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packing.c
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// 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>
/**
* calculate_box_addr - Determine physical location of byte in buffer
* @box: Index of byte within buffer seen as a logical big-endian big number
* @len: Size of buffer in bytes
* @quirks: mask of QUIRK_LSW32_IS_FIRST and QUIRK_LITTLE_ENDIAN
*
* Function interprets the buffer as a @len byte sized big number, and returns
* the physical offset of the @box logical octet within it. Internally, it
* treats the big number as groups of 4 bytes. If @len is not a multiple of 4,
* the last group may be shorter.
*
* @QUIRK_LSW32_IS_FIRST gives the ordering of groups of 4 octets relative to
* each other. If set, the most significant group of 4 octets is last in the
* buffer (and may be truncated if @len is not a multiple of 4).
*
* @QUIRK_LITTLE_ENDIAN gives the ordering of bytes within each group of 4.
* If set, the most significant byte is last in the group. If @len takes the
* form of 4k+3, the last group will only be able to represent 24 bits, and its
* most significant octet is byte 2.
*
* Return: the physical offset into the buffer corresponding to the logical box.
*/
static size_t calculate_box_addr(size_t box, size_t len, u8 quirks)
{
size_t offset_of_group, offset_in_group, this_group = box / 4;
size_t group_size;
if (quirks & QUIRK_LSW32_IS_FIRST)
offset_of_group = this_group * 4;
else
offset_of_group = len - ((this_group + 1) * 4);
group_size = min(4, len - offset_of_group);
if (quirks & QUIRK_LITTLE_ENDIAN)
offset_in_group = box - this_group * 4;
else
offset_in_group = group_size - (box - this_group * 4) - 1;
return offset_of_group + offset_in_group;
}
/**
* pack - Pack u64 number into bitfield of buffer.
*
* @pbuf: Pointer to a buffer holding the packed value.
* @uval: CPU-readable unpacked value to pack.
* @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.
* @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. The @pbuf memory will
* be modified on success.
*/
int pack(void *pbuf, u64 uval, size_t startbit, size_t endbit, size_t pbuflen,
u8 quirks)
{
/* Logical byte indices corresponding to the
* start and end of the field.
*/
int plogical_first_u8, plogical_last_u8, box;
/* width of the field to access in the pbuf */
u64 value_width;
/* startbit is expected to be larger than endbit, and both are
* expected to be within the logically addressable range of the buffer.
*/
if (unlikely(startbit < endbit || startbit >= BITS_PER_BYTE * pbuflen))
/* Invalid function call */
return -EINVAL;
value_width = startbit - endbit + 1;
if (unlikely(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 (unlikely(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;
/* 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 / BITS_PER_BYTE;
plogical_last_u8 = endbit / BITS_PER_BYTE;
for (box = plogical_first_u8; box >= plogical_last_u8; box--) {
/* Bit indices into the currently accessed 8-bit box */
size_t box_start_bit, box_end_bit, box_addr;
u8 box_mask;
/* Corresponding bits from the unpacked u64 parameter */
size_t proj_start_bit, proj_end_bit;
u64 proj_mask;
u64 pval;
/* 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 % BITS_PER_BYTE;
else
box_start_bit = 7;
if (box == plogical_last_u8)
box_end_bit = endbit % BITS_PER_BYTE;
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 * BITS_PER_BYTE) + box_start_bit) - endbit;
proj_end_bit = ((box * BITS_PER_BYTE) + box_end_bit) - endbit;
proj_mask = GENMASK_ULL(proj_start_bit, proj_end_bit);
box_mask = GENMASK(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 = calculate_box_addr(box, pbuflen, quirks);
/* Write to pbuf, read from uval */
pval = uval & proj_mask;
pval >>= proj_end_bit;
pval <<= box_end_bit;
if (quirks & QUIRK_MSB_ON_THE_RIGHT) {
pval = bitrev8(pval);
box_mask = bitrev8(box_mask);
}
((u8 *)pbuf)[box_addr] &= ~box_mask;
((u8 *)pbuf)[box_addr] |= pval;
}
return 0;
}
EXPORT_SYMBOL(pack);
/**
* unpack - Unpack u64 number from packed buffer.
*
* @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.
* @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. The @uval will be
* modified on success.
*/
int unpack(const void *pbuf, u64 *uval, size_t startbit, size_t endbit,
size_t pbuflen, u8 quirks)
{
/* Logical byte indices corresponding to the
* start and end of the field.
*/
int plogical_first_u8, plogical_last_u8, box;
/* width of the field to access in the pbuf */
u64 value_width;
/* startbit is expected to be larger than endbit, and both are
* expected to be within the logically addressable range of the buffer.
*/
if (unlikely(startbit < endbit || startbit >= BITS_PER_BYTE * pbuflen))
/* Invalid function call */
return -EINVAL;
value_width = startbit - endbit + 1;
if (unlikely(value_width > 64))
return -ERANGE;
/* Initialize parameter */
*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 / BITS_PER_BYTE;
plogical_last_u8 = endbit / BITS_PER_BYTE;
for (box = plogical_first_u8; box >= plogical_last_u8; box--) {
/* Bit indices into the currently accessed 8-bit box */
size_t box_start_bit, box_end_bit, box_addr;
u8 box_mask;
/* Corresponding bits from the unpacked u64 parameter */
size_t proj_start_bit, proj_end_bit;
u64 proj_mask;
u64 pval;
/* 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 % BITS_PER_BYTE;
else
box_start_bit = 7;
if (box == plogical_last_u8)
box_end_bit = endbit % BITS_PER_BYTE;
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 * BITS_PER_BYTE) + box_start_bit) - endbit;
proj_end_bit = ((box * BITS_PER_BYTE) + box_end_bit) - endbit;
proj_mask = GENMASK_ULL(proj_start_bit, proj_end_bit);
box_mask = GENMASK(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 = calculate_box_addr(box, pbuflen, quirks);
/* Read from pbuf, write to uval */
pval = ((u8 *)pbuf)[box_addr];
if (quirks & QUIRK_MSB_ON_THE_RIGHT)
pval = bitrev8(pval);
pval &= box_mask;
pval >>= box_end_bit;
pval <<= proj_end_bit;
*uval &= ~proj_mask;
*uval |= pval;
}
return 0;
}
EXPORT_SYMBOL(unpack);
/**
* 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.
*
* Note: this is deprecated, prefer to use pack() or unpack() in new code.
*
* 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)
{
if (op == PACK)
return pack(pbuf, *uval, startbit, endbit, pbuflen, quirks);
return unpack(pbuf, uval, startbit, endbit, pbuflen, quirks);
}
EXPORT_SYMBOL(packing);
MODULE_DESCRIPTION("Generic bitfield packing and unpacking");