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Add shortcuts to SwapEndian_16() and SwapEndian_32() internal functions to improve optimization if called with constant inputs.

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This commit is contained in:
Dean Camera 2011-08-16 05:00:45 +00:00
parent ef4cff29c3
commit 3478178127
5 changed files with 53 additions and 25 deletions
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10
LUFA/Common/CompilerSpecific.h
View file

@ -70,26 +70,26 @@
*
* \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))
#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");
#define GCC_MEMORY_BARRIER() __asm__ __volatile__("" ::: "memory");
/** Evaluates to boolean true 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 true if the given value is known to be a compile time constant.
* \return Boolean true if the given value is known to be a compile time constant, false otherwise.
*/
#define GCC_IS_COMPILE_CONST(x) __builtin_constant_p(x)
#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
#define GCC_IS_COMPILE_CONST(x) 0
#endif
#endif

6
LUFA/Common/Endianness.h
View file

@ -394,6 +394,9 @@
static inline uint16_t SwapEndian_16(const uint16_t Word) ATTR_WARN_UNUSED_RESULT ATTR_CONST;
static inline uint16_t SwapEndian_16(const uint16_t Word)
{
if (GCC_IS_COMPILE_CONST(Word))
return SWAPENDIAN_16(Word);
uint8_t Temp;
union
@ -420,6 +423,9 @@
static inline uint32_t SwapEndian_32(const uint32_t DWord) ATTR_WARN_UNUSED_RESULT ATTR_CONST;
static inline uint32_t SwapEndian_32(const uint32_t DWord)
{
if (GCC_IS_COMPILE_CONST(DWord))
return SWAPENDIAN_32(DWord);
uint8_t Temp;
union