Merge pull request keon#58 from ofek/bytes-int-conversion

add bytes <-> int conversion

Author: ankit167

README.md

@@ -38,6 +38,7 @@ Minimal and clean example implementations of data structures and algorithms in P
     - [shortest_distance_from_all_buildings](bfs/shortest_distance_from_all_buildings.py)
     - [word_ladder](bfs/word_ladder.py)
 - [bit](bit)
+    - [bytes_int_conversion](bit/bytes_int_conversion.py)
     - [count_ones](bit/count_ones.py)
     - [power_of_two](bit/power_of_two.py)
     - [reverse_bits](bit/reverse_bits.py)

bit/bytes_int_conversion.py

@@ -0,0 +1,35 @@
+from collections import deque
+
+
+def int_to_bytes_big_endian(num):
+    bytestr = deque()
+    while num > 0:
+        # list.insert(0, ...) is inefficient
+        bytestr.appendleft(num & 0xff)
+        num >>= 8
+    return bytes(bytestr)
+
+
+def int_to_bytes_little_endian(num):
+    bytestr = []
+    while num > 0:
+        bytestr.append(num & 0xff)
+        num >>= 8
+    return bytes(bytestr)
+
+
+def bytes_big_endian_to_int(bytestr):
+    num = 0
+    for b in bytestr:
+        num <<= 8
+        num += b
+    return num
+
+
+def bytes_little_endian_to_int(bytestr):
+    num = 0
+    e = 0
+    for b in bytestr:
+        num += b << e
+        e += 8
+    return num