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libmc-common/src/commonMain/kotlin/cn/rtast/libmc/primitives/BitSet.kt

@@ -33,3 +33,32 @@ public fun BitSet.getBit(bitIndex: Int): Boolean {
     val bitOffset = bitIndex and 63
     return (this[longIndex] and (1L shl bitOffset)) != 0L
 }
+
+public class FixedBitSet20(initialBits: Int = 0) {
+    private var bits: Int = initialBits and 0xFFFFF
+
+    public operator fun get(index: Int): Boolean {
+        require(index in 0..19) { "Index out of range [0, 19]" }
+        return (bits and (1 shl index)) != 0
+    }
+
+    public operator fun set(index: Int, value: Boolean) {
+        require(index in 0..19) { "Index out of range [0, 19]" }
+        bits = if (value) {
+            bits or (1 shl index)
+        } else {
+            bits and (1 shl index).inv()
+        }
+    }
+
+    public fun toByteArray(): ByteArray {
+        val result = ByteArray(3)
+        result[0] = (bits and 0xFF).toByte()
+        result[1] = ((bits shr 8) and 0xFF).toByte()
+        result[2] = ((bits shr 16) and 0x0F).toByte()
+        return result
+    }
+}
+
+public fun createFixedBitSet20(initialBits: Int = 0): FixedBitSet20 =
+    FixedBitSet20(initialBits)