1 files changed, 62 insertions, 0 deletions
diff --git a/prism/src/unpack.rs b/prism/src/unpack.rs
new file mode 100644
index 0000000..03e0018
--- /dev/null
+++ b/prism/src/unpack.rs
@@ -0,0 +1,62 @@
+const TEN_MASK: u64 = 1023; // ten bits
+
+pub fn tenbit(packd: &[u8], count: usize, upack: &mut [u16]) {
+	let required_len_packd = (count as f32 * (10.0 / 8.0)).ceil() as usize;
+
+	println!(
+		"requires {required_len_packd} bytes | {} groups of 5",
+		count / 4
+	);
+
+	if count > upack.len() {
+		panic!(
+			"expected output buffer to be {count} bytes, got {} bytes",
+			upack.len()
+		)
+	}
+
+	if required_len_packd > packd.len() {
+		panic!(
+			"expected input to be at least {required_len_packd} bytes, it was {}",
+			packd.len()
+		)
+	}
+
+	let mut packd = packd[..required_len_packd].to_vec();
+	packd.reverse();
+	let chunker = packd.chunks_exact(5);
+	let remain = chunker.remainder();
+
+	for (idx, chnk) in chunker.enumerate() {
+		let long = u64::from_be_bytes([
+			0x00, 0x00, 0x00, chnk[0], chnk[1], chnk[2], chnk[3], chnk[4],
+		]);
+
+		let b4 = long & TEN_MASK;
+		let b3 = (long >> 10) & TEN_MASK;
+		let b2 = (long >> 20) & TEN_MASK;
+		let b1 = (long >> 30) & TEN_MASK;
+
+		let idx = idx * 4;
+		upack[idx] = b1 as u16;
+		upack[idx + 1] = b2 as u16;
+		upack[idx + 2] = b3 as u16;
+		upack[idx + 3] = b4 as u16;
+	}
+
+	if remain.len() > 0 {
+		let mut long_bytes = [0x00; 8];
+
+		for (idx, byte) in remain.iter().enumerate() {
+			long_bytes[idx] = *byte;
+		}
+
+		let long = u64::from_le_bytes(long_bytes);
+
+		let count_remain = count % 4;
+		let start = count - count_remain;
+		for idx in 0..count_remain {
+			upack[start + idx] = ((long >> (10 * idx)) & TEN_MASK) as u16;
+		}
+	}
+}