Optimize Delaylines: block-process (not one sample at a time)

This also tweaks fade behavior when the latency changes to prefer a
x-fade when possible.

This new variant does not support concurrent re-allocation and
execution. Hence the auto-connect thread needs to take a lock before
updating latencies (actually there's no need for an explicit update with
built-in backends, so this case remains to be updated further)

1 files changed, 231 insertions, 214 deletions

diff --git a/libs/ardour/delayline.cc b/libs/ardour/delayline.cc
index 19ef460fd0..d0a691c5ff 100644
--- a/libs/ardour/delayline.cc
+++ b/libs/ardour/delayline.cc
@@ -22,11 +22,12 @@
 
 #include "pbd/compose.h"
 
-#include "ardour/debug.h"
 #include "ardour/audio_buffer.h"
-#include "ardour/midi_buffer.h"
 #include "ardour/buffer_set.h"
+#include "ardour/debug.h"
 #include "ardour/delayline.h"
+#include "ardour/midi_buffer.h"
+#include "ardour/runtime_functions.h"
 
 using namespace std;
 using namespace PBD;
@@ -34,13 +35,12 @@ using namespace ARDOUR;
 
 DelayLine::DelayLine (Session& s, const std::string& name)
     : Processor (s, string_compose ("latcomp-%1-%2", name, this))
-		, _delay(0)
-		, _pending_delay(0)
-		, _bsiz(0)
-		, _pending_bsiz(0)
-		, _roff(0)
-		, _woff(0)
-		, _pending_flush(false)
+		, _bsiz (0)
+		, _delay (0)
+		, _pending_delay (0)
+		, _roff (0)
+		, _woff (0)
+		, _pending_flush (false)
 {
 }
 
@@ -54,188 +54,158 @@ DelayLine::set_name (const string& name)
 	return Processor::set_name (string_compose ("latcomp-%1-%2", name, this));
 }
 
-#define FADE_LEN (16)
+#define FADE_LEN (128)
+
 void
-DelayLine::run (BufferSet& bufs, samplepos_t /* start_sample */, samplepos_t /* end_sample */, double /* speed */, pframes_t nsamples, bool)
+DelayLine::run (BufferSet& bufs, samplepos_t /* start_sample */, samplepos_t /* end_sample */, double /* speed */, pframes_t n_samples, bool)
 {
-	const uint32_t chn = _configured_output.n_audio();
-	pframes_t p0 = 0;
-	uint32_t c;
+#ifndef NDEBUG
+	Glib::Threads::Mutex::Lock lm (_set_delay_mutex, Glib::Threads::TRY_LOCK);
+	assert (lm.locked ());
+#endif
 
 	const sampleoffset_t pending_delay = _pending_delay;
-	const sampleoffset_t delay_diff = _delay - pending_delay;
+	sampleoffset_t delay_diff = _delay - pending_delay;
 	const bool pending_flush = _pending_flush;
 	_pending_flush = false;
 
-	/* run() and set_delay() may be called in parallel by
-	 * different threads.
-	 * if a larger buffer is needed, it is allocated in
-	 * set_delay(), here it is just swap'ed in place
-	 */
-	if (_pending_bsiz) {
-		assert(_pending_bsiz >= _bsiz);
-
-		const size_t boff = _pending_bsiz - _bsiz;
-		if (_bsiz > 0) {
-			/* write offset is retained. copy existing data to new buffer */
-			sampleoffset_t wl = _bsiz - _woff;
-			memcpy(_pending_buf.get(), _buf.get(), sizeof(Sample) * _woff * chn);
-			memcpy(_pending_buf.get() + (_pending_bsiz - wl) * chn, _buf.get() + _woff * chn, sizeof(Sample) * wl * chn);
-
-			/* new buffer is all zero by default, fade into the existing data copied above */
-			sampleoffset_t wo = _pending_bsiz - wl;
-			for (pframes_t pos = 0; pos < FADE_LEN; ++pos) {
-				const gain_t gain = (gain_t)pos / (gain_t)FADE_LEN;
-				for (c = 0; c < _configured_output.n_audio(); ++c) {
-					_pending_buf.get()[ wo * chn + c ] *= gain;
-					wo = (wo + 1) % (_pending_bsiz + 1);
+	/* Audio buffers */
+	if (_buf.size () == bufs.count ().n_audio () && _buf.size () > 0) {
+
+		/* handle delay-changes first */
+		if (delay_diff < 0) {
+			/* delay increases: fade out, insert silence, fade-in */
+			const samplecnt_t fade_in_len = std::min (n_samples, (pframes_t)FADE_LEN);
+			samplecnt_t fade_out_len;
+
+			if (_delay < FADE_LEN) {
+				/* if old delay was 0 or smaller than new-delay, add some data to fade.
+				 * Add at most (FADE_LEN - _delay) samples, but no more than -delay_diff
+				 */
+				samplecnt_t add = std::min ((samplecnt_t)FADE_LEN - _delay, (samplecnt_t) -delay_diff);
+				fade_out_len = std::min (_delay + add, (samplecnt_t)FADE_LEN);
+
+				if (add > 0) {
+					AudioDlyBuf::iterator bi = _buf.begin ();
+					for (BufferSet::audio_iterator i = bufs.audio_begin (); i != bufs.audio_end (); ++i, ++bi) {
+						Sample* rb = (*bi).get ();
+						write_to_rb (rb, i->data (), add);
+					}
+					_woff = (_woff + add) % _bsiz;
+					delay_diff += add;
 				}
+			} else {
+				fade_out_len = FADE_LEN;
 			}
 
-			/* read-pointer will be moved and may up anywhere..
-			 * copy current data for smooth fade-out below
-			 */
-			sampleoffset_t roold = _roff;
-			sampleoffset_t ro = _roff;
-			if (ro > _woff) {
-				ro += boff;
-			}
-			ro += delay_diff;
-			if (ro < 0) {
-				ro -= (_pending_bsiz + 1) * floor(ro / (float)(_pending_bsiz + 1));
-			}
-			ro = ro % (_pending_bsiz + 1);
-			for (pframes_t pos = 0; pos < FADE_LEN; ++pos) {
-				for (c = 0; c < _configured_output.n_audio(); ++c) {
-					_pending_buf.get()[ ro * chn + c ] = _buf.get()[ roold * chn + c ];
+			/* fade-out, end of previously written data */
+			for (AudioDlyBuf::iterator i = _buf.begin(); i != _buf.end (); ++i) {
+				Sample* rb = (*i).get ();
+				for (uint32_t s = 0; s < fade_out_len; ++s) {
+					sampleoffset_t off = (_woff + _bsiz - s) % _bsiz;
+					rb[off] *= s / (float) fade_out_len;
 				}
-				ro = (ro + 1) % (_pending_bsiz + 1);
-				roold = (roold + 1) % (_bsiz + 1);
-			}
-		}
-
-		if (_roff > _woff) {
-			_roff += boff;
-		}
-
-		// use shared_array::swap() ??
-		_buf = _pending_buf;
-		_bsiz = _pending_bsiz;
-		_pending_bsiz = 0;
-		_pending_buf.reset();
-	}
-
-	/* there may be no buffer when delay == 0.
-	 * we also need to check audio-channels in case all audio-channels
-	 * were removed in which case no new buffer was allocated. */
-	Sample *buf = _buf.get();
-	if (buf && _configured_output.n_audio() > 0) {
-
-		assert (_bsiz >= pending_delay);
-		const samplecnt_t rbs = _bsiz + 1;
-
-		if (pending_delay != _delay || pending_flush) {
-			const pframes_t fade_len = (nsamples >= FADE_LEN) ? FADE_LEN : nsamples / 2;
-
-			DEBUG_TRACE (DEBUG::LatencyCompensation,
-					string_compose ("Old %1 delay: %2 bufsiz: %3 offset-diff: %4 write-offset: %5 read-offset: %6\n",
-						name(), _delay, _bsiz, ((_woff - _roff + rbs) % rbs), _woff, _roff));
-
-			// fade out at old position
-			c = 0;
-			for (BufferSet::audio_iterator i = bufs.audio_begin(); i != bufs.audio_end() && c <= chn; ++i, ++c) {
-				Sample * const data = i->data();
-				sampleoffset_t roff = _roff;
-				sampleoffset_t woff = _woff;
-				for (pframes_t pos = 0; pos < fade_len; ++pos) {
-					const gain_t gain = (gain_t)(fade_len - pos) / (gain_t)fade_len;
-					buf[ woff * chn + c ] = data[ pos ];
-					data[ pos ] = buf[ roff * chn + c ] * gain;
-					roff = (roff + 1) % rbs;
-					woff = (woff + 1) % rbs;
+				/* clear data in rb */
+				// TODO optimize this using memset
+				for (uint32_t s = 0; s < -delay_diff; ++s) {
+					sampleoffset_t off = (_woff + _bsiz + s) % _bsiz;
+					rb[off] = 0.f;
 				}
 			}
-			_roff = (_roff + fade_len) % rbs;
-			_woff = (_woff + fade_len) % rbs;
 
-			if (pending_flush) {
-				DEBUG_TRACE (DEBUG::LatencyCompensation,
-						string_compose ("Flush buffer: %1\n", name()));
-				memset(buf, 0, _configured_output.n_audio() * rbs * sizeof (Sample));
-			}
-
-			// adjust read pointer
-			_roff += _delay - pending_delay;
+			_woff = (_woff - delay_diff) % _bsiz;
 
-			if (_roff < 0) {
-				_roff -= rbs * floor(_roff / (float)rbs);
+			/* fade-in, directly apply to input buffer */
+			for (BufferSet::audio_iterator i = bufs.audio_begin (); i != bufs.audio_end (); ++i) {
+				Sample* src = i->data ();
+				for (uint32_t s = 0; s < fade_in_len; ++s) {
+					src[s] *= s / (float) fade_in_len;
+				}
 			}
-			_roff = _roff % rbs;
-
-			// fade in at new position
-			c = 0;
-			for (BufferSet::audio_iterator i = bufs.audio_begin(); i != bufs.audio_end() && c <= chn; ++i, ++c) {
-				Sample * const data = i->data();
-				sampleoffset_t roff = _roff;
-				sampleoffset_t woff = _woff;
-				for (pframes_t pos = fade_len; pos < 2 * fade_len; ++pos) {
-					const gain_t gain = (gain_t)(pos - fade_len) / (gain_t)fade_len;
-					buf[ woff * chn + c ] = data[ pos ];
-					data[ pos ] = buf[ roff * chn + c ] * gain;
-					roff = (roff + 1) % rbs;
-					woff = (woff + 1) % rbs;
+		} else if (delay_diff > 0) {
+			/* delay decreases: cross-fade, if possible */
+			const samplecnt_t fade_out_len = std::min (_delay, (samplecnt_t)FADE_LEN);
+			const samplecnt_t fade_in_len = std::min (n_samples, (pframes_t)FADE_LEN);
+			const samplecnt_t xfade_len = std::min (fade_out_len, fade_in_len);
+
+			AudioDlyBuf::iterator bi = _buf.begin ();
+			for (BufferSet::audio_iterator i = bufs.audio_begin (); i != bufs.audio_end (); ++i, ++bi) {
+				Sample* rb = (*bi).get ();
+				Sample* src = i->data ();
+
+				// TODO consider handling fade_out & fade_in separately
+				// if fade_out_len < fade_in_len.
+				for (uint32_t s = 0; s < xfade_len; ++s) {
+					sampleoffset_t off = (_roff + s) % _bsiz;
+					const gain_t g = s / (float) xfade_len;
+					src[s] *= g;
+					src[s] += (1.f - g) * rb[off];
 				}
 			}
-			_roff = (_roff + fade_len) % rbs;
-			_woff = (_woff + fade_len) % rbs;
-			p0  = 2 * fade_len;
-
-			_delay = pending_delay;
 
-			DEBUG_TRACE (DEBUG::LatencyCompensation,
-					string_compose ("New %1 delay: %2 bufsiz: %3 offset-diff: %4 write-offset: %5 read-offset: %6\n",
-						name(), _delay, _bsiz, ((_woff - _roff + rbs) % rbs), _woff, _roff));
+#ifndef NDEBUG
+			sampleoffset_t check = (_roff + delay_diff) % _bsiz;
+#endif
+			_roff = (_woff + _bsiz - pending_delay) % _bsiz;
+#ifndef NDEBUG
+			assert (_roff == check);
+#endif
 		}
 
-		assert(_delay == ((_woff - _roff + rbs) % rbs));
-
-		c = 0;
-		for (BufferSet::audio_iterator i = bufs.audio_begin(); i != bufs.audio_end() && c <= chn; ++i, ++c) {
-			Sample * const data = i->data();
-			sampleoffset_t roff = _roff;
-			sampleoffset_t woff = _woff;
-			for (pframes_t pos = p0; pos < nsamples; ++pos) {
-				buf[ woff * chn + c ] = data[ pos ];
-				data[ pos ] = buf[ roff * chn + c ];
-				roff = (roff + 1) % rbs;
-				woff = (woff + 1) % rbs;
+		/* set new delay */
+		_delay = pending_delay;
+
+		/* delay audio buffers */
+		assert (_delay == ((_woff - _roff + _bsiz) % _bsiz));
+		AudioDlyBuf::iterator bi = _buf.begin ();
+		if (_delay == 0) {
+			/* do nothing */
+		} else if (n_samples <= _delay) {
+			/* write all samples to rb, read all from rb */
+			for (BufferSet::audio_iterator i = bufs.audio_begin (); i != bufs.audio_end (); ++i, ++bi) {
+				Sample* rb = (*bi).get ();
+				write_to_rb (rb, i->data (), n_samples);
+				read_from_rb (rb, i->data (), n_samples);
+			}
+			_roff = (_roff + n_samples) % _bsiz;
+			_woff = (_woff + n_samples) % _bsiz;
+		} else {
+			/* only write _delay samples to ringbuffer, memmove buffer */
+			samplecnt_t tail = n_samples - _delay;
+			for (BufferSet::audio_iterator i = bufs.audio_begin (); i != bufs.audio_end (); ++i, ++bi) {
+				Sample* rb = (*bi).get ();
+				Sample* src = i->data ();
+				write_to_rb (rb, &src[tail], _delay);
+				memmove (&src[_delay], src, tail * sizeof(Sample));
+				read_from_rb (rb, src, _delay);
 			}
+			_roff = (_roff + _delay) % _bsiz;
+			_woff = (_woff + _delay) % _bsiz;
 		}
-		_roff = (_roff + nsamples) % rbs;
-		_woff = (_woff + nsamples) % rbs;
-	}
-
-	if (_midi_buf.get()) {
+	} else {
+		/* set new delay for MIDI only */
 		_delay = pending_delay;
+	}
 
-		for (BufferSet::midi_iterator i = bufs.midi_begin(); i != bufs.midi_end(); ++i) {
-			if (i != bufs.midi_begin()) { break; } // XXX only one buffer for now
+	if (_midi_buf.get ()) {
+		for (BufferSet::midi_iterator i = bufs.midi_begin (); i != bufs.midi_end (); ++i) {
+			if (i != bufs.midi_begin ()) { break; } // XXX only one buffer for now
 
-			MidiBuffer* dly = _midi_buf.get();
+			MidiBuffer* dly = _midi_buf.get ();
 			MidiBuffer& mb (*i);
 			if (pending_flush) {
-				dly->silence(nsamples);
+				dly->silence (n_samples);
 			}
 
 			// If the delay time changes, iterate over all events in the dly-buffer
 			// and adjust the time in-place. <= 0 becomes 0.
 			//
 			// iterate over all events in dly-buffer and subtract one cycle
-			// (nsamples) from the timestamp, bringing them closer to de-queue.
-			for (MidiBuffer::iterator m = dly->begin(); m != dly->end(); ++m) {
-				MidiBuffer::TimeType *t = m.timeptr();
-				if (*t > nsamples + delay_diff) {
-					*t -= nsamples + delay_diff;
+			// (n_samples) from the timestamp, bringing them closer to de-queue.
+			for (MidiBuffer::iterator m = dly->begin (); m != dly->end (); ++m) {
+				MidiBuffer::TimeType *t = m.timeptr ();
+				if (*t > n_samples + delay_diff) {
+					*t -= n_samples + delay_diff;
 				} else {
 					*t = 0;
 				}
@@ -243,21 +213,21 @@ DelayLine::run (BufferSet& bufs, samplepos_t /* start_sample */, samplepos_t /*
 
 			if (_delay != 0) {
 				// delay events in current-buffer, in place.
-				for (MidiBuffer::iterator m = mb.begin(); m != mb.end(); ++m) {
-					MidiBuffer::TimeType *t = m.timeptr();
+				for (MidiBuffer::iterator m = mb.begin (); m != mb.end (); ++m) {
+					MidiBuffer::TimeType *t = m.timeptr ();
 					*t += _delay;
 				}
 			}
 
-			// move events from dly-buffer into current-buffer until nsamples
+			// move events from dly-buffer into current-buffer until n_samples
 			// and remove them from the dly-buffer
-			for (MidiBuffer::iterator m = dly->begin(); m != dly->end();) {
+			for (MidiBuffer::iterator m = dly->begin (); m != dly->end ();) {
 				const Evoral::Event<MidiBuffer::TimeType> ev (*m, false);
-				if (ev.time() >= nsamples) {
+				if (ev.time () >= n_samples) {
 					break;
 				}
-				mb.insert_event(ev);
-				m = dly->erase(m);
+				mb.insert_event (ev);
+				m = dly->erase (m);
 			}
 
 			/* For now, this is only relevant if there is there's a positive delay.
@@ -265,27 +235,30 @@ DelayLine::run (BufferSet& bufs, samplepos_t /* start_sample */, samplepos_t /*
 			 * (ie '_global_port_buffer_offset + _port_buffer_offset' - midi_port.cc)
 			 */
 			if (_delay != 0) {
-				// move events after nsamples from current-buffer into dly-buffer
-				// and trim current-buffer after nsamples
-				for (MidiBuffer::iterator m = mb.begin(); m != mb.end();) {
+				// move events after n_samples from current-buffer into dly-buffer
+				// and trim current-buffer after n_samples
+				for (MidiBuffer::iterator m = mb.begin (); m != mb.end ();) {
 					const Evoral::Event<MidiBuffer::TimeType> ev (*m, false);
-					if (ev.time() < nsamples) {
+					if (ev.time () < n_samples) {
 						++m;
 						continue;
 					}
-					dly->insert_event(ev);
-					m = mb.erase(m);
+					dly->insert_event (ev);
+					m = mb.erase (m);
 				}
 			}
 		}
 	}
-
-	_delay = pending_delay;
 }
 
 bool
-DelayLine::set_delay(samplecnt_t signal_delay)
+DelayLine::set_delay (samplecnt_t signal_delay)
 {
+#ifndef NDEBUG
+	Glib::Threads::Mutex::Lock lm (_set_delay_mutex, Glib::Threads::TRY_LOCK);
+	assert (lm.locked ());
+#endif
+
 	if (signal_delay < 0) {
 		signal_delay = 0;
 		cerr << "WARNING: latency compensation is not possible.\n";
@@ -294,36 +267,19 @@ DelayLine::set_delay(samplecnt_t signal_delay)
 	if (signal_delay == _pending_delay) {
 		DEBUG_TRACE (DEBUG::LatencyCompensation,
 				string_compose ("%1 set_delay - no change: %2 samples for %3 channels\n",
-					name(), signal_delay, _configured_output.n_audio()));
+					name (), signal_delay, _configured_output.n_audio ()));
 		return false;
 	}
 
 	DEBUG_TRACE (DEBUG::LatencyCompensation,
 			string_compose ("%1 set_delay to %2 samples for %3 channels\n",
-				name(), signal_delay, _configured_output.n_audio()));
+				name (), signal_delay, _configured_output.n_audio ()));
 
-	if (signal_delay <= _bsiz) {
-		_pending_delay = signal_delay;
-		return true;
+	if (signal_delay + 8192 + 1 > _bsiz) {
+		allocate_pending_buffers (signal_delay, _configured_output);
 	}
 
-	if (_pending_bsiz) {
-		if (_pending_bsiz < signal_delay) {
-			cerr << "LatComp: buffer resize in progress. "<< name() << "pending: "<< _pending_bsiz <<" want: " << signal_delay <<"\n"; // XXX
-		} else {
-			_pending_delay = signal_delay;
-		}
-		return true;
-	}
-
-	allocate_pending_buffers (signal_delay);
-
 	_pending_delay = signal_delay;
-
-	DEBUG_TRACE (DEBUG::LatencyCompensation,
-			string_compose ("allocated buffer for %1 of size %2\n",
-				name(), signal_delay));
-
 	return true;
 }
 
@@ -335,51 +291,82 @@ DelayLine::can_support_io_configuration (const ChanCount& in, ChanCount& out)
 }
 
 void
-DelayLine::allocate_pending_buffers (samplecnt_t signal_delay)
+DelayLine::allocate_pending_buffers (samplecnt_t signal_delay, ChanCount const& cc)
 {
 	assert (signal_delay >= 0);
-	const samplecnt_t rbs = signal_delay + 1;
+	samplecnt_t rbs = signal_delay + 8192 + 1;
+	rbs = std::max (_bsiz, rbs);
 
-	if (_configured_output.n_audio() > 0 ) {
-		_pending_buf.reset(new Sample[_configured_output.n_audio() * rbs]);
-		memset(_pending_buf.get(), 0, _configured_output.n_audio() * rbs * sizeof (Sample));
-		_pending_bsiz = signal_delay;
-	} else {
-		_pending_buf.reset();
-		_pending_bsiz = 0;
+	if (cc.n_audio () == _buf.size () && _bsiz == rbs) {
+		return;
+	}
+
+	_buf.clear ();
+	if (cc.n_audio () == 0) {
+		return;
+	}
+
+	AudioDlyBuf pending_buf;
+	for (uint32_t i = 0; i < cc.n_audio (); ++i) {
+		boost::shared_array<Sample> b (new Sample[rbs]);
+		pending_buf.push_back (b);
+		memset (b.get (), 0, rbs * sizeof (Sample));
+	}
+
+	AudioDlyBuf::iterator bo = _buf.begin ();
+	AudioDlyBuf::iterator bn = pending_buf.begin ();
+
+	for (; bo != _buf.end () && bn != pending_buf.end(); ++bo, ++bn) {
+		Sample* rbo = (*bo).get ();
+		Sample* rbn = (*bn).get ();
+		if (_roff < _woff) {
+			/* copy data between _roff .. _woff to new buffer */
+			copy_vector (&rbn[_roff], &rbo[_roff], _woff - _roff);
+		} else {
+			/* copy data between _roff .. old_size to end of new buffer, increment _roff
+			 * copy data from 0.._woff to beginning of new buffer
+			 */
+			sampleoffset_t offset = rbs - _bsiz;
+			copy_vector (&rbn[_roff + offset], &rbo[_roff], _bsiz - _roff);
+			copy_vector (rbn, rbo, _woff);
+			_roff += offset;
+			assert (_roff < rbs);
+		}
 	}
+	_bsiz = rbs;
+	_buf.swap (pending_buf);
 }
 
 bool
 DelayLine::configure_io (ChanCount in, ChanCount out)
 {
+#ifndef NDEBUG
+	Glib::Threads::Mutex::Lock lm (_set_delay_mutex, Glib::Threads::TRY_LOCK);
+	assert (lm.locked ());
+#endif
+
 	if (out != in) { // always 1:1
 		return false;
 	}
 
 	if (_configured_output != out) {
-		// run() won't be called concurrently, so it's
-		// save for replace existing _pending_buf.
-		//
-		// configure_io is either called with process-lock held
-		// from route's configure_io() or by use_target() from the c'tor.
-		allocate_pending_buffers (_pending_delay);
+		allocate_pending_buffers (_pending_delay, out);
 	}
 
 	DEBUG_TRACE (DEBUG::LatencyCompensation,
 			string_compose ("configure IO: %1 Ain: %2 Aout: %3 Min: %4 Mout: %5\n",
-				name(), in.n_audio(), out.n_audio(), in.n_midi(), out.n_midi()));
+				name (), in.n_audio (), out.n_audio (), in.n_midi (), out.n_midi ()));
 
 	// TODO support multiple midi buffers
-	if (in.n_midi() > 0 && !_midi_buf) {
-		_midi_buf.reset(new MidiBuffer(16384));
+	if (in.n_midi () > 0 && !_midi_buf) {
+		_midi_buf.reset (new MidiBuffer (16384));
 	}
 
 	return Processor::configure_io (in, out);
 }
 
 void
-DelayLine::flush()
+DelayLine::flush ()
 {
 	_pending_flush = true;
 }
@@ -388,6 +375,36 @@ XMLNode&
 DelayLine::state ()
 {
 	XMLNode& node (Processor::state ());
-	node.set_property("type", "delay");
+	node.set_property ("type", "delay");
 	return node;
 }
+
+void
+DelayLine::write_to_rb (Sample* rb, Sample* src, samplecnt_t n_samples)
+{
+	assert (n_samples < _bsiz);
+	if (_woff + n_samples < _bsiz) {
+		copy_vector (&rb[_woff], src, n_samples);
+	} else {
+		const samplecnt_t s0 = _bsiz - _woff;
+		const samplecnt_t s1 = n_samples - s0;
+
+		copy_vector (&rb[_woff], src, s0);
+		copy_vector (rb, &src[s0], s1);
+	}
+}
+
+void
+DelayLine::read_from_rb (Sample* rb, Sample* dst, samplecnt_t n_samples)
+{
+	assert (n_samples < _bsiz);
+	if (_roff + n_samples < _bsiz) {
+		copy_vector (dst, &rb[_roff], n_samples);
+	} else {
+		const samplecnt_t s0 = _bsiz - _roff;
+		const samplecnt_t s1 = n_samples - s0;
+
+		copy_vector (dst, &rb[_roff], s0);
+		copy_vector (&dst[s0], rb, s1);
+	}
+}