libdeflate/lib/unaligned.h

/*
 * unaligned.h - inline functions for unaligned memory accesses
 */

#ifndef LIB_UNALIGNED_H
#define LIB_UNALIGNED_H

#include "lib_common.h"

/***** Unaligned loads and stores without endianness conversion *****/

/*
 * memcpy() is portable, and it usually gets optimized appropriately by modern
 * compilers.  I.e., each memcpy() of 1, 2, 4, or WORDBYTES bytes gets compiled
 * to a load or store instruction, not to an actual function call.
 *
 * We no longer use the "packed struct" approach, as that is nonstandard, has
 * unclear semantics, and doesn't receive enough testing
 * (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94994).
 *
 * arm32 with __ARM_FEATURE_UNALIGNED in gcc 5 and earlier is a known exception
 * where memcpy() generates inefficient code
 * (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67366).  However, we no longer
 * consider that one case important enough to maintain different code for.
 * If you run into it, please just use a newer version of gcc (or use clang).
 */

#define DEFINE_UNALIGNED_TYPE(type)				\
static forceinline type						\
load_##type##_unaligned(const void *p)				\
{								\
	type v;							\
	memcpy(&v, p, sizeof(v));				\
	return v;						\
}								\
								\
static forceinline void						\
store_##type##_unaligned(type v, void *p)			\
{								\
	memcpy(p, &v, sizeof(v));				\
}

DEFINE_UNALIGNED_TYPE(u16)
DEFINE_UNALIGNED_TYPE(u32)
DEFINE_UNALIGNED_TYPE(u64)
DEFINE_UNALIGNED_TYPE(machine_word_t)

#define load_word_unaligned	load_machine_word_t_unaligned
#define store_word_unaligned	store_machine_word_t_unaligned

/***** Unaligned loads with endianness conversion *****/

static forceinline u16
get_unaligned_le16(const u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST)
		return le16_bswap(load_u16_unaligned(p));
	else
		return ((u16)p[1] << 8) | p[0];
}

static forceinline u16
get_unaligned_be16(const u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST)
		return be16_bswap(load_u16_unaligned(p));
	else
		return ((u16)p[0] << 8) | p[1];
}

static forceinline u32
get_unaligned_le32(const u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST)
		return le32_bswap(load_u32_unaligned(p));
	else
		return ((u32)p[3] << 24) | ((u32)p[2] << 16) |
			((u32)p[1] << 8) | p[0];
}

static forceinline u32
get_unaligned_be32(const u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST)
		return be32_bswap(load_u32_unaligned(p));
	else
		return ((u32)p[0] << 24) | ((u32)p[1] << 16) |
			((u32)p[2] << 8) | p[3];
}

static forceinline u64
get_unaligned_le64(const u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST)
		return le64_bswap(load_u64_unaligned(p));
	else
		return ((u64)p[7] << 56) | ((u64)p[6] << 48) |
			((u64)p[5] << 40) | ((u64)p[4] << 32) |
			((u64)p[3] << 24) | ((u64)p[2] << 16) |
			((u64)p[1] << 8) | p[0];
}

static forceinline machine_word_t
get_unaligned_leword(const u8 *p)
{
	STATIC_ASSERT(WORDBITS == 32 || WORDBITS == 64);
	if (WORDBITS == 32)
		return get_unaligned_le32(p);
	else
		return get_unaligned_le64(p);
}

/***** Unaligned stores with endianness conversion *****/

static forceinline void
put_unaligned_le16(u16 v, u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST) {
		store_u16_unaligned(le16_bswap(v), p);
	} else {
		p[0] = (u8)(v >> 0);
		p[1] = (u8)(v >> 8);
	}
}

static forceinline void
put_unaligned_be16(u16 v, u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST) {
		store_u16_unaligned(be16_bswap(v), p);
	} else {
		p[0] = (u8)(v >> 8);
		p[1] = (u8)(v >> 0);
	}
}

static forceinline void
put_unaligned_le32(u32 v, u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST) {
		store_u32_unaligned(le32_bswap(v), p);
	} else {
		p[0] = (u8)(v >> 0);
		p[1] = (u8)(v >> 8);
		p[2] = (u8)(v >> 16);
		p[3] = (u8)(v >> 24);
	}
}

static forceinline void
put_unaligned_be32(u32 v, u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST) {
		store_u32_unaligned(be32_bswap(v), p);
	} else {
		p[0] = (u8)(v >> 24);
		p[1] = (u8)(v >> 16);
		p[2] = (u8)(v >> 8);
		p[3] = (u8)(v >> 0);
	}
}

static forceinline void
put_unaligned_le64(u64 v, u8 *p)
{
	if (UNALIGNED_ACCESS_IS_FAST) {
		store_u64_unaligned(le64_bswap(v), p);
	} else {
		p[0] = (u8)(v >> 0);
		p[1] = (u8)(v >> 8);
		p[2] = (u8)(v >> 16);
		p[3] = (u8)(v >> 24);
		p[4] = (u8)(v >> 32);
		p[5] = (u8)(v >> 40);
		p[6] = (u8)(v >> 48);
		p[7] = (u8)(v >> 56);
	}
}

static forceinline void
put_unaligned_leword(machine_word_t v, u8 *p)
{
	STATIC_ASSERT(WORDBITS == 32 || WORDBITS == 64);
	if (WORDBITS == 32)
		put_unaligned_le32(v, p);
	else
		put_unaligned_le64(v, p);
}

/***** 24-bit loads *****/

/*
 * Given a 32-bit value that was loaded with the platform's native endianness,
 * return a 32-bit value whose high-order 8 bits are 0 and whose low-order 24
 * bits contain the first 3 bytes, arranged in octets in a platform-dependent
 * order, at the memory location from which the input 32-bit value was loaded.
 */
static forceinline u32
loaded_u32_to_u24(u32 v)
{
	if (CPU_IS_LITTLE_ENDIAN())
		return v & 0xFFFFFF;
	else
		return v >> 8;
}

/*
 * Load the next 3 bytes from the memory location @p into the 24 low-order bits
 * of a 32-bit value.  The order in which the 3 bytes will be arranged as octets
 * in the 24 bits is platform-dependent.  At least LOAD_U24_REQUIRED_NBYTES
 * bytes must be available at @p; note that this may be more than 3.
 */
static forceinline u32
load_u24_unaligned(const u8 *p)
{
#if UNALIGNED_ACCESS_IS_FAST
#  define LOAD_U24_REQUIRED_NBYTES 4
	return loaded_u32_to_u24(load_u32_unaligned(p));
#else
#  define LOAD_U24_REQUIRED_NBYTES 3
	if (CPU_IS_LITTLE_ENDIAN())
		return ((u32)p[0] << 0) | ((u32)p[1] << 8) | ((u32)p[2] << 16);
	else
		return ((u32)p[2] << 0) | ((u32)p[1] << 8) | ((u32)p[0] << 16);
#endif
}

#endif /* LIB_UNALIGNED_H */