adding main file, decode only

diff --git a/base91.py b/base91.py
new file mode 100644 (file)
index 0000000..b91614e
--- /dev/null
+++ b/base91.py
@@ -0,0 +1,38 @@
+import struct
+
+basE91_alphabet = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
+       'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
+       'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
+       'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
+       '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '!', '#', '$',
+       '%', '&', '(', ')', '*', '+', ',', '.', '/', ':', ';', '<', '=',
+       '>', '?', '@', '[', ']', '^', '_', '`', '{', '|', '}', '~', '"']
+
+decode_table = dict((v,k) for k,v in enumerate(basE91_alphabet))
+
+def base91_decode(encoded_str):
+    v = -1
+    b = 0
+    n = 0
+    out = bytearray()
+    for strletter in encoded_str:
+        if not strletter in dectable:
+            continue
+        c = dectable[strletter]
+        if(v < 0):
+            v = c
+        else:
+            v += c*91
+            b |= v << n
+            n += 13 if (v & 8191)>88 else 14
+            while True:
+                out += struct.pack('B', b&255)
+                b >>= 8
+                n -= 8
+                if not n>7:
+                    break
+            v = -1
+    if v+1:
+        out += struct.pack('B', (b | v << n) & 255 )
+    return out
+