Ensure IQ buffer size is a power of two, as required by decimators

plugins/samplesource/usrpinput/usrpinput.cpp

@@ -35,6 +35,7 @@
 #include "device/deviceapi.h"
 #include "dsp/dspcommands.h"
 #include "dsp/dspengine.h"
+#include "util/poweroftwo.h"
 #include "usrpinput.h"
 #include "usrpinputthread.h"
 #include "usrp/deviceusrpparam.h"
@@ -338,8 +339,11 @@ bool USRPInput::acquireChannel()
 
             m_streamId = m_deviceShared.m_deviceParams->getDevice()->get_rx_stream(stream_args);
 
-            // Match our receive buffer size to what UHD uses
+            // Decimators require buffers to sized as powers of two (See #1161)
             m_bufSamples = m_streamId->get_max_num_samps();
+            if (!isPowerOfTwo(m_bufSamples)) {
+                m_bufSamples = lowerPowerOfTwo(m_bufSamples);
+            }
 
             // Wait for reference and LO to lock
             DeviceUSRP::waitForLock(usrp, m_settings.m_clockSource, m_deviceShared.m_channel);

sdrbase/util/poweroftwo.h

@@ -0,0 +1,42 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2022 Jon Beniston, M7RCE                                        //
+//                                                                               //
+// This program is free software; you can redistribute it and/or modify          //
+// it under the terms of the GNU General Public License as published by          //
+// the Free Software Foundation as version 3 of the License, or                  //
+// (at your option) any later version.                                           //
+//                                                                               //
+// This program is distributed in the hope that it will be useful,               //
+// but WITHOUT ANY WARRANTY; without even the implied warranty of                //
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                  //
+// GNU General Public License V3 for more details.                               //
+//                                                                               //
+// You should have received a copy of the GNU General Public License             //
+// along with this program. If not, see <http://www.gnu.org/licenses/>.          //
+///////////////////////////////////////////////////////////////////////////////////
+
+#ifndef INCLUDE_POWEROFTWO_H
+#define INCLUDE_POWEROFTWO_H
+
+#include <cstdint>
+
+// Is x a power of two
+// From: https://stackoverflow.com/questions/600293/how-to-check-if-a-number-is-a-power-of-2
+static bool isPowerOfTwo(uint32_t x)
+{
+    return (x & (x - 1)) == 0;
+}
+
+// Calculate next power of 2 lower than x
+// From: https://stackoverflow.com/questions/2679815/previous-power-of-2
+static uint32_t lowerPowerOfTwo(uint32_t x)
+{
+    x = x | (x >> 1);
+    x = x | (x >> 2);
+    x = x | (x >> 4);
+    x = x | (x >> 8);
+    x = x | (x >> 16);
+    return x - (x >> 1);
+}
+
+#endif /* INCLUDE_POWEROFTWO_H */