Direct Stream Digital (DSD) decoder

Signed-off-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

1 files changed, 95 insertions, 0 deletions

diff --git a/libavcodec/dsd_tablegen.h b/libavcodec/dsd_tablegen.h
new file mode 100644
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+++ b/libavcodec/dsd_tablegen.h
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+/*
+ * Header file for hardcoded DSD tables
+ * based on BSD licensed dsd2pcm by Sebastian Gesemann
+ * Copyright (c) 2009, 2011 Sebastian Gesemann. All rights reserved.
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVCODEC_DSD_TABLEGEN_H
+#define AVCODEC_DSD_TABLEGEN_H
+
+#include <stdint.h>
+#include "libavutil/attributes.h"
+
+#define HTAPS   48                /** number of FIR constants */
+#define CTABLES ((HTAPS + 7) / 8) /** number of "8 MACs" lookup tables */
+
+#if CONFIG_HARDCODED_TABLES
+#define dsd_ctables_tableinit()
+#include "libavcodec/dsd_tables.h"
+#else
+#include "libavutil/common.h"
+
+/*
+ * Properties of this 96-tap lowpass filter when applied on a signal
+ * with sampling rate of 44100*64 Hz:
+ *
+ * () has a delay of 17 microseconds.
+ *
+ * () flat response up to 48 kHz
+ *
+ * () if you downsample afterwards by a factor of 8, the
+ *    spectrum below 70 kHz is practically alias-free.
+ *
+ * () stopband rejection is about 160 dB
+ *
+ * The coefficient tables ("ctables") take only 6 Kibi Bytes and
+ * should fit into a modern processor's fast cache.
+ */
+
+/**
+ * The 2nd half (48 coeffs) of a 96-tap symmetric lowpass filter
+ */
+static const double htaps[HTAPS] = {
+     0.09950731974056658,    0.09562845727714668,    0.08819647126516944,
+     0.07782552527068175,    0.06534876523171299,    0.05172629311427257,
+     0.0379429484910187,     0.02490921351762261,    0.0133774746265897,
+     0.003883043418804416,  -0.003284703416210726,  -0.008080250212687497,
+    -0.01067241812471033,   -0.01139427235000863,   -0.0106813877974587,
+    -0.009007905078766049,  -0.006828859761015335,  -0.004535184322001496,
+    -0.002425035959059578,  -0.0006922187080790708,  0.0005700762133516592,
+     0.001353838005269448,   0.001713709169690937,   0.001742046839472948,
+     0.001545601648013235,   0.001226696225277855,   0.0008704322683580222,
+     0.0005381636200535649,  0.000266446345425276,   7.002968738383528e-05,
+    -5.279407053811266e-05, -0.0001140625650874684, -0.0001304796361231895,
+    -0.0001189970287491285, -9.396247155265073e-05, -6.577634378272832e-05,
+    -4.07492895872535e-05,  -2.17407957554587e-05,  -9.163058931391722e-06,
+    -2.017460145032201e-06,  1.249721855219005e-06,  2.166655190537392e-06,
+     1.930520892991082e-06,  1.319400334374195e-06,  7.410039764949091e-07,
+     3.423230509967409e-07,  1.244182214744588e-07,  3.130441005359396e-08
+};
+
+static float ctables[CTABLES][256];
+
+static av_cold void dsd_ctables_tableinit(void)
+{
+    int t, e, m, k;
+    double acc;
+    for (t = 0; t < CTABLES; ++t) {
+        k = FFMIN(HTAPS - t * 8, 8);
+        for (e = 0; e < 256; ++e) {
+            acc = 0.0;
+            for (m = 0; m < k; ++m)
+                acc += (((e >> (7 - m)) & 1) * 2 - 1) * htaps[t * 8 + m];
+            ctables[CTABLES - 1 - t][e] = (float)acc;
+        }
+    }
+}
+#endif /* CONFIG_HARDCODED_TABLES */
+
+#endif /* AVCODEC_DSD_TABLEGEN_H */