arch/xtensa/include/asm/byteorder.h

/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * Based on Linux/Xtensa kernel version
 *
 * Copyright (C) 2001 - 2007 Tensilica Inc.
 */

#ifndef _XTENSA_BYTEORDER_H
#define _XTENSA_BYTEORDER_H

#include <asm/types.h>

static inline __attribute__((const)) __u32 ___arch__swab32(__u32 x)
{
	__u32 res;

	/* instruction sequence from Xtensa ISA release 2/2000 */
	__asm__("ssai     8\n\t"
		"srli     %0, %1, 16\n\t"
		"src      %0, %0, %1\n\t"
		"src      %0, %0, %0\n\t"
		"src      %0, %1, %0\n"
		: "=&a" (res)
		: "a" (x)
		);
	return res;
}

static inline __attribute__((const)) __u16 ___arch__swab16(__u16 x)
{
	/*
	 * Given that 'short' values are signed (i.e., can be negative),
	 * we cannot assume that the upper 16-bits of the register are
	 * zero.  We are careful to mask values after shifting.
	 */

	/*
	 * There exists an anomaly between xt-gcc and xt-xcc.  xt-gcc
	 * inserts an extui instruction after putting this function inline
	 * to ensure that it uses only the least-significant 16 bits of
	 * the result.  xt-xcc doesn't use an extui, but assumes the
	 * __asm__ macro follows convention that the upper 16 bits of an
	 * 'unsigned short' result are still zero.  This macro doesn't
	 * follow convention; indeed, it leaves garbage in the upport 16
	 * bits of the register.
	 *
	 * Declaring the temporary variables 'res' and 'tmp' to be 32-bit
	 * types while the return type of the function is a 16-bit type
	 * forces both compilers to insert exactly one extui instruction
	 * (or equivalent) to mask off the upper 16 bits.
	 */

	__u32 res;
	__u32 tmp;

	__asm__("extui    %1, %2, 8, 8\n\t"
		"slli     %0, %2, 8\n\t"
		"or       %0, %0, %1\n"
		: "=&a" (res), "=&a" (tmp)
		: "a" (x)
		);

	return res;
}

#define __arch__swab32(x) ___arch__swab32(x)
#define __arch__swab16(x) ___arch__swab16(x)

#if !defined(__STRICT_ANSI__) || defined(__KERNEL__)
#  define __BYTEORDER_HAS_U64__
#  define __SWAB_64_THRU_32__
#endif

#ifdef __XTENSA_EL__
# include <linux/byteorder/little_endian.h>
#elif defined(__XTENSA_EB__)
# include <linux/byteorder/big_endian.h>
#else
# error processor byte order undefined!
#endif

#endif /* _XTENSA_BYTEORDER_H */