1 files changed, 101 insertions, 0 deletions
diff --git a/setedit/mp3/libamp/position.c b/setedit/mp3/libamp/position.c
new file mode 100644
index 0000000..005f430
--- /dev/null
+++ b/setedit/mp3/libamp/position.c
@@ -0,0 +1,101 @@
+/* this file is a part of amp software, (C) tomislav uzelac 1996,1997
+*/
+/* position.c 	ffwd/rew within a stream
+ *
+ * Creted by: Tomislav Uzelac, May 10 1997
+ */
+#include "amp.h"
+#include "audio.h"
+#include "getbits.h"
+
+#define POSITION
+#include "position.h"
+
+/* Returns the number of frames actually skipped, -1 on error.
+ *
+ * Values in header are not changed if retval!=nframes.
+ * This is not necessary because gethdr() doesn't clobber
+ * the contents of header, but I don't want to rely on that. 
+ */
+int ffwd(struct AUDIO_HEADER *header, int nframes)
+{
+int cnt=0,g;
+int hsize,bitrate,fs,mean_frame_size;
+struct AUDIO_HEADER tmp;
+	memcpy(&tmp,header,sizeof(tmp));
+
+	while (cnt < nframes) {
+	        if (tmp.ID)
+        	        if (tmp.mode==3) hsize=21;
+                	else hsize=36;
+        	else
+                	if (tmp.mode==3) hsize=13;
+               	 	else  hsize=21;
+                if (tmp.protection_bit==0) hsize+=2;
+		if ((g=dummy_getinfo(hsize)))  /* dummy_getinfo: reads hsize-4 bytes */
+			switch (g) {
+                        case GETHDR_EOF: return cnt;
+			case GETHDR_ERR:
+			default:	return -1;
+                        }
+
+	        bitrate=t_bitrate[tmp.ID][3-tmp.layer][tmp.bitrate_index];
+        	fs=t_sampling_frequency[tmp.ID][tmp.sampling_frequency];		
+	        if (tmp.ID) mean_frame_size=144000*bitrate/fs;
+	        else mean_frame_size=72000*bitrate/fs;
+		fillbfr(mean_frame_size + tmp.padding_bit - hsize);
+
+		if ((g=gethdr(&tmp))) 
+			switch (g) {
+			case GETHDR_EOF: return cnt;
+			case GETHDR_ERR:
+			default:	return -1;
+			}
+		cnt++;
+	}	
+
+	memcpy(header,&tmp,sizeof(tmp));		
+	return cnt;
+}
+
+/* Mostly the same as ffwd. Some streams might be 'tough', i.e.
+ * the ones switching bitrates.
+ */
+int rew(struct AUDIO_HEADER *header, int nframes)
+{
+int cnt=0;
+int bitrate,fs,mean_frame_size;
+struct AUDIO_HEADER tmp;
+	memcpy(&tmp,header,sizeof(tmp));
+
+	while (cnt < nframes) {
+		/* ffwd/rew functions are to be called right after the header has been parsed
+		 * so we have to go back one frame + 4 bytes + 1 byte (in case padding was used).
+		 */
+	        bitrate=t_bitrate[tmp.ID][3-tmp.layer][tmp.bitrate_index];
+        	fs=t_sampling_frequency[tmp.ID][tmp.sampling_frequency];		
+	        if (tmp.ID) mean_frame_size=144000*bitrate/fs;
+	        else mean_frame_size=72000*bitrate/fs;
+
+		if (rewind_stream(mean_frame_size) !=0) {
+			memcpy(header,&tmp,sizeof(tmp));
+			return cnt;
+		}
+		if ((gethdr(&tmp))) return -1; 
+		cnt++;
+	}
+	/* We have to make sure that the bit reservoir contains enough data.
+	 * Hopefully, layer3_frame will take care of that.
+	 */
+	f_bdirty=TRUE;
+	bclean_bytes=0;
+
+	memcpy(header,&tmp,sizeof(tmp));		
+	return cnt;
+}
+
+/* TODO: after the gethdr function is enhanced with the counter to count
+ * the number of bytes to search for the next syncword, make the call to
+ * gethdr() from rew() have that counter something like (frame_size-1) so
+ * that we don't go back again and again to the same header. (not very important)
+ */