Initial commit

ackit/bits.py

@@ -0,0 +1,67 @@
+"""LSB-first bit reader/writer (Vorbis bit packing order)."""
+
+
+class BitReader:
+    def __init__(self, data: bytes, bitpos: int = 0):
+        self.data = data
+        self.pos = bitpos
+
+    def get(self, n: int) -> int:
+        v = 0
+        for i in range(n):
+            byte = self.data[(self.pos >> 3)] if (self.pos >> 3) < len(self.data) else 0
+            v |= ((byte >> (self.pos & 7)) & 1) << i
+            self.pos += 1
+        return v
+
+    def bits_left(self) -> int:
+        return len(self.data) * 8 - self.pos
+
+
+class BitWriter:
+    def __init__(self):
+        self.buf = bytearray()
+        self.pos = 0
+
+    def put(self, n: int, v: int):
+        for i in range(n):
+            if (self.pos >> 3) >= len(self.buf):
+                self.buf.append(0)
+            if (v >> i) & 1:
+                self.buf[self.pos >> 3] |= 1 << (self.pos & 7)
+            self.pos += 1
+
+    def put_bits_from(self, r: BitReader, n: int):
+        """Copy n bits from a reader (fast path in 32-bit chunks)."""
+        while n > 0:
+            k = 32 if n >= 32 else n
+            self.put(k, r.get(k))
+            n -= k
+
+    def bytes(self) -> bytes:
+        return bytes(self.buf)
+
+
+def ilog(v: int) -> int:
+    r = 0
+    while v:
+        r += 1
+        v >>= 1
+    return r
+
+
+def book_maptype1_quantvals(entries: int, dims: int) -> int:
+    bits = ilog(entries)
+    vals = entries >> ((bits - 1) * (dims - 1) // dims)
+    while True:
+        acc = 1
+        acc1 = 1
+        for _ in range(dims):
+            acc *= vals
+            acc1 *= vals + 1
+        if acc <= entries < acc1:
+            return vals
+        if acc > entries:
+            vals -= 1
+        else:
+            vals += 1