'''
Write a program that takes a 64bit unsigned integer and returns the 64bit usigned integer consisting of the bits
of the input in reverse order.
'''
#brute force with swap bit function
def reverse_bits(x):
LENGTH = 64
for i in range(LENGTH//2):
x = swap_bit(x, LENGTH-i, i)
return x
#Use a lookup table, 2^16 = 60k combination
def reverse_bits(x):
MASK_SIZE = 16
BIT_MASK = 0XFFFF
return (PRECOMPUTED_REVERSE[x & BIT_MASK] << (3 * MASK_SIZE) |
PRECOMPUTED_REVERSE[(x >> MASK_SIZE) & BIT_MASK] << (2 * MASK_SIZE) |
PRECOMPUTED_REVERSE[(x >> (2 * MASK_SIZE)) & BIT_MASK] << MASK_SIZE |
PRECOMPUTED_REVERSE[(x >> (3 * MASK_SIZE)) & BIT_MASK])
