github.com/grailbio/base@v0.0.11/compress/libdeflate/compiler_gcc.h

#ifndef GO_SRC_GITHUB_COM_GRAILBIO_BASE_COMPRESS_LIBDEFLATE_COMPILER_GCC_H_
#define GO_SRC_GITHUB_COM_GRAILBIO_BASE_COMPRESS_LIBDEFLATE_COMPILER_GCC_H_
/*
 * compiler_gcc.h - definitions for the GNU C Compiler.  This also handles clang
 * and the Intel C Compiler (icc).
 *
 * TODO: icc is not well tested, so some things are currently disabled even
 * though they maybe can be enabled on some icc versions.
 */

#if !defined(__clang__) && !defined(__INTEL_COMPILER)
#  define GCC_PREREQ(major, minor)		\
	(__GNUC__ > (major) ||			\
	 (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor)))
#else
#  define GCC_PREREQ(major, minor)	0
#endif

/* Note: only check the clang version when absolutely necessary!
 * "Vendors" such as Apple can use different version numbers. */
#ifdef __clang__
#  ifdef __apple_build_version__
#    define CLANG_PREREQ(major, minor, apple_version)	\
	(__apple_build_version__ >= (apple_version))
#  else
#    define CLANG_PREREQ(major, minor, apple_version)	\
	(__clang_major__ > (major) ||			\
	 (__clang_major__ == (major) && __clang_minor__ >= (minor)))
#  endif
#else
#  define CLANG_PREREQ(major, minor, apple_version)	0
#endif

#ifndef __has_attribute
#  define __has_attribute(attribute)	0
#endif
#ifndef __has_feature
#  define __has_feature(feature)	0
#endif
#ifndef __has_builtin
#  define __has_builtin(builtin)	0
#endif

#ifdef _WIN32
#  define LIBEXPORT __declspec(dllexport)
#else
#  define LIBEXPORT __attribute__((visibility("default")))
#endif

#define inline			inline
#define forceinline		inline __attribute__((always_inline))
#define restrict		__restrict__
#define likely(expr)		__builtin_expect(!!(expr), 1)
#define unlikely(expr)		__builtin_expect(!!(expr), 0)
#define prefetchr(addr)		__builtin_prefetch((addr), 0)
#define prefetchw(addr)		__builtin_prefetch((addr), 1)
#define _aligned_attribute(n)	__attribute__((aligned(n)))

#define COMPILER_SUPPORTS_TARGET_FUNCTION_ATTRIBUTE	\
	(GCC_PREREQ(4, 4) || __has_attribute(target))

#if COMPILER_SUPPORTS_TARGET_FUNCTION_ATTRIBUTE

#  if defined(__i386__) || defined(__x86_64__)

#    define COMPILER_SUPPORTS_PCLMUL_TARGET	\
	(GCC_PREREQ(4, 4) || __has_builtin(__builtin_ia32_pclmulqdq128))

#    define COMPILER_SUPPORTS_AVX_TARGET	\
	(GCC_PREREQ(4, 6) || __has_builtin(__builtin_ia32_maxps256))

#    define COMPILER_SUPPORTS_BMI2_TARGET	\
	(GCC_PREREQ(4, 7) || __has_builtin(__builtin_ia32_pdep_di))

#    define COMPILER_SUPPORTS_AVX2_TARGET	\
	(GCC_PREREQ(4, 7) || __has_builtin(__builtin_ia32_pmaddwd256))

	/*
	 * Prior to gcc 4.9 (r200349) and clang 3.8 (r239883), x86 intrinsics
	 * not available in the main target could not be used in 'target'
	 * attribute functions.  Unfortunately clang has no feature test macro
	 * for this so we have to check its version.
	 */
#    if GCC_PREREQ(4, 9) || CLANG_PREREQ(3, 8, 7030000)
#      define COMPILER_SUPPORTS_SSE2_TARGET_INTRINSICS	1
#      define COMPILER_SUPPORTS_PCLMUL_TARGET_INTRINSICS	\
		COMPILER_SUPPORTS_PCLMUL_TARGET
#      define COMPILER_SUPPORTS_AVX2_TARGET_INTRINSICS	\
		COMPILER_SUPPORTS_AVX2_TARGET
#    endif
#  elif defined(__arm__) || defined(__aarch64__)
	/*
	 * Prior to gcc 6.1 (r230411 for arm, r226563 for aarch64), NEON
	 * and crypto intrinsics not available in the main target could not be
	 * used in 'target' attribute functions.
	 *
	 * clang as of 5.0.1 still doesn't allow it.  But, it does seem to allow
	 * the pmull intrinsics if only __ARM_NEON is enabled.
	 */
#    define COMPILER_SUPPORTS_NEON_TARGET_INTRINSICS	GCC_PREREQ(6, 1)
#    ifdef __ARM_NEON
#      define COMPILER_SUPPORTS_PMULL_TARGET_INTRINSICS	\
		(GCC_PREREQ(6, 1) || __has_builtin(__builtin_neon_vmull_p64))
#    else
#      define COMPILER_SUPPORTS_PMULL_TARGET_INTRINSICS	\
		(GCC_PREREQ(6, 1))
#    endif
#  endif
#endif /* COMPILER_SUPPORTS_TARGET_FUNCTION_ATTRIBUTE */

/* Newer gcc supports __BYTE_ORDER__.  Older gcc doesn't. */
#ifdef __BYTE_ORDER__
#  define CPU_IS_LITTLE_ENDIAN() (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
#endif

#if GCC_PREREQ(4, 8) || __has_builtin(__builtin_bswap16)
#  define bswap16	__builtin_bswap16
#endif

#if GCC_PREREQ(4, 3) || __has_builtin(__builtin_bswap32)
#  define bswap32	__builtin_bswap32
#endif

#if GCC_PREREQ(4, 3) || __has_builtin(__builtin_bswap64)
#  define bswap64	__builtin_bswap64
#endif

#if defined(__x86_64__) || defined(__i386__) || defined(__ARM_FEATURE_UNALIGNED) || defined(__powerpc64__)
#  define UNALIGNED_ACCESS_IS_FAST 1
#endif

/* With gcc, we can access unaligned memory through 'packed' structures. */
#define DEFINE_UNALIGNED_TYPE(type)				\
								\
struct type##unaligned {					\
	type v;							\
} __attribute__((packed));					\
								\
static forceinline type						\
load_##type##_unaligned(const void *p)				\
{								\
	return ((const struct type##unaligned *)p)->v;		\
}								\
								\
static forceinline void						\
store_##type##_unaligned(type v, void *p)			\
{								\
	((struct type##unaligned *)p)->v = v;			\
}

#define bsr32(n)	(31 - __builtin_clz(n))
#define bsr64(n)	(63 - __builtin_clzll(n))
#define bsf32(n)	__builtin_ctz(n)
#define bsf64(n)	__builtin_ctzll(n)

#endif  // GO_SRC_GITHUB_COM_GRAILBIO_BASE_COMPRESS_LIBDEFLATE_COMPILER_GCC_H_