koddecoder: added koencode

1 files changed, 22 insertions, 0 deletions

diff --git a/koddecoder.py b/koddecoder.py
index b98ffe6..6489a88 100644
--- a/koddecoder.py
+++ b/koddecoder.py
@@ -25,8 +25,30 @@ KOD = [
     0xfc, 0x84, 0xe5, 0xf9, 0x14, 0x19, 0xdf, 0x6e, 0x23, 0xc4, 0x66, 0xeb,
     0xcc, 0x22, 0x1c, 0x5c,
 ]
+INV = [0] *256
+def calc_inverse():
+    global INV
+    for i, x in enumerate(KOD):
+        INV[x] = i
+
 def kodecode(o, data):
+    """
+    decode : shift, a[0]..a[n-1] -> b[0]..b[n-1]
+
+        b[i] = KOD[a[i]]- (i+shift)
+    """
     global KOD
     return bytes((KOD[b] - i - o)%256 for i, b in enumerate(data))
 
+def koencode(o, data):
+    """
+    encode : shift, b[0]..b[n-1] -> a[0]..a[n-1]
+
+        a[i] = INV[b[i]+ (i+shift)]
+
+    """
+    global INV
+    return bytes(INV[(b + i + o)%256] for i, b in enumerate(data))
+
+calc_inverse()