[linux.git] / lib / packing.c

// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
/* Copyright 2016-2018 NXP
 * Copyright (c) 2018-2019, Vladimir Oltean <[email protected]>
 */
#include <linux/packing.h>
#include <linux/module.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/bitrev.h>

static int get_le_offset(int offset)
{
	int closest_multiple_of_4;

	closest_multiple_of_4 = (offset / 4) * 4;
	offset -= closest_multiple_of_4;
	return closest_multiple_of_4 + (3 - offset);
}

static int get_reverse_lsw32_offset(int offset, size_t len)
{
	int closest_multiple_of_4;
	int word_index;

	word_index = offset / 4;
	closest_multiple_of_4 = word_index * 4;
	offset -= closest_multiple_of_4;
	word_index = (len / 4) - word_index - 1;
	return word_index * 4 + offset;
}

static void adjust_for_msb_right_quirk(u64 *to_write, int *box_start_bit,
				       int *box_end_bit, u8 *box_mask)
{
	int box_bit_width = *box_start_bit - *box_end_bit + 1;
	int new_box_start_bit, new_box_end_bit;

	*to_write >>= *box_end_bit;
	*to_write = bitrev8(*to_write) >> (8 - box_bit_width);
	*to_write <<= *box_end_bit;

	new_box_end_bit   = box_bit_width - *box_start_bit - 1;
	new_box_start_bit = box_bit_width - *box_end_bit - 1;
	*box_mask = GENMASK_ULL(new_box_start_bit, new_box_end_bit);
	*box_start_bit = new_box_start_bit;
	*box_end_bit   = new_box_end_bit;
}

/**
 * packing - Convert numbers (currently u64) between a packed and an unpacked
 *	     format. Unpacked means laid out in memory in the CPU's native
 *	     understanding of integers, while packed means anything else that
 *	     requires translation.
 *
 * @pbuf: Pointer to a buffer holding the packed value.
 * @uval: Pointer to an u64 holding the unpacked value.
 * @startbit: The index (in logical notation, compensated for quirks) where
 *	      the packed value starts within pbuf. Must be larger than, or
 *	      equal to, endbit.
 * @endbit: The index (in logical notation, compensated for quirks) where
 *	    the packed value ends within pbuf. Must be smaller than, or equal
 *	    to, startbit.
 * @pbuflen: The length in bytes of the packed buffer pointed to by @pbuf.
 * @op: If PACK, then uval will be treated as const pointer and copied (packed)
 *	into pbuf, between startbit and endbit.
 *	If UNPACK, then pbuf will be treated as const pointer and the logical
 *	value between startbit and endbit will be copied (unpacked) to uval.
 * @quirks: A bit mask of QUIRK_LITTLE_ENDIAN, QUIRK_LSW32_IS_FIRST and
 *	    QUIRK_MSB_ON_THE_RIGHT.
 *
 * Return: 0 on success, EINVAL or ERANGE if called incorrectly. Assuming
 *	   correct usage, return code may be discarded.
 *	   If op is PACK, pbuf is modified.
 *	   If op is UNPACK, uval is modified.
 */
int packing(void *pbuf, u64 *uval, int startbit, int endbit, size_t pbuflen,
	    enum packing_op op, u8 quirks)
{
	/* Number of bits for storing "uval"
	 * also width of the field to access in the pbuf
	 */
	u64 value_width;
	/* Logical byte indices corresponding to the
	 * start and end of the field.
	 */
	int plogical_first_u8, plogical_last_u8, box;

	/* startbit is expected to be larger than endbit */
	if (startbit < endbit)
		/* Invalid function call */
		return -EINVAL;

	value_width = startbit - endbit + 1;
	if (value_width > 64)
		return -ERANGE;

	/* Check if "uval" fits in "value_width" bits.
	 * If value_width is 64, the check will fail, but any
	 * 64-bit uval will surely fit.
	 */
	if (op == PACK && value_width < 64 && (*uval >= (1ull << value_width)))
		/* Cannot store "uval" inside "value_width" bits.
		 * Truncating "uval" is most certainly not desirable,
		 * so simply erroring out is appropriate.
		 */
		return -ERANGE;

	/* Initialize parameter */
	if (op == UNPACK)
		*uval = 0;

	/* Iterate through an idealistic view of the pbuf as an u64 with
	 * no quirks, u8 by u8 (aligned at u8 boundaries), from high to low
	 * logical bit significance. "box" denotes the current logical u8.
	 */
	plogical_first_u8 = startbit / 8;
	plogical_last_u8  = endbit / 8;

	for (box = plogical_first_u8; box >= plogical_last_u8; box--) {
		/* Bit indices into the currently accessed 8-bit box */
		int box_start_bit, box_end_bit, box_addr;
		u8  box_mask;
		/* Corresponding bits from the unpacked u64 parameter */
		int proj_start_bit, proj_end_bit;
		u64 proj_mask;

		/* This u8 may need to be accessed in its entirety
		 * (from bit 7 to bit 0), or not, depending on the
		 * input arguments startbit and endbit.
		 */
		if (box == plogical_first_u8)
			box_start_bit = startbit % 8;
		else
			box_start_bit = 7;
		if (box == plogical_last_u8)
			box_end_bit = endbit % 8;
		else
			box_end_bit = 0;

		/* We have determined the box bit start and end.
		 * Now we calculate where this (masked) u8 box would fit
		 * in the unpacked (CPU-readable) u64 - the u8 box's
		 * projection onto the unpacked u64. Though the
		 * box is u8, the projection is u64 because it may fall
		 * anywhere within the unpacked u64.
		 */
		proj_start_bit = ((box * 8) + box_start_bit) - endbit;
		proj_end_bit   = ((box * 8) + box_end_bit) - endbit;
		proj_mask = GENMASK_ULL(proj_start_bit, proj_end_bit);
		box_mask  = GENMASK_ULL(box_start_bit, box_end_bit);

		/* Determine the offset of the u8 box inside the pbuf,
		 * adjusted for quirks. The adjusted box_addr will be used for
		 * effective addressing inside the pbuf (so it's not
		 * logical any longer).
		 */
		box_addr = pbuflen - box - 1;
		if (quirks & QUIRK_LITTLE_ENDIAN)
			box_addr = get_le_offset(box_addr);
		if (quirks & QUIRK_LSW32_IS_FIRST)
			box_addr = get_reverse_lsw32_offset(box_addr,
							    pbuflen);

		if (op == UNPACK) {
			u64 pval;

			/* Read from pbuf, write to uval */
			pval = ((u8 *)pbuf)[box_addr] & box_mask;
			if (quirks & QUIRK_MSB_ON_THE_RIGHT)
				adjust_for_msb_right_quirk(&pval,
							   &box_start_bit,
							   &box_end_bit,
							   &box_mask);

			pval >>= box_end_bit;
			pval <<= proj_end_bit;
			*uval &= ~proj_mask;
			*uval |= pval;
		} else {
			u64 pval;

			/* Write to pbuf, read from uval */
			pval = (*uval) & proj_mask;
			pval >>= proj_end_bit;
			if (quirks & QUIRK_MSB_ON_THE_RIGHT)
				adjust_for_msb_right_quirk(&pval,
							   &box_start_bit,
							   &box_end_bit,
							   &box_mask);

			pval <<= box_end_bit;
			((u8 *)pbuf)[box_addr] &= ~box_mask;
			((u8 *)pbuf)[box_addr] |= pval;
		}
	}
	return 0;
}
EXPORT_SYMBOL(packing);

MODULE_DESCRIPTION("Generic bitfield packing and unpacking");
Commit	Line	Data
554aae35	1	// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
3c9cfb52	2	/* Copyright 2016-2018 NXP
554aae35 VO	3	* Copyright (c) 2018-2019, Vladimir Oltean <[email protected]>
	4	*/
	5	#include <linux/packing.h>
	6	#include <linux/module.h>
	7	#include <linux/bitops.h>
	8	#include <linux/errno.h>
	9	#include <linux/types.h>
1280d4b7	10	#include <linux/bitrev.h>
554aae35 VO	11
	12	static int get_le_offset(int offset)
	13	{
	14	int closest_multiple_of_4;
	15
	16	closest_multiple_of_4 = (offset / 4) * 4;
	17	offset -= closest_multiple_of_4;
	18	return closest_multiple_of_4 + (3 - offset);
	19	}
	20
	21	static int get_reverse_lsw32_offset(int offset, size_t len)
	22	{
	23	int closest_multiple_of_4;
	24	int word_index;
	25
	26	word_index = offset / 4;
	27	closest_multiple_of_4 = word_index * 4;
	28	offset -= closest_multiple_of_4;
	29	word_index = (len / 4) - word_index - 1;
	30	return word_index * 4 + offset;
	31	}
	32
554aae35 VO	33	static void adjust_for_msb_right_quirk(u64 to_write, int box_start_bit,
	34	int box_end_bit, u8 box_mask)
	35	{
	36	int box_bit_width = box_start_bit - box_end_bit + 1;
	37	int new_box_start_bit, new_box_end_bit;
	38
	39	to_write >>= box_end_bit;
1280d4b7	40	to_write = bitrev8(to_write) >> (8 - box_bit_width);
554aae35 VO	41	to_write <<= box_end_bit;
	42
	43	new_box_end_bit = box_bit_width - *box_start_bit - 1;
	44	new_box_start_bit = box_bit_width - *box_end_bit - 1;
	45	*box_mask = GENMASK_ULL(new_box_start_bit, new_box_end_bit);
	46	*box_start_bit = new_box_start_bit;
	47	*box_end_bit = new_box_end_bit;
	48	}
	49
	50	/**
	51	* packing - Convert numbers (currently u64) between a packed and an unpacked
	52	* format. Unpacked means laid out in memory in the CPU's native
	53	* understanding of integers, while packed means anything else that
	54	* requires translation.
	55	*
	56	* @pbuf: Pointer to a buffer holding the packed value.
	57	* @uval: Pointer to an u64 holding the unpacked value.
	58	* @startbit: The index (in logical notation, compensated for quirks) where
	59	* the packed value starts within pbuf. Must be larger than, or
	60	* equal to, endbit.
	61	* @endbit: The index (in logical notation, compensated for quirks) where
	62	* the packed value ends within pbuf. Must be smaller than, or equal
	63	* to, startbit.
7dea927f	64	* @pbuflen: The length in bytes of the packed buffer pointed to by @pbuf.
554aae35 VO	65	* @op: If PACK, then uval will be treated as const pointer and copied (packed)
	66	* into pbuf, between startbit and endbit.
	67	* If UNPACK, then pbuf will be treated as const pointer and the logical
	68	* value between startbit and endbit will be copied (unpacked) to uval.
	69	* @quirks: A bit mask of QUIRK_LITTLE_ENDIAN, QUIRK_LSW32_IS_FIRST and
	70	* QUIRK_MSB_ON_THE_RIGHT.
	71	*
	72	* Return: 0 on success, EINVAL or ERANGE if called incorrectly. Assuming
	73	* correct usage, return code may be discarded.
	74	* If op is PACK, pbuf is modified.
	75	* If op is UNPACK, uval is modified.
	76	*/
	77	int packing(void pbuf, u64 uval, int startbit, int endbit, size_t pbuflen,
	78	enum packing_op op, u8 quirks)
	79	{
	80	/* Number of bits for storing "uval"
	81	* also width of the field to access in the pbuf
	82	*/
	83	u64 value_width;
	84	/* Logical byte indices corresponding to the
	85	* start and end of the field.
	86	*/
	87	int plogical_first_u8, plogical_last_u8, box;
	88
	89	/* startbit is expected to be larger than endbit */
	90	if (startbit < endbit)
	91	/* Invalid function call */
	92	return -EINVAL;
	93
	94	value_width = startbit - endbit + 1;
	95	if (value_width > 64)
	96	return -ERANGE;
	97
	98	/* Check if "uval" fits in "value_width" bits.
	99	* If value_width is 64, the check will fail, but any
	100	* 64-bit uval will surely fit.
	101	*/
	102	if (op == PACK && value_width < 64 && (*uval >= (1ull << value_width)))
	103	/* Cannot store "uval" inside "value_width" bits.
	104	* Truncating "uval" is most certainly not desirable,
	105	* so simply erroring out is appropriate.
	106	*/
	107	return -ERANGE;
	108
	109	/* Initialize parameter */
	110	if (op == UNPACK)
	111	*uval = 0;
	112
	113	/* Iterate through an idealistic view of the pbuf as an u64 with
	114	* no quirks, u8 by u8 (aligned at u8 boundaries), from high to low
	115	* logical bit significance. "box" denotes the current logical u8.
	116	*/
	117	plogical_first_u8 = startbit / 8;
	118	plogical_last_u8 = endbit / 8;
	119
	120	for (box = plogical_first_u8; box >= plogical_last_u8; box--) {
	121	/* Bit indices into the currently accessed 8-bit box */
	122	int box_start_bit, box_end_bit, box_addr;
	123	u8 box_mask;
	124	/* Corresponding bits from the unpacked u64 parameter */
	125	int proj_start_bit, proj_end_bit;
	126	u64 proj_mask;
	127
	128	/* This u8 may need to be accessed in its entirety
129	* (from bit 7 to bit 0), or not, depending on the
130	* input arguments startbit and endbit.
131	*/
132	if (box == plogical_first_u8)
133	box_start_bit = startbit % 8;
134	else
135	box_start_bit = 7;
136	if (box == plogical_last_u8)
137	box_end_bit = endbit % 8;
138	else
139	box_end_bit = 0;
140
141	/* We have determined the box bit start and end.
142	* Now we calculate where this (masked) u8 box would fit
143	* in the unpacked (CPU-readable) u64 - the u8 box's
144	* projection onto the unpacked u64. Though the
145	* box is u8, the projection is u64 because it may fall
146	* anywhere within the unpacked u64.
147	*/
148	proj_start_bit = ((box * 8) + box_start_bit) - endbit;
149	proj_end_bit = ((box * 8) + box_end_bit) - endbit;
150	proj_mask = GENMASK_ULL(proj_start_bit, proj_end_bit);
151	box_mask = GENMASK_ULL(box_start_bit, box_end_bit);
152
153	/* Determine the offset of the u8 box inside the pbuf,
154	* adjusted for quirks. The adjusted box_addr will be used for
155	* effective addressing inside the pbuf (so it's not
156	* logical any longer).
157	*/
158	box_addr = pbuflen - box - 1;
159	if (quirks & QUIRK_LITTLE_ENDIAN)
160	box_addr = get_le_offset(box_addr);
161	if (quirks & QUIRK_LSW32_IS_FIRST)
162	box_addr = get_reverse_lsw32_offset(box_addr,
163	pbuflen);
164
165	if (op == UNPACK) {
166	u64 pval;
167
168	/* Read from pbuf, write to uval */
169	pval = ((u8 *)pbuf)[box_addr] & box_mask;
170	if (quirks & QUIRK_MSB_ON_THE_RIGHT)
171	adjust_for_msb_right_quirk(&pval,
172	&box_start_bit,
173	&box_end_bit,
174	&box_mask);
175
176	pval >>= box_end_bit;
177	pval <<= proj_end_bit;
178	*uval &= ~proj_mask;
179	*uval \|= pval;
180	} else {
181	u64 pval;
182
183	/* Write to pbuf, read from uval */
184	pval = (*uval) & proj_mask;
185	pval >>= proj_end_bit;
186	if (quirks & QUIRK_MSB_ON_THE_RIGHT)
187	adjust_for_msb_right_quirk(&pval,
188	&box_start_bit,
189	&box_end_bit,
190	&box_mask);
191
192	pval <<= box_end_bit;
193	((u8 *)pbuf)[box_addr] &= ~box_mask;
194	((u8 *)pbuf)[box_addr] \|= pval;
195	}
196	}
197	return 0;
198	}
199	EXPORT_SYMBOL(packing);
200
554aae35	201	MODULE_DESCRIPTION("Generic bitfield packing and unpacking");