///////////////////////////////////////////////////////////////////////////////
//
/// \file       crc_common.h
/// \brief      Some functions and macros for CRC32 and CRC64
//
//  Authors:    Lasse Collin
//              Ilya Kurdyukov
//              Hans Jansen
//              Jia Tan
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#ifndef LZMA_CRC_COMMON_H
#define LZMA_CRC_COMMON_H

#include "common.h"


#ifdef WORDS_BIGENDIAN
#	define A(x) ((x) >> 24)
#	define B(x) (((x) >> 16) & 0xFF)
#	define C(x) (((x) >> 8) & 0xFF)
#	define D(x) ((x) & 0xFF)

#	define S8(x) ((x) << 8)
#	define S32(x) ((x) << 32)

#else
#	define A(x) ((x) & 0xFF)
#	define B(x) (((x) >> 8) & 0xFF)
#	define C(x) (((x) >> 16) & 0xFF)
#	define D(x) ((x) >> 24)

#	define S8(x) ((x) >> 8)
#	define S32(x) ((x) >> 32)
#endif


// The inline keyword is only a suggestion to the compiler to substitute the
// body of the function into the places where it is called. If a function
// is large and called multiple times then compiler may choose to ignore the
// inline suggestion at a sometimes high performance cost.
//
// MSVC's __forceinline is a keyword that should be used in place of inline.
// If both __forceinline and inline are used, MSVC will issue a warning.
// Since MSVC's keyword is a replacement keyword, the lzma_always_inline
// macro must also contain the inline keyword when its not used in MSVC.
#ifdef _MSC_VER
#	define crc_always_inline __forceinline
#else
#	define crc_always_inline __attribute__((__always_inline__)) inline
#endif

#undef CRC_GENERIC
#undef CRC_CLMUL
#undef CRC_USE_IFUNC
#undef CRC_USE_GENERIC_FOR_SMALL_INPUTS

// If CLMUL cannot be used then only the generic slice-by-four is built.
#if !defined(HAVE_USABLE_CLMUL)
#	define CRC_GENERIC 1

// If CLMUL is allowed unconditionally in the compiler options then the
// generic version can be omitted. Note that this doesn't work with MSVC
// as I don't know how to detect the features here.
//
// NOTE: Keep this this in sync with crc32_table.c.
#elif (defined(__SSSE3__) && defined(__SSE4_1__) && defined(__PCLMUL__)) \
		|| (defined(__e2k__) && __iset__ >= 6)
#	define CRC_CLMUL 1

// Otherwise build both and detect at runtime which version to use.
#else
#	define CRC_GENERIC 1
#	define CRC_CLMUL 1

#	ifdef HAVE_FUNC_ATTRIBUTE_IFUNC
#		define CRC_USE_IFUNC 1
#	endif

/*
	// The generic code is much faster with 1-8-byte inputs and has
	// similar performance up to 16 bytes  at least in microbenchmarks
	// (it depends on input buffer alignment too). If both versions are
	// built, this #define will use the generic version for inputs up to
	// 16 bytes and CLMUL for bigger inputs. It saves a little in code
	// size since the special cases for 0-16-byte inputs will be omitted
	// from the CLMUL code.
#	ifndef CRC_USE_IFUNC
#		define CRC_USE_GENERIC_FOR_SMALL_INPUTS 1
#	endif
*/

#	if defined(_MSC_VER)
#		include <intrin.h>
#	elif defined(HAVE_CPUID_H)
#		include <cpuid.h>
#	endif

// is_clmul_supported() must be inlined in this header file because the
// ifunc resolver function may not support calling a function in another
// translation unit. Depending on compiler-toolchain and flags, a call to
// a function defined in another translation unit could result in a
// reference to the PLT, which is unsafe to do in an ifunc resolver. The
// ifunc resolver runs very early when loading a shared library, so the PLT
// entries may not be setup at that time. Inlining this function duplicates
// the function body in crc32_resolve() and crc64_resolve(), but this is
// acceptable because the function results in very few instructions.
static inline bool
is_clmul_supported(void)
{
	int success = 1;
	uint32_t r[4]; // eax, ebx, ecx, edx

#if defined(_MSC_VER)
	// This needs <intrin.h> with MSVC. ICC has it as a built-in
	// on all platforms.
	__cpuid(r, 1);
#elif defined(HAVE_CPUID_H)
	// Compared to just using __asm__ to run CPUID, this also checks
	// that CPUID is supported and saves and restores ebx as that is
	// needed with GCC < 5 with position-independent code (PIC).
	success = __get_cpuid(1, &r[0], &r[1], &r[2], &r[3]);
#else
	// Just a fallback that shouldn't be needed.
	__asm__("cpuid\n\t"
			: "=a"(r[0]), "=b"(r[1]), "=c"(r[2]), "=d"(r[3])
			: "a"(1), "c"(0));
#endif

	// Returns true if these are supported:
	// CLMUL (bit 1 in ecx)
	// SSSE3 (bit 9 in ecx)
	// SSE4.1 (bit 19 in ecx)
	const uint32_t ecx_mask = (1 << 1) | (1 << 9) | (1 << 19);
	return success && (r[2] & ecx_mask) == ecx_mask;

	// Alternative methods that weren't used:
	//   - ICC's _may_i_use_cpu_feature: the other methods should work too.
	//   - GCC >= 6 / Clang / ICX __builtin_cpu_supports("pclmul")
	//
	// CPUID decding is needed with MSVC anyway and older GCC. This keeps
	// the feature checks in the build system simpler too. The nice thing
	// about __builtin_cpu_supports would be that it generates very short
	// code as is it only reads a variable set at startup but a few bytes
	// doesn't matter here.
}

#endif

/// CRC32 implemented with the x86 CLMUL instruction.
extern uint32_t lzma_crc32_clmul(const uint8_t *buf, size_t size,
		uint32_t crc);

/// CRC64 implemented with the x86 CLMUL instruction.
extern uint64_t lzma_crc64_clmul(const uint8_t *buf, size_t size,
		uint64_t crc);

#endif