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// Copyright (c) Meta Platforms, Inc. and affiliates.
// SPDX-License-Identifier: LGPL-2.1-or-later
#include <assert.h>
#include <endian.h>
#include "serialize.h"
static inline uint8_t copy_bits_step(const uint8_t *s, unsigned int src_bit_offset,
unsigned int bit_size,
unsigned int dst_bit_offset, bool lsb0)
{
uint8_t result;
if (lsb0) {
result = s[0] >> src_bit_offset;
if (bit_size > 8 - src_bit_offset)
result |= s[1] << (8 - src_bit_offset);
result <<= dst_bit_offset;
} else {
result = s[0] << src_bit_offset;
if (bit_size > 8 - src_bit_offset)
result |= s[1] >> (8 - src_bit_offset);
result >>= dst_bit_offset;
}
return result;
}
void copy_bits(void *dst, unsigned int dst_bit_offset, const void *src,
unsigned int src_bit_offset, uint64_t bit_size, bool lsb0)
{
assert(dst_bit_offset < 8);
assert(src_bit_offset < 8);
if (bit_size == 0)
return;
uint8_t *d = dst;
const uint8_t *s = src;
uint64_t dst_last_bit = dst_bit_offset + bit_size - 1;
uint8_t dst_first_mask = copy_bits_first_mask(dst_bit_offset, lsb0);
uint8_t dst_last_mask = copy_bits_last_mask(dst_last_bit, lsb0);
if (dst_bit_offset == src_bit_offset) {
/*
* In the common case that the source and destination have the
* same offset, we can use memcpy(), preserving bits at the
* start and/or end if necessary.
*/
uint8_t first_byte = d[0];
uint8_t last_byte = d[dst_last_bit / 8];
memcpy(d, s, dst_last_bit / 8 + 1);
if (dst_bit_offset != 0) {
d[0] = ((first_byte & ~dst_first_mask)
| (d[0] & dst_first_mask));
}
if (dst_last_bit % 8 != 7) {
d[dst_last_bit / 8] = ((last_byte & ~dst_last_mask)
| (d[dst_last_bit / 8] & dst_last_mask));
}
} else if (bit_size <= 8 - dst_bit_offset) {
/* Destination is only one byte. */
uint8_t dst_mask = dst_first_mask & dst_last_mask;
d[0] = ((d[0] & ~dst_mask)
| (copy_bits_step(&s[0], src_bit_offset, bit_size,
dst_bit_offset, lsb0) & dst_mask));
} else {
/* Destination is two or more bytes. */
d[0] = ((d[0] & ~dst_first_mask)
| (copy_bits_step(&s[0], src_bit_offset,
8 - dst_bit_offset, dst_bit_offset,
lsb0) & dst_first_mask));
src_bit_offset += 8 - dst_bit_offset;
size_t si = src_bit_offset / 8;
src_bit_offset %= 8;
size_t di = 1;
while (di < dst_last_bit / 8) {
d[di] = copy_bits_step(&s[si], src_bit_offset, 8, 0,
lsb0);
di++;
si++;
}
d[di] = ((d[di] & ~dst_last_mask)
| (copy_bits_step(&s[si], src_bit_offset,
dst_last_bit % 8 + 1, 0, lsb0)
& dst_last_mask));
}
}
void serialize_bits(void *buf, uint64_t bit_offset, uint64_t uvalue,
uint8_t bit_size, bool little_endian)
{
uint8_t *p;
size_t bits, size;
unsigned char tmp[9];
uint8_t first_mask, last_mask;
assert(bit_size > 0);
assert(bit_size <= 64);
p = (uint8_t *)buf + bit_offset / 8;
bit_offset %= 8;
bits = bit_offset + bit_size;
size = (bits + 7) / 8;
if (little_endian) {
if (size > sizeof(uvalue))
tmp[8] = uvalue >> (64 - bit_offset);
uvalue = htole64(uvalue << bit_offset);
memcpy(tmp, &uvalue, sizeof(uvalue));
/* bit_offset least significant bits. */
first_mask = (1 << bit_offset) - 1;
/* 8 - (bit_offset + bit_size) % 8 most significant bits. */
last_mask = 0xff00 >> -bits % 8;
} else {
unsigned int shift;
shift = -bits % 8;
if (size > sizeof(uvalue)) {
tmp[0] = uvalue >> (64 - shift);
uvalue = htobe64(uvalue << shift);
memcpy(&tmp[1], &uvalue, sizeof(uvalue));
} else {
uvalue = htobe64(uvalue << (64 - bits));
memcpy(&tmp[0], &uvalue, sizeof(uvalue));
}
/* bit_offset most significant bits. */
first_mask = 0xff00 >> bit_offset;
/* 8 - (bit_offset + bit_size) % 8 least significant bits. */
last_mask = (1 << shift) - 1;
}
if (size == 1) {
p[0] = (p[0] & (first_mask | last_mask)) | tmp[0];
} else {
p[0] = (p[0] & first_mask) | tmp[0];
memcpy(p + 1, tmp + 1, size - 2);
p[size - 1] = (p[size - 1] & last_mask) | tmp[size - 1];
}
}
uint64_t deserialize_bits(const void *buf, uint64_t bit_offset,
uint8_t bit_size, bool little_endian)
{
const uint8_t *p;
size_t bits, size;
uint64_t ret = 0;
assert(bit_size > 0);
assert(bit_size <= 64);
p = (const uint8_t *)buf + bit_offset / 8;
bit_offset %= 8;
bits = bit_offset + bit_size;
size = (bits + 7) / 8;
if (little_endian) {
memcpy(&ret, p, min(size, sizeof(ret)));
ret = le64toh(ret) >> bit_offset;
if (size > sizeof(ret))
ret |= (uint64_t)p[8] << (64 - bit_offset);
} else {
unsigned int shift;
if (size > sizeof(ret))
memcpy(&ret, &p[1], sizeof(ret));
else
memcpy((char *)(&ret + 1) - size, p, size);
shift = -bits % 8;
ret = be64toh(ret) >> shift;
if (size > sizeof(ret))
ret |= (uint64_t)p[0] << (64 - shift);
}
return truncate_unsigned(ret, bit_size);
}
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