1 files changed, 32 insertions, 0 deletions
diff --git a/filt/f_5th.c b/filt/f_5th.c
new file mode 100644
index 0000000..811fb18
--- /dev/null
+++ b/filt/f_5th.c
@@ -0,0 +1,32 @@
+#include "filt.h"
+
+void f_5th(int16_t *data, int length, int16_t *hist)
+/* for half of interleaved data */
+{
+	int i;
+	int16_t a, b, c, d, e, f;
+	a = hist[1];
+	b = hist[2];
+	c = hist[3];
+	d = hist[4];
+	e = hist[5];
+	f = data[0];
+	/* a downsample should improve resolution, so don't fully shift */
+	data[0] = (a + (b+e)*5 + (c+d)*10 + f) >> 4;
+	for (i=4; i<length; i+=4) {
+		a = c;
+		b = d;
+		c = e;
+		d = f;
+		e = data[i-2];
+		f = data[i];
+		data[i/2] = (a + (b+e)*5 + (c+d)*10 + f) >> 4;
+	}
+	/* archive */
+	hist[0] = a;
+	hist[1] = b;
+	hist[2] = c;
+	hist[3] = d;
+	hist[4] = e;
+	hist[5] = f;
+}
+\ No newline at end of file