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[bup.git] / lib / bup / vint.py

diff --git a/lib/bup/vint.py b/lib/bup/vint.py
new file mode 100644 (file)
index 0000000..31e2dfa
--- /dev/null
+++ b/lib/bup/vint.py
@@ -0,0 +1,83 @@
+"""Binary encodings for bup."""
+
+# Copyright (C) 2010 Rob Browning
+#
+# This code is covered under the terms of the GNU Library General
+# Public License as described in the bup LICENSE file.
+
+from cStringIO import StringIO
+
+# Variable length integers are encoded as vints -- see jakarta lucene.
+
+def write_vuint(port, x):
+    if x < 0:
+        raise Exception("vuints must not be negative")
+    elif x == 0:
+        port.write('\0')
+    else:
+        while x:
+            seven_bits = x & 0x7f
+            x >>= 7
+            if x:
+                port.write(chr(0x80 | seven_bits))
+            else:
+                port.write(chr(seven_bits))
+
+
+def read_vuint(port):
+    c = port.read(1)
+    if c == '':
+        raise EOFError('encountered EOF while reading vuint');
+    result = 0
+    offset = 0
+    while c:
+        b = ord(c)
+        if b & 0x80:
+            result |= ((b & 0x7f) << offset)
+            offset += 7
+            c = port.read(1)
+        else:
+            result |= (b << offset)
+            break
+    return result
+
+
+def write_bvec(port, x):
+    write_vuint(port, len(x))
+    port.write(x)
+
+
+def read_bvec(port):
+    n = read_vuint(port)
+    return port.read(n)
+
+
+def skip_bvec(port):
+    port.read(read_vuint(port))
+
+
+def pack(types, *args):
+    if len(types) != len(args):
+        raise Exception('number of arguments does not match format string')
+    port = StringIO()
+    for (type, value) in zip(types, args):
+        if type == 'V':
+            write_vuint(port, value)
+        elif type == 's':
+            write_bvec(port, value)
+        else:
+            raise Exception('unknown xpack format string item "' + type + '"')
+    return port.getvalue()
+
+
+def unpack(types, data):
+    result = []
+    port = StringIO(data)
+    for type in types:
+        if type == 'V':
+            result.append(read_vuint(port))
+        elif type == 's':
+            result.append(read_bvec(port))
+        else:
+            raise Exception('unknown xunpack format string item "' + type + '"')
+    return result