Merge commit '60b30c036397cb5627fa374bb930794b225daa29' as 'lib/lufa'

[qmk_firmware.git] / lib / lufa / LUFA / Common / CompilerSpecific.h

diff --git a/lib/lufa/LUFA/Common/CompilerSpecific.h b/lib/lufa/LUFA/Common/CompilerSpecific.h
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+/*
+             LUFA Library
+     Copyright (C) Dean Camera, 2017.
+
+  dean [at] fourwalledcubicle [dot] com
+           www.lufa-lib.org
+*/
+
+/*
+  Copyright 2017  Dean Camera (dean [at] fourwalledcubicle [dot] com)
+
+  Permission to use, copy, modify, distribute, and sell this
+  software and its documentation for any purpose is hereby granted
+  without fee, provided that the above copyright notice appear in
+  all copies and that both that the copyright notice and this
+  permission notice and warranty disclaimer appear in supporting
+  documentation, and that the name of the author not be used in
+  advertising or publicity pertaining to distribution of the
+  software without specific, written prior permission.
+
+  The author disclaims all warranties with regard to this
+  software, including all implied warranties of merchantability
+  and fitness.  In no event shall the author be liable for any
+  special, indirect or consequential damages or any damages
+  whatsoever resulting from loss of use, data or profits, whether
+  in an action of contract, negligence or other tortious action,
+  arising out of or in connection with the use or performance of
+  this software.
+*/
+
+/** \file
+ *  \brief Compiler specific definitions for code optimization and correctness.
+ *
+ *  \copydetails Group_CompilerSpecific
+ *
+ *  \note Do not include this file directly, rather include the Common.h header file instead to gain this file's
+ *        functionality.
+ */
+
+/** \ingroup Group_Common
+ *  \defgroup Group_CompilerSpecific Compiler Specific Definitions
+ *  \brief Compiler specific definitions for code optimization and correctness.
+ *
+ *  Compiler specific definitions to expose certain compiler features which may increase the level of code optimization
+ *  for a specific compiler, or correct certain issues that may be present such as memory barriers for use in conjunction
+ *  with atomic variable access.
+ *
+ *  Where possible, on alternative compilers, these macros will either have no effect, or default to returning a sane value
+ *  so that they can be used in existing code without the need for extra compiler checks in the user application code.
+ *
+ *  @{
+ */
+
+#ifndef __LUFA_COMPILERSPEC_H__
+#define __LUFA_COMPILERSPEC_H__
+
+       /* Preprocessor Checks: */
+               #if !defined(__INCLUDE_FROM_COMMON_H)
+                       #error Do not include this file directly. Include LUFA/Common/Common.h instead to gain this functionality.
+               #endif
+
+       /* Public Interface - May be used in end-application: */
+               /* Macros: */
+                       #if defined(__GNUC__) || defined(__DOXYGEN__)
+                               /** Forces GCC to use pointer indirection (via the device's pointer register pairs) when accessing the given
+                                *  struct pointer. In some cases GCC will emit non-optimal assembly code when accessing a structure through
+                                *  a pointer, resulting in a larger binary. When this macro is used on a (non \c const) structure pointer before
+                                *  use, it will force GCC to use pointer indirection on the elements rather than direct store and load
+                                *  instructions.
+                                *
+                                *  \param[in, out] StructPtr  Pointer to a structure which is to be forced into indirect access mode.
+                                */
+                               #define GCC_FORCE_POINTER_ACCESS(StructPtr)   __asm__ __volatile__("" : "=b" (StructPtr) : "0" (StructPtr))
+
+                               /** Forces GCC to create a memory barrier, ensuring that memory accesses are not reordered past the barrier point.
+                                *  This can be used before ordering-critical operations, to ensure that the compiler does not re-order the resulting
+                                *  assembly output in an unexpected manner on sections of code that are ordering-specific.
+                                */
+                               #define GCC_MEMORY_BARRIER()                  __asm__ __volatile__("" ::: "memory");
+
+                               /** Determines if the specified value can be determined at compile-time to be a constant value when compiling under GCC.
+                                *
+                                *  \param[in] x  Value to check compile-time constantness of.
+                                *
+                                *  \return Boolean \c true if the given value is known to be a compile time constant, \c false otherwise.
+                                */
+                               #define GCC_IS_COMPILE_CONST(x)               __builtin_constant_p(x)
+                       #else
+                               #define GCC_FORCE_POINTER_ACCESS(StructPtr)
+                               #define GCC_MEMORY_BARRIER()
+                               #define GCC_IS_COMPILE_CONST(x)               0
+                       #endif
+
+#endif
+
+/** @} */
+