33716732a1
Previously, there was no special code to convert stereo to multi-channel. The generic solution for this was to convert to mono, and then copy the result to all channels. That's a pretty bad solution, but at least something which always renders audio. MPD does something, instead of failing. Now that MPD has proper support for multi-channel (by defining the channel order), we can do better than that. It is a (somewhat) common case to play back stereo music on a DAC which can only do multi-channel. The best approach here is to copy the stereo channels to front-left and front-right, and apply the "silence" pattern to all other channels.
222 lines
5.9 KiB
C++
222 lines
5.9 KiB
C++
/*
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* Copyright 2003-2017 The Music Player Daemon Project
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* http://www.musicpd.org
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include "config.h"
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#include "PcmChannels.hxx"
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#include "PcmBuffer.hxx"
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#include "Silence.hxx"
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#include "Traits.hxx"
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#include "AudioFormat.hxx"
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#include "util/ConstBuffer.hxx"
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#include "util/WritableBuffer.hxx"
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#include <array>
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#include <algorithm>
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#include <assert.h>
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template<typename D, typename S>
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static void
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MonoToStereo(D dest, S src, S end)
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{
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while (src != end) {
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const auto value = *src++;
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*dest++ = value;
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*dest++ = value;
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}
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}
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template<SampleFormat F, class Traits=SampleTraits<F>>
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static typename Traits::value_type
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StereoToMono(typename Traits::value_type _a,
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typename Traits::value_type _b)
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{
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typename Traits::sum_type a(_a);
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typename Traits::sum_type b(_b);
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return typename Traits::value_type((a + b) / 2);
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}
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template<SampleFormat F, class Traits=SampleTraits<F>>
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static typename Traits::pointer_type
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StereoToMono(typename Traits::pointer_type dest,
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typename Traits::const_pointer_type src,
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typename Traits::const_pointer_type end)
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{
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while (src != end) {
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const auto a = *src++;
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const auto b = *src++;
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*dest++ = StereoToMono<F, Traits>(a, b);
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}
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return dest;
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}
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template<SampleFormat F, class Traits=SampleTraits<F>>
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static typename Traits::pointer_type
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NToStereo(typename Traits::pointer_type dest,
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unsigned src_channels,
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typename Traits::const_pointer_type src,
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typename Traits::const_pointer_type end)
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{
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assert((end - src) % src_channels == 0);
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while (src != end) {
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typename Traits::sum_type sum = *src++;
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for (unsigned c = 1; c < src_channels; ++c)
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sum += *src++;
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typename Traits::value_type value(sum / int(src_channels));
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/* TODO: this is actually only mono ... */
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*dest++ = value;
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*dest++ = value;
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}
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return dest;
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}
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/**
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* Convert stereo to N channels (where N > 2). Left and right map to
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* the first two channels (front left and front right), and the
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* remaining (surround) channels are filled with silence.
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*/
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template<SampleFormat F, class Traits=SampleTraits<F>>
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static typename Traits::pointer_type
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StereoToN(typename Traits::pointer_type dest,
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unsigned dest_channels,
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typename Traits::const_pointer_type src,
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typename Traits::const_pointer_type end)
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{
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assert(dest_channels > 2);
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assert((end - src) % 2 == 0);
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std::array<typename Traits::value_type, MAX_CHANNELS - 2> silence;
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PcmSilence({&silence.front(), sizeof(silence)}, F);
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while (src != end) {
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/* copy left/right to front-left/front-right, which is
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the first two channels in all multi-channel
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configurations **/
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*dest++ = *src++;
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*dest++ = *src++;
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/* all other channels are silent */
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dest = std::copy_n(silence.begin(), dest_channels - 2, dest);
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}
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return dest;
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}
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template<SampleFormat F, class Traits=SampleTraits<F>>
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static typename Traits::pointer_type
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NToM(typename Traits::pointer_type dest,
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unsigned dest_channels,
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unsigned src_channels,
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typename Traits::const_pointer_type src,
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typename Traits::const_pointer_type end)
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{
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assert((end - src) % src_channels == 0);
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while (src != end) {
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typename Traits::sum_type sum = *src++;
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for (unsigned c = 1; c < src_channels; ++c)
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sum += *src++;
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typename Traits::value_type value(sum / int(src_channels));
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/* TODO: this is actually only mono ... */
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for (unsigned c = 0; c < dest_channels; ++c)
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*dest++ = value;
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}
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return dest;
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}
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template<SampleFormat F, class Traits=SampleTraits<F>>
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static ConstBuffer<typename Traits::value_type>
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ConvertChannels(PcmBuffer &buffer,
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unsigned dest_channels,
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unsigned src_channels,
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ConstBuffer<typename Traits::value_type> src)
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{
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assert(src.size % src_channels == 0);
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const size_t dest_size = src.size / src_channels * dest_channels;
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auto dest = buffer.GetT<typename Traits::value_type>(dest_size);
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if (src_channels == 1 && dest_channels == 2)
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MonoToStereo(dest, src.begin(), src.end());
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else if (src_channels == 2 && dest_channels == 1)
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StereoToMono<F>(dest, src.begin(), src.end());
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else if (dest_channels == 2)
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NToStereo<F>(dest, src_channels, src.begin(), src.end());
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else if (src_channels == 2 && dest_channels > 2)
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StereoToN<F, Traits>(dest, dest_channels,
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src.begin(), src.end());
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else
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NToM<F>(dest, dest_channels,
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src_channels, src.begin(), src.end());
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return { dest, dest_size };
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}
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ConstBuffer<int16_t>
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pcm_convert_channels_16(PcmBuffer &buffer,
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unsigned dest_channels,
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unsigned src_channels,
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ConstBuffer<int16_t> src)
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{
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return ConvertChannels<SampleFormat::S16>(buffer, dest_channels,
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src_channels, src);
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}
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ConstBuffer<int32_t>
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pcm_convert_channels_24(PcmBuffer &buffer,
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unsigned dest_channels,
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unsigned src_channels,
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ConstBuffer<int32_t> src)
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{
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return ConvertChannels<SampleFormat::S24_P32>(buffer, dest_channels,
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src_channels, src);
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}
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ConstBuffer<int32_t>
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pcm_convert_channels_32(PcmBuffer &buffer,
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unsigned dest_channels,
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unsigned src_channels,
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ConstBuffer<int32_t> src)
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{
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return ConvertChannels<SampleFormat::S32>(buffer, dest_channels,
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src_channels, src);
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}
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ConstBuffer<float>
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pcm_convert_channels_float(PcmBuffer &buffer,
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unsigned dest_channels,
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unsigned src_channels,
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ConstBuffer<float> src)
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{
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return ConvertChannels<SampleFormat::FLOAT>(buffer, dest_channels,
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src_channels, src);
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}
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