Add more conversion utility functions.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

sapling_utils.py

@@ -10,26 +10,58 @@ def i2lebsp(l, x):
 def leos2ip(S):
     return int.from_bytes(S, byteorder='little')
 
+def beos2ip(S):
+    return int.from_bytes(S, byteorder='big')
+
 # This should be equivalent to LEBS2OSP(I2LEBSP(l, x))
 def i2leosp(l, x):
     return x.to_bytes(cldiv(l, 8), byteorder='little')
 
-def ledna(bits):
+# This should be equivalent to BEBS2OSP(I2BEBSP(l, x))
+def i2beosp(l, x):
+    return x.to_bytes(cldiv(l, 8), byteorder='big')
+
+def bebs2ip(bits):
     ret = 0
-    for b in bits[::-1]:
+    for b in bits:
         ret = ret * 2
         if b:
             ret += 1
     return ret
 
+def lebs2ip(bits):
+    return bebs2ip(bits[::-1])
+
+def i2bebsp(m, x):
+    assert 0 <= x and x < (1 << m)
+    return [(x >> (m-1-i)) & 1 for i in range(m)]
+
 def lebs2osp(bits):
     l = len(bits)
     bits = bits + [0] * (8 * cldiv(l, 8) - l)
-    return bytes([ledna(bits[i:i + 8]) for i in range(0, len(bits), 8)])
+    return bytes([lebs2ip(bits[i:i + 8]) for i in range(0, len(bits), 8)])
 
 def leos2bsp(buf):
     return sum([[(c >> i) & 1 for i in range(8)] for c in buf], [])
 
+def bebs2osp(bits, m=None):
+    l = len(bits)
+    bits = [0] * (8 * cldiv(l, 8) - l) + bits
+    return bytes([bebs2ip(bits[i:i + 8]) for i in range(0, len(bits), 8)])
+
+def beos2bsp(buf):
+    return sum([[(c >> (7-i)) & 1 for i in range(8)] for c in buf], [])
 
 assert i2leosp(5, 7) == lebs2osp(i2lebsp(5, 7))
 assert i2leosp(32, 1234567890) == lebs2osp(i2lebsp(32, 1234567890))
+
+assert i2beosp(5, 7) == bebs2osp(i2bebsp(5, 7))
+assert i2beosp(32, 1234567890) == bebs2osp(i2bebsp(32, 1234567890))
+
+assert bebs2ip(i2bebsp(5, 7)) == 7
+try:
+    i2bebsp(3, 12)
+except AssertionError:
+    pass
+else:
+    raise AssertionError("invalid input not caught by i2bebsp")