Collect the 16-bit signed range sample clipping routines scattered about, which can be optimized on armv6 and create firmware/export/dsp-util.h (for lack of better place right now).

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@31142 a1c6a512-1295-4272-9138-f99709370657

firmware/export/dsp-util.h

@@ -0,0 +1,51 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2011 by Michael Sevakis
+ *
+ * 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 software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#ifndef DSP_HELPER_H
+#define DSP_HELPER_H
+
+/** Clip sample to signed 16 bit range **/
+
+#ifdef CPU_ARM
+#if ARM_ARCH >= 6
+static FORCE_INLINE int32_t clip_sample_16(int32_t sample)
+{
+    int32_t out;
+	asm ("ssat %0, #16, %1"
+        : "=r" (out) : "r"(sample));
+    return out;
+}
+#define CLIP_SAMPLE_16_DEFINED
+#endif /* ARM_ARCH */
+#endif /* CPU_ARM */
+
+#ifndef CLIP_SAMPLE_16_DEFINED
+/* Generic implementation */
+static FORCE_INLINE int32_t clip_sample_16(int32_t sample)
+{
+    if ((int16_t)sample != sample)
+        sample = 0x7fff ^ (sample >> 31);
+    return sample;
+}
+#endif /* CLIP_SAMPLE_16_DEFINED */
+
+#undef CLIP_SAMPLE_16_DEFINED
+
+#endif /* DSP_HELPER_H */