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/*
* Copyright (C) 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "HidUtils.h"
#include <stdint.h>
#include <algorithm>
namespace HidUtil {
void copyBits(const void *src, void *dst, size_t dst_size,
unsigned int src_bit_offset, unsigned int dst_bit_offset,
unsigned int bit_count) {
const uint8_t *p_src;
uint8_t *p_dst;
uint8_t dst_mask;
unsigned int bits_rem;
unsigned int bit_block_count;
// Do nothing if copying past the end of the destination buffer.
if ((static_cast<size_t>(dst_bit_offset) > (8 * dst_size)) ||
(static_cast<size_t>(bit_count) > (8 * dst_size)) ||
(static_cast<size_t>(dst_bit_offset + bit_count) > (8 * dst_size))) {
return;
}
// Copy bits from source to destination buffer.
p_src = static_cast<const uint8_t*>(src) + (src_bit_offset / 8);
src_bit_offset = src_bit_offset % 8;
p_dst = static_cast<uint8_t*>(dst) + (dst_bit_offset / 8);
dst_bit_offset = dst_bit_offset % 8;
bits_rem = bit_count;
while (bits_rem > 0) {
// Determine the size of the next block of bits to copy. The block must
// not cross a source or desintation byte boundary.
bit_block_count = std::min(bits_rem, 8 - src_bit_offset);
bit_block_count = std::min(bit_block_count, 8 - dst_bit_offset);
// Determine the destination bit block mask.
dst_mask = ((1 << bit_block_count) - 1) << dst_bit_offset;
// Copy the block of bits.
*p_dst = (*p_dst & ~dst_mask) |
(((*p_src >> src_bit_offset) << dst_bit_offset) & dst_mask);
// Advance past the block of copied bits in the source.
src_bit_offset += bit_block_count;
p_src += src_bit_offset / 8;
src_bit_offset = src_bit_offset % 8;
// Advance past the block of copied bits in the destination.
dst_bit_offset += bit_block_count;
p_dst += dst_bit_offset / 8;
dst_bit_offset = dst_bit_offset % 8;
// Decrement the number of bits remaining.
bits_rem -= bit_block_count;
}
}
} // namespace HidUtil
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