dsd2pcm: move the bit reversing code to a generic library

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

2 files changed, 66 insertions, 0 deletions

diff --git a/src/util/bit_reverse.c b/src/util/bit_reverse.c
new file mode 100644
index 00000000..ba8a23ef
--- /dev/null
+++ b/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)
+};
diff --git a/src/util/bit_reverse.h b/src/util/bit_reverse.h
new file mode 100644
index 00000000..e44693b1
--- /dev/null
+++ b/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