SerializeBuffer.cc

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#include "SerializeBuffer.hh"
#include <cstdlib>
#include <utility>
 
namespace openmsx {
 
// class OutputBuffer
 
OutputBuffer::OutputBuffer()
        : buf(lastSize)
        , end(buf.data())
{
        // We've allocated a buffer with an estimated initial size. This
        // estimate is based on the largest intermediate size of the previously
        // required buffers.
        // For correctness this initial size doesn't matter (we could even not
        // allocate any initial buffer at all). But it can make a difference in
        // performance. If later we discover the buffer is too small, we have
        // to reallocate (and thus make a copy). In profiling this reallocation
        // step was noticeable.
 
        // Slowly drop the estimated required size. This makes sure that when
        // we've overestimated the size once, we don't forever keep this too
        // high value. For performance an overestimation is less bad than an
        // underestimation.
        lastSize -= lastSize >> 7;
}
 
#ifdef __GNUC__
template<size_t LEN> void OutputBuffer::insertN(const void* __restrict data)
{
        uint8_t* newEnd = end + LEN;
        if (newEnd <= buf.end()) [[likely]] {
                memcpy(end, data, LEN);
                end = newEnd;
        } else {
                insertGrow(data, LEN);
        }
}
// Force template instantiation
template void OutputBuffer::insertN<1>(const void* __restrict data);
template void OutputBuffer::insertN<2>(const void* __restrict data);
template void OutputBuffer::insertN<4>(const void* __restrict data);
template void OutputBuffer::insertN<8>(const void* __restrict data);
#endif
 
void OutputBuffer::insertN(const void* __restrict data, size_t len)
{
        uint8_t* newEnd = end + len;
        if (newEnd <= buf.end()) [[likely]] {
                memcpy(end, data, len);
                end = newEnd;
        } else {
                insertGrow(data, len);
        }
}
 
MemBuffer<uint8_t> OutputBuffer::release() &&
{
        // Deallocate unused buffer space.
        size_t size = end - buf.data();
        buf.resize(size);
 
        end = nullptr;
        return std::move(buf);
}
 
void OutputBuffer::grow(size_t len)
{
        size_t oldSize = end - buf.data();
        size_t newSize = std::max(oldSize + len, oldSize + oldSize / 2);
        buf.resize(newSize);
        end    = buf.data() + oldSize;
}
 
uint8_t* OutputBuffer::allocateGrow(size_t len)
{
        grow(len);
        auto* result = end;
        end += len;
        return result;
}
 
void OutputBuffer::insertGrow(const void* __restrict data, size_t len)
{
        uint8_t* pos = allocateGrow(len);
        memcpy(pos, data, len);
}
 
} // namespace openmsx