Add support for 16 bit 'half float' format PCM.

I'm not 100% sure that the rounding of denormals is correct. As compared to foobar2000,
some samples are off by +1 LSB.  However, since I can't output 24 bit PCM easily with
rockbox, I'm not sure if this is due to a bug or just how rockbox rounds.  In practice
I don't think it matters so I'm just going to commit this for now.

Change-Id: Ic0792fcb172e4369a5512d202121c2b918b36079

1 files changed, 28 insertions, 1 deletions

diff --git a/lib/rbcodec/codecs/libpcm/ieee_float.c b/lib/rbcodec/codecs/libpcm/ieee_float.c
index 639390bcd5..97a7fcecd4 100644
--- a/lib/rbcodec/codecs/libpcm/ieee_float.c
+++ b/lib/rbcodec/codecs/libpcm/ieee_float.c
@@ -38,7 +38,7 @@ static bool set_format(struct pcm_format *format)
         return false;
     }
 
-    if (fmt->bitspersample != 32 && fmt->bitspersample != 64)
+    if (fmt->bitspersample != 16 && fmt->bitspersample != 32 && fmt->bitspersample != 64)
     {
         DEBUGF("CODEC_ERROR: ieee float must be 32 or 64 bitspersample: %d\n",
                              fmt->bitspersample);
@@ -114,6 +114,33 @@ static int decode(const uint8_t *inbuf, size_t inbufsize,
         }
         *outbufsize = inbufsize >> 2;
     }
+    else if (fmt->bitspersample == 16)
+    {
+        for (i = 0; i < inbufsize; i += 2)
+        { 
+            pcm = inbuf[0]|((inbuf[1]&0x03)<<8);
+            exp = ((inbuf[1]&0x7c)>>2)-15;
+            sgn = (inbuf[1] & 0x80)>>7;
+      
+            if(exp == -15)
+                 pcm =0;
+            else
+            {
+                pcm+=1<<10;
+                exp+=2; /*shift by 2 for rockbox fixed format*/
+                if(exp>=0)
+                    pcm <<= (exp); 
+            else
+                    pcm >>= (-exp);             
+
+                if (sgn)
+                    pcm = -pcm;
+                }
+        outbuf[i/2] = pcm;
+        inbuf += 2;
+        }
+        *outbufsize = inbufsize >> 1;
+    }
     else
     {
         for (i = 0; i < inbufsize; i += 8)