scummvm/common/endian.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.

 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * $URL$
 * $Id$
 *
 */

#ifndef COMMON_ENDIAN_H
#define COMMON_ENDIAN_H

#include "common/scummsys.h"

/**
 *  \file endian.h
 *  Endian conversion and byteswap conversion functions or macros
 *
 *  SWAP_BYTES_??(a)      - inverse byte order
 *  SWAP_CONSTANT_??(a)   - inverse byte order, implemented as macro.
 *                              Use with compiletime-constants only, the result will be a compiletime-constant aswell.
 *                              Unlike most other functions these can be used for eg. switch-case labels
 *
 *  READ_UINT??(a)        - read native value from pointer a
 *  READ_??_UINT??(a)     - read LE/BE value from pointer a and convert it to native
 *  WRITE_??_UINT??(a, v) - write native value v to pointer a with LE/BE encoding
 *  TO_??_??(a)           - convert native value v to LE/BE
 *  FROM_??_??(a)         - convert LE/BE value v to native
 *  CONSTANT_??_??(a)     - convert LE/BE value v to native, implemented as macro.
 *                              Use with compiletime-constants only, the result will be a compiletime-constant aswell.
 *                              Unlike most other functions these can be used for eg. switch-case labels
 */

// Sanity check
#if !defined(SCUMM_LITTLE_ENDIAN) && !defined(SCUMM_BIG_ENDIAN)
#	error No endianness defined
#endif

#define SWAP_CONSTANT_32(a) \
	((uint32)((((a) >> 24) & 0x00FF) | \
	          (((a) >>  8) & 0xFF00) | \
	          (((a) & 0xFF00) <<  8) | \
	          (((a) & 0x00FF) << 24) ))

#define SWAP_CONSTANT_16(a) \
	((uint16)((((a) >>  8) & 0x00FF) | \
	          (((a) <<  8) & 0xFF00) ))

/**
 * Swap the bytes in a 32 bit word in order to convert LE encoded data to BE
 * and vice versa.
 */

// machine/compiler-specific variants come first, fallback last

// Test for GCC and if the target has the MIPS rel.2 instructions (we know the psp does)
#if defined(__GNUC__) && (defined(__psp__) || defined(_MIPS_ARCH_MIPS32R2) || defined(_MIPS_ARCH_MIPS64R2))

	FORCEINLINE uint32 SWAP_BYTES_32(const uint32 a) {
		if (__builtin_constant_p(a)) {
			return SWAP_CONSTANT_32(a);
		} else {
			uint32 result;
#	if defined(__psp__)
			// use special allegrex instruction
			__asm__ ("wsbw %0,%1" : "=r" (result) : "r" (a));
#	else
			__asm__ ("wsbh %0,%1\n"
			         "rotr %0,%0,16" : "=r" (result) : "r" (a));
#	endif
			return result;
		}
	}

// Test for GCC >= 4.3.0 as this version added the bswap builtin
#elif defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))

	FORCEINLINE uint32 SWAP_BYTES_32(uint32 a) {
		return __builtin_bswap32(a);
	}

// test for MSVC 7 or newer
#elif defined(_MSC_VER) && _MSC_VER >= 1300

	FORCEINLINE uint32 SWAP_BYTES_32(uint32 a) {
		return _byteswap_ulong(a);
	}

// generic fallback
#else

	inline uint32 SWAP_BYTES_32(uint32 a) {
		const uint16 low = (uint16)a, high = (uint16)(a >> 16);
		return ((uint32)(uint16)((low >> 8) | (low << 8)) << 16)
			   | (uint16)((high >> 8) | (high << 8));
	}
#endif

/**
 * Swap the bytes in a 16 bit word in order to convert LE encoded data to BE
 * and vice versa.
 */

// compilerspecific variants come first, fallback last

// Test for GCC and if the target has the MIPS rel.2 instructions (we know the psp does)
#if defined(__GNUC__) && (defined(__psp__) || defined(_MIPS_ARCH_MIPS32R2) || defined(_MIPS_ARCH_MIPS64R2))

	FORCEINLINE uint16 SWAP_BYTES_16(const uint16 a) {
		if (__builtin_constant_p(a)) {
			return SWAP_CONSTANT_16(a);
		} else {
			uint16 result;
			__asm__ ("wsbh %0,%1" : "=r" (result) : "r" (a));
			return result;
		}
	}
#else

	inline uint16 SWAP_BYTES_16(const uint16 a) {
		return (a >> 8) | (a << 8);
	}
#endif


/**
 * A wrapper macro used around four character constants, like 'DATA', to
 * ensure portability. Typical usage: MKTAG('D','A','T','A').
 *
 * Why is this necessary? The C/C++ standard does not define the endianess to
 * be used for character constants. Hence if one uses multi-byte character
 * constants, a potential portability problem opens up.
 */
#define MKTAG(a0,a1,a2,a3) ((uint32)((a3) | ((a2) << 8) | ((a1) << 16) | ((a0) << 24)))

// Functions for reading/writing native Integers,
// this transparently handles the need for alignment

#if !defined(SCUMM_NEED_ALIGNMENT)

	FORCEINLINE uint16 READ_UINT16(const void *ptr) {
		return *(const uint16 *)(ptr);
	}

	FORCEINLINE uint32 READ_UINT32(const void *ptr) {
		return *(const uint32 *)(ptr);
	}

	FORCEINLINE void WRITE_UINT16(void *ptr, uint16 value) {
		*(uint16 *)(ptr) = value;
	}

	FORCEINLINE void WRITE_UINT32(void *ptr, uint32 value) {
		*(uint32 *)(ptr) = value;
	}

// test for GCC >= 4.0. these implementations will automatically use CPU-specific
// instructions for unaligned data when they are available (eg. MIPS)
#elif defined(__GNUC__) && (__GNUC__ >= 4)

	FORCEINLINE uint16 READ_UINT16(const void *ptr) {
		struct Unaligned16 { uint16 val; } __attribute__ ((__packed__, __may_alias__));
		return ((const Unaligned16 *)ptr)->val;
	}

	FORCEINLINE uint32 READ_UINT32(const void *ptr) {
		struct Unaligned32 { uint32 val; } __attribute__ ((__packed__, __may_alias__));
		return ((const Unaligned32 *)ptr)->val;
	}

	FORCEINLINE void WRITE_UINT16(void *ptr, uint16 value) {
		struct Unaligned16 { uint16 val; } __attribute__ ((__packed__, __may_alias__));
		((Unaligned16 *)ptr)->val = value;
	}

	FORCEINLINE void WRITE_UINT32(void *ptr, uint32 value) {
		struct Unaligned32 { uint32 val; } __attribute__ ((__packed__, __may_alias__));
		((Unaligned32 *)ptr)->val = value;
	}

// use software fallback by loading each byte explicitely
#else

#	if defined(SCUMM_LITTLE_ENDIAN)

		inline uint16 READ_UINT16(const void *ptr) {
			const uint8 *b = (const uint8 *)ptr;
			return (b[1] << 8) | b[0];
		}
		inline uint32 READ_UINT32(const void *ptr) {
			const uint8 *b = (const uint8 *)ptr;
			return (b[3] << 24) | (b[2] << 16) | (b[1] << 8) | (b[0]);
		}
		inline void WRITE_UINT16(void *ptr, uint16 value) {
			uint8 *b = (uint8 *)ptr;
			b[0] = (uint8)(value >> 0);
			b[1] = (uint8)(value >> 8);
		}
		inline void WRITE_UINT32(void *ptr, uint32 value) {
			uint8 *b = (uint8 *)ptr;
			b[0] = (uint8)(value >>  0);
			b[1] = (uint8)(value >>  8);
			b[2] = (uint8)(value >> 16);
			b[3] = (uint8)(value >> 24);
		}

#	elif defined(SCUMM_BIG_ENDIAN)

		inline uint16 READ_UINT16(const void *ptr) {
			const uint8 *b = (const uint8 *)ptr;
			return (b[0] << 8) | b[1];
		}
		inline uint32 READ_UINT32(const void *ptr) {
			const uint8 *b = (const uint8 *)ptr;
			return (b[0] << 24) | (b[1] << 16) | (b[2] << 8) | (b[3]);
		}
		inline void WRITE_UINT16(void *ptr, uint16 value) {
			uint8 *b = (uint8 *)ptr;
			b[0] = (uint8)(value >> 8);
			b[1] = (uint8)(value >> 0);
		}
		inline void WRITE_UINT32(void *ptr, uint32 value) {
			uint8 *b = (uint8 *)ptr;
			b[0] = (uint8)(value >> 24);
			b[1] = (uint8)(value >> 16);
			b[2] = (uint8)(value >>  8);
			b[3] = (uint8)(value >>  0);
		}

#	endif

#endif


//  Map Funtions for reading/writing BE/LE integers depending on native endianess
#if defined(SCUMM_LITTLE_ENDIAN)

	#define READ_LE_UINT16(a) READ_UINT16(a)
	#define READ_LE_UINT32(a) READ_UINT32(a)

	#define WRITE_LE_UINT16(a, v) WRITE_UINT16(a, v)
	#define WRITE_LE_UINT32(a, v) WRITE_UINT32(a, v)

	#define FROM_LE_32(a) ((uint32)(a))
	#define FROM_LE_16(a) ((uint16)(a))

	#define FROM_BE_32(a) SWAP_BYTES_32(a)
	#define FROM_BE_16(a) SWAP_BYTES_16(a)

	#define TO_LE_32(a) ((uint32)(a))
	#define TO_LE_16(a) ((uint16)(a))

	#define TO_BE_32(a) SWAP_BYTES_32(a)
	#define TO_BE_16(a) SWAP_BYTES_16(a)

	#define CONSTANT_LE_32(a) ((uint32)(a))
	#define CONSTANT_LE_16(a) ((uint16)(a))

	#define CONSTANT_BE_32(a) SWAP_CONSTANT_32(a)
	#define CONSTANT_BE_16(a) SWAP_CONSTANT_16(a)

// if the unaligned load and the byteswap take alot instructions its better to directly read and invert
#	if defined(SCUMM_NEED_ALIGNMENT) && !defined(__mips__)

		inline uint16 READ_BE_UINT16(const void *ptr) {
			const uint8 *b = (const uint8 *)ptr;
			return (b[0] << 8) | b[1];
		}
		inline uint32 READ_BE_UINT32(const void *ptr) {
			const uint8 *b = (const uint8 *)ptr;
			return (b[0] << 24) | (b[1] << 16) | (b[2] << 8) | (b[3]);
		}
		inline void WRITE_BE_UINT16(void *ptr, uint16 value) {
			uint8 *b = (uint8 *)ptr;
			b[0] = (uint8)(value >> 8);
			b[1] = (uint8)(value >> 0);
		}
		inline void WRITE_BE_UINT32(void *ptr, uint32 value) {
			uint8 *b = (uint8 *)ptr;
			b[0] = (uint8)(value >> 24);
			b[1] = (uint8)(value >> 16);
			b[2] = (uint8)(value >>  8);
			b[3] = (uint8)(value >>  0);
		}
#	else

		inline uint16 READ_BE_UINT16(const void *ptr) {
			return SWAP_BYTES_16(READ_UINT16(ptr));
		}
		inline uint32 READ_BE_UINT32(const void *ptr) {
			return SWAP_BYTES_32(READ_UINT32(ptr));
		}
		inline void WRITE_BE_UINT16(void *ptr, uint16 value) {
			WRITE_UINT16(ptr, SWAP_BYTES_16(value));
		}
		inline void WRITE_BE_UINT32(void *ptr, uint32 value) {
			WRITE_UINT32(ptr, SWAP_BYTES_32(value));
		}

#	endif	// if defined(SCUMM_NEED_ALIGNMENT)

#elif defined(SCUMM_BIG_ENDIAN)

	#define READ_BE_UINT16(a) READ_UINT16(a)
	#define READ_BE_UINT32(a) READ_UINT32(a)

	#define WRITE_BE_UINT16(a, v) WRITE_UINT16(a, v)
	#define WRITE_BE_UINT32(a, v) WRITE_UINT32(a, v)

	#define FROM_LE_32(a) SWAP_BYTES_32(a)
	#define FROM_LE_16(a) SWAP_BYTES_16(a)

	#define FROM_BE_32(a) ((uint32)(a))
	#define FROM_BE_16(a) ((uint16)(a))

	#define TO_LE_32(a) SWAP_BYTES_32(a)
	#define TO_LE_16(a) SWAP_BYTES_16(a)

	#define TO_BE_32(a) ((uint32)(a))
	#define TO_BE_16(a) ((uint16)(a))

	#define CONSTANT_LE_32(a) SWAP_CONSTANT_32(a)
	#define CONSTANT_LE_16(a) SWAP_CONSTANT_16(a)

	#define CONSTANT_BE_32(a) ((uint32)(a))
	#define CONSTANT_BE_16(a) ((uint16)(a))

// if the unaligned load and the byteswap take alot instructions its better to directly read and invert
#	if defined(SCUMM_NEED_ALIGNMENT) && !defined(__mips__)

	inline uint16 READ_LE_UINT16(const void *ptr) {
		const uint8 *b = (const uint8 *)ptr;
		return (b[1] << 8) | b[0];
	}
	inline uint32 READ_LE_UINT32(const void *ptr) {
		const uint8 *b = (const uint8 *)ptr;
		return (b[3] << 24) | (b[2] << 16) | (b[1] << 8) | (b[0]);
	}
	inline void WRITE_LE_UINT16(void *ptr, uint16 value) {
		uint8 *b = (uint8 *)ptr;
		b[0] = (uint8)(value >> 0);
		b[1] = (uint8)(value >> 8);
	}
	inline void WRITE_LE_UINT32(void *ptr, uint32 value) {
		uint8 *b = (uint8 *)ptr;
		b[0] = (uint8)(value >>  0);
		b[1] = (uint8)(value >>  8);
		b[2] = (uint8)(value >> 16);
		b[3] = (uint8)(value >> 24);
	}
#	else

	inline uint16 READ_LE_UINT16(const void *ptr) {
		return SWAP_BYTES_16(READ_UINT16(ptr));
	}
	inline uint32 READ_LE_UINT32(const void *ptr) {
		return SWAP_BYTES_32(READ_UINT32(ptr));
	}
	inline void WRITE_LE_UINT16(void *ptr, uint16 value) {
		WRITE_UINT16(ptr, SWAP_BYTES_16(value));
	}
	inline void WRITE_LE_UINT32(void *ptr, uint32 value) {
		WRITE_UINT32(ptr, SWAP_BYTES_32(value));
	}

#	endif	// if defined(SCUMM_NEED_ALIGNMENT)

#endif	// if defined(SCUMM_LITTLE_ENDIAN)

inline uint32 READ_LE_UINT24(const void *ptr) {
	const uint8 *b = (const uint8 *)ptr;
	return (b[2] << 16) | (b[1] << 8) | (b[0]);
}

inline uint32 READ_BE_UINT24(const void *ptr) {
	const uint8 *b = (const uint8 *)ptr;
	return (b[0] << 16) | (b[1] << 8) | (b[2]);
}

#endif