dsd2pcm: move the bit reversing code to a generic library

Instead of doing run-time initialisation, use a constant lookup table.

Makefile.am

@@ -227,6 +227,7 @@ src_mpd_SOURCES = \
 	$(MIXER_API_SRC) \
 	src/util/list.h \
 	src/util/list_sort.c src/util/list_sort.h \
+	src/util/bit_reverse.c src/util/bit_reverse.h \
 	src/glib_socket.h \
 	src/notify.c \
 	src/audio_config.c src/audio_config.h \
@@ -1174,6 +1175,7 @@ test_run_normalize_LDADD = \
 	$(GLIB_LIBS)
 
 test_run_convert_SOURCES = test/run_convert.c \
+	src/util/bit_reverse.c \
 	src/dsd2pcm/dsd2pcm.c \
 	src/fifo_buffer.c \
 	src/audio_format.c \
@@ -1272,6 +1274,7 @@ if HAVE_CXX
 noinst_PROGRAMS += src/dsd2pcm/dsd2pcm
 
 src_dsd2pcm_dsd2pcm_SOURCES = \
+	src/util/bit_reverse.c \
 	src/dsd2pcm/dsd2pcm.c src/dsd2pcm/dsd2pcm.h \
 	src/dsd2pcm/noiseshape.c src/dsd2pcm/noiseshape.h \
 	src/dsd2pcm/main.cpp

src/dsd2pcm/dsd2pcm.c

@@ -1,3 +1,5 @@
+#include "util/bit_reverse.h"
+
 #include <stdlib.h>
 #include <string.h>
 
@@ -84,7 +86,6 @@ static const double htaps[HTAPS] = {
 };
 
 static float ctables[CTABLES][256];
-static unsigned char bitreverse[256];
 static int precalculated = 0;
 
 static void precalc(void)
@@ -92,11 +93,6 @@ static void precalc(void)
 	int t, e, m, k;
 	double acc;
 	if (precalculated) return;
-	for (t=0, e=0; t<256; ++t) {
-		bitreverse[t] = e;
-		for (m=128; m && !((e^=m)&m); m>>=1)
-			;
-	}
 	for (t=0; t<CTABLES; ++t) {
 		k = HTAPS - t*8;
 		if (k>8) k=8;
@@ -170,10 +166,10 @@ extern void dsd2pcm_translate(
 	lsbf = lsbf ? 1 : 0;
 	while (samples-- > 0) {
 		bite1 = *src & 0xFFu;
-		if (lsbf) bite1 = bitreverse[bite1];
+		if (lsbf) bite1 = bit_reverse(bite1);
 		ptr->fifo[ffp] = bite1; src += src_stride;
 		p = ptr->fifo + ((ffp-CTABLES) & FIFOMASK);
-		*p = bitreverse[*p & 0xFF];
+		*p = bit_reverse(*p);
 		acc = 0;
 		for (i=0; i<CTABLES; ++i) {
 			bite1 = ptr->fifo[(ffp              -i) & FIFOMASK] & 0xFF;

src/util/bit_reverse.c

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2003-2012 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * 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; either version 2 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 for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "bit_reverse.h"
+
+/**
+ * @see http://graphics.stanford.edu/~seander/bithacks.html#BitReverseTable
+ */
+const uint8_t bit_reverse_table[256] =
+{
+#define R2(n)     n,     n + 2*64,     n + 1*64,     n + 3*64
+#define R4(n) R2(n), R2(n + 2*16), R2(n + 1*16), R2(n + 3*16)
+#define R6(n) R4(n), R4(n + 2*4 ), R4(n + 1*4 ), R4(n + 3*4 )
+    R6(0), R6(2), R6(1), R6(3)
+};

src/util/bit_reverse.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2003-2012 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * 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; either version 2 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 for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_BIT_REVERSE_H
+#define MPD_BIT_REVERSE_H
+
+#include <glib.h>
+#include <stdint.h>
+
+extern const uint8_t bit_reverse_table[256];
+
+G_GNUC_CONST
+static inline uint8_t
+bit_reverse(uint8_t x)
+{
+	return bit_reverse_table[x];
+}
+
+#endif