diff --git a/src/io/nayuki/fastqrcodegen/BitBuffer.java b/src/io/nayuki/fastqrcodegen/BitBuffer.java
new file mode 100644
index 0000000..c612029
--- /dev/null
+++ b/src/io/nayuki/fastqrcodegen/BitBuffer.java
@@ -0,0 +1,56 @@
+package io.nayuki.fastqrcodegen;
+
+import java.util.Arrays;
+
+
+final class BitBuffer {
+	
+	/*---- Fields ----*/
+	
+	private int[] data;
+	
+	private int bitLength;
+	
+	
+	
+	/*---- Constructors ----*/
+	
+	public BitBuffer() {
+		data = new int[64];
+		bitLength = 0;
+	}
+	
+	
+	
+	/*---- Methods ----*/
+	
+	public int getBit(int index) {
+		if (index < 0 || index >= bitLength)
+			throw new IndexOutOfBoundsException();
+		return (data[index >>> 5] >>> ~index) & 1;
+	}
+	
+	
+	public void appendBits(int val, int len) {
+		if (len < 0 || len > 31 || val >>> len != 0)
+			throw new IllegalArgumentException("Value out of range");
+		
+		if (bitLength + len + 1 > data.length << 5)
+			data = Arrays.copyOf(data, data.length * 2);
+		assert bitLength + len <= data.length << 5;
+		
+		int remain = 32 - (bitLength & 0x1F);
+		assert 1 <= remain && remain <= 32;
+		if (remain < len) {
+			data[bitLength >>> 5] |= val >>> (len - remain);
+			bitLength += remain;
+			assert (bitLength & 0x1F) == 0;
+			len -= remain;
+			val &= (1 << len) - 1;
+			remain = 32;
+		}
+		data[bitLength >>> 5] |= val << (remain - len);
+		bitLength += len;
+	}
+	
+}