decompress.hpp

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// SPDX-FileCopyrightText: 2022-2023 Dennis Gläser <dennis.glaeser@iws.uni-stuttgart.de>
// SPDX-License-Identifier: MIT
#ifndef GRIDFORMAT_COMPRESSION_DECOMPRESS_HPP_
#define GRIDFORMAT_COMPRESSION_DECOMPRESS_HPP_
 
#include <string>
 
#include <gridformat/common/exceptions.hpp>
#include <gridformat/common/serialization.hpp>
 
#include <gridformat/compression/concepts.hpp>
#include <gridformat/compression/common.hpp>
 
namespace GridFormat::Compression {

template<std::integral HeaderType, Concepts::BlockDecompressor Decompressor>
void decompress(Serialization& in,
                const CompressedBlocks<HeaderType>& blocks,
                const Decompressor& block_decompressor) {
    using Byte = typename Decompressor::ByteType;
 
    const auto last_block_size = blocks.residual_block_size > 0 ? blocks.residual_block_size : blocks.block_size;
    const auto out_size = blocks.block_size*(blocks.number_of_blocks-1) + last_block_size;
 
    std::size_t in_offset = 0;
    std::size_t out_offset = 0;
    Serialization out{out_size};
 
    const auto* in_data = in.template as_span_of<const Byte>().data();
    auto* out_data = out.template as_span_of<Byte>().data();
    std::ranges::for_each(std::views::iota(HeaderType{0}, blocks.number_of_blocks), [&] (HeaderType i) {
        const auto out_block_size = (i == blocks.number_of_blocks - 1) ? last_block_size : blocks.block_size;
 
        block_decompressor(
            std::span{in_data + in_offset, blocks.compressed_block_sizes[i]},
            std::span{out_data + out_offset, out_block_size}
        );
 
        in_offset += blocks.compressed_block_sizes[i];
        out_offset += out_block_size;
    });
    if (out_offset != out.size())
        throw SizeError(
            "Unexpected number of bytes written: " + std::to_string(out_offset) + " vs. " + std::to_string(out.size())
        );
    in = out;
}
 
}  // end namespace GridFormat::Compression
 
#endif  // GRIDFORMAT_COMPRESSION_DECOMPRESS_HPP_