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/*
* Copyright (c) 2021, Alliance for Open Media. All rights reserved
*
* This source code is subject to the terms of the BSD 3-Clause Clear License
* and the Alliance for Open Media Patent License 1.0. If the BSD 3-Clause Clear
* License was not distributed with this source code in the LICENSE file, you
* can obtain it at aomedia.org/license/software-license/bsd-3-c-c/. If the
* Alliance for Open Media Patent License 1.0 was not distributed with this
* source code in the PATENTS file, you can obtain it at
* aomedia.org/license/patent-license/.
*/
#include <assert.h>
#include "aom/aom_integer.h"
static const size_t kMaximumLeb128Size = 8;
static const uint8_t kLeb128ByteMask = 0x7f; // Binary: 01111111
// Disallow values larger than 32-bits to ensure consistent behavior on 32 and
// 64 bit targets: value is typically used to determine buffer allocation size
// when decoded.
static const uint64_t kMaximumLeb128Value = UINT32_MAX;
size_t aom_uleb_size_in_bytes(uint64_t value) {
size_t size = 0;
do {
++size;
} while ((value >>= 7) != 0);
return size;
}
int aom_uleb_decode(const uint8_t *buffer, size_t available, uint64_t *value,
size_t *length) {
if (buffer && value) {
*value = 0;
for (size_t i = 0; i < kMaximumLeb128Size && i < available; ++i) {
const uint8_t decoded_byte = *(buffer + i) & kLeb128ByteMask;
*value |= ((uint64_t)decoded_byte) << (i * 7);
if ((*(buffer + i) >> 7) == 0) {
if (length) {
*length = i + 1;
}
// Fail on values larger than 32-bits to ensure consistent behavior on
// 32 and 64 bit targets: value is typically used to determine buffer
// allocation size.
if (*value > UINT32_MAX) return -1;
return 0;
}
}
}
// If we get here, either the buffer/value pointers were invalid,
// or we ran over the available space
return -1;
}
int aom_uleb_encode(uint64_t value, size_t available, uint8_t *coded_value,
size_t *coded_size) {
const size_t leb_size = aom_uleb_size_in_bytes(value);
if (value > kMaximumLeb128Value || leb_size > kMaximumLeb128Size ||
leb_size > available || !coded_value || !coded_size) {
return -1;
}
for (size_t i = 0; i < leb_size; ++i) {
uint8_t byte = value & 0x7f;
value >>= 7;
if (value != 0) byte |= 0x80; // Signal that more bytes follow.
*(coded_value + i) = byte;
}
*coded_size = leb_size;
return 0;
}
int aom_uleb_encode_fixed_size(uint64_t value, size_t available,
size_t pad_to_size, uint8_t *coded_value,
size_t *coded_size) {
if (value > kMaximumLeb128Value || !coded_value || !coded_size ||
available < pad_to_size || pad_to_size > kMaximumLeb128Size) {
return -1;
}
const uint64_t limit = 1ULL << (7 * pad_to_size);
if (value >= limit) {
// Can't encode 'value' within 'pad_to_size' bytes
return -1;
}
for (size_t i = 0; i < pad_to_size; ++i) {
uint8_t byte = value & 0x7f;
value >>= 7;
if (i < pad_to_size - 1) byte |= 0x80; // Signal that more bytes follow.
*(coded_value + i) = byte;
}
assert(value == 0);
*coded_size = pad_to_size;
return 0;
}