ad081e698a
Implements a custom std::streambuf to avoid creating temporary std::string objects and thus optimizing image decode. Suggested by @artemp in https://github.com/mapbox/mapbox-gl-native/pull/5417#issuecomment-227700063.
56 lines
1.5 KiB
C++
56 lines
1.5 KiB
C++
#pragma once
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#include <streambuf>
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namespace mbgl {
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namespace util {
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// ref https://artofcode.wordpress.com/2010/12/12/deriving-from-stdstreambuf/
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class CharArrayBuffer : public std::streambuf
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{
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public:
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CharArrayBuffer(char const* data, std::size_t size)
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: begin_(data), end_(data + size), current_(data) {}
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private:
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int_type underflow() final {
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if (current_ == end_) {
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return traits_type::eof();
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}
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return traits_type::to_int_type(*current_);
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}
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int_type uflow() final {
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if (current_ == end_) {
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return traits_type::eof();
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}
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return traits_type::to_int_type(*current_++);
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}
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int_type pbackfail(int_type ch) final {
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if (current_ == begin_ || (ch != traits_type::eof() && ch != current_[-1])) {
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return traits_type::eof();
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}
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return traits_type::to_int_type(*--current_);
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}
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std::streamsize showmanyc() final {
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return end_ - current_;
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}
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pos_type seekoff(off_type off, std::ios_base::seekdir dir, std::ios_base::openmode) final {
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if (dir == std::ios_base::beg) current_ = std::min(begin_ + off, end_);
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else if (dir == std::ios_base::cur) current_ = std::min(current_ + off, end_);
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else current_ = std::max(end_ - off, begin_); // dir == std::ios_base::end
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return pos_type(off_type(current_ - begin_));
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}
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char const * const begin_;
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char const * const end_;
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char const * current_;
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};
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} // namespace util
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} // namespace mbgl
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