

retval = SDL_TRUE;

}

leaveLock(a);

return retval;

#else

#error Please define your platform.

#endif

}

int

SDL_AtomicSet(SDL_atomic_t *a, int v)

{

#ifdef HAVE_MSC_ATOMICS

return _InterlockedExchange((long*)&a->value, v);

#elif defined(HAVE_GCC_ATOMICS)

return __sync_lock_test_and_set(&a->value, v);

#else

int value;

do {

value = a->value;

} while (!SDL_AtomicCAS(a, value, v));

return value;

#endif

}

void*

SDL_AtomicSetPtr(void **a, void *v)

{

#if defined(HAVE_MSC_ATOMICS) && (_M_IX86)

return (void *) _InterlockedExchange((long *)a, (long) v);

#elif defined(HAVE_MSC_ATOMICS) && (!_M_IX86)

return _InterlockedExchangePointer(a, v);

#elif defined(HAVE_GCC_ATOMICS)

return __sync_lock_test_and_set(a, v);

#else

void *value;

do {

value = *a;

} while (!SDL_AtomicCASPtr(a, value, v));

return value;

#endif

}

int

SDL_AtomicAdd(SDL_atomic_t *a, int v)

{

#ifdef HAVE_MSC_ATOMICS

return _InterlockedExchangeAdd((long*)&a->value, v);

#elif defined(HAVE_GCC_ATOMICS)

return __sync_fetch_and_add(&a->value, v);

#else

int value;

do {

value = a->value;

} while (!SDL_AtomicCAS(a, value, (value + v)));

return value;

#endif

}

int

SDL_AtomicGet(SDL_atomic_t *a)

{

int value;

do {

value = a->value;

} while (!SDL_AtomicCAS(a, value, value));

return value;

}

void *

SDL_AtomicGetPtr(void **a)

{

void *value;

do {

value = *a;

} while (!SDL_AtomicCASPtr(a, value, value));

return value;

}

__asm__(

" .align 2\n"

" .globl _SDL_MemoryBarrierRelease\n"

" .globl _SDL_MemoryBarrierAcquire\n"

"_SDL_MemoryBarrierRelease:\n"

"_SDL_MemoryBarrierAcquire:\n"

" mov r0, #0\n"

" mcr p15, 0, r0, c7, c10, 5\n"

" bx lr\n"

);

/* vi: set ts=4 sw=4 expandtab: */