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bits.py

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def hamming_distance(x, y):

difference = x ^ y

count = 0

while difference:

# this removes ones from right to left (least to most significant)

difference &= difference - 1

count += 1

return count

# Wegner method

def hamming_weight(x):

if x < 0:

return None

count = 0

while x:

x &= x - 1

count += 1

return count

def pop_count(i):

i -= ((i >> 1) & 0x55555555)

i = (i & 0x33333333) + ((i >> 2) & 0x33333333)

return (((i + (i >> 4) & 0xF0F0F0F) * 0x1010101) & 0xffffffff) >> 24

def is_bit_set(x, pos):

return (x & (1 << pos)) != 0

def is_even(x):

return x & 1 == 0

def is_power_of_2(x):

return (x & x - 1) == 0

# Returns the n bits in bitfield starting at position pos

def get_bits(x, pos, n):

return (x >> (pos + 1 - n)) & ~(~0 << n)

def set_bit(x, position):

return x | (1 << position)

def clear_bit(x, position):

return x & ~(1 << position)

def toggle_bit(x, position):

return x ^ (1 << position)

def rotate_left(x, n):

print(bin(-n & 31))

return (x << n) | (x >> (-n & 31)) # assumes a 32 bit word size

def add(a, b):

while a:

c = b & a

b ^= a

c <<= 1

a = c

return b

def get_sign(x):

return -(x < 0)

# has odd number of bits

def has_parity(x):

parity = False

while x:

parity = not parity

x &= (x - 1)

return parity

def has_parity_parallel(x):

x ^= x >> 16

x ^= x >> 8

x ^= x >> 4

x &= 0xf

return (0x6996 >> x) & 1

def next_power_of_2(x):

x -= 1

x |= x >> 1

x |= x >> 2

x |= x >> 4

x |= x >> 8

x |= x >> 16

x += 1

return x

#

# def modulo(x, y):

# return x & ((1 << y) - 1)

# high_bit_mask will be all 1s if negative or all 0 if positive

# for negative will NOT(x) - (-1) = NOT(x) + 1, which is two's complement conversion from negative to positive

def myabs(x):

high_bit_mask = x >> 31

return (x ^ high_bit_mask) - high_bit_mask

def swap_ints(a, b):

a ^= b

b ^= a

a ^= b

return [a, b]

def main():

for x in range(0, 20):

print(x, bin(x), hex(x))

print("Hamming distance: 1010111100 and 1001010101: ", hamming_distance(0b1010111100, 0b1001010101))

print("Bit 0: 1011 1100 set?", is_bit_set(0b10111100, 0))

print("Bit 1: 1011 1100 set?", is_bit_set(0b10111100, 1))

print("Bit 2: 1011 1100 set?", is_bit_set(0b10111100, 2))

print("Bit 3: 1011 1100 set?", is_bit_set(0b10111100, 3))

print("Bit 4: 1011 1100 set?", is_bit_set(0b10111100, 4))

print("Bit 5: 1011 1100 set?", is_bit_set(0b10111100, 5))

print("Bit 6: 1011 1100 set?", is_bit_set(0b10111100, 6))

print("Bit 7: 1011 1100 set?", is_bit_set(0b10111100, 7))

print("Hamming weight: 1010111100:", hamming_weight(0b1010111100))

print("Hamming weight: 1001000001:", hamming_weight(0b1001000001))

print("Hamming weight: 0001000000:", hamming_weight(0b0001000000))

print("Hamming weight: 0000000000:", hamming_weight(0b0000000000))

print("Hamming weight: 11111111:", hamming_weight(0b11111111))

print("PopCount: " + str(bin(1231424)) + ":", pop_count(1231424))

print("PopCount: " + str(bin(123)) + ":", pop_count(123))

print("PopCount: " + str(bin(8568)) + ":", pop_count(8568))

print("PopCount: " + str(bin(1)) + ":", pop_count(1))

print("PopCount: " + str(bin(-1)) + ":", pop_count(-1))

print("PopCount: " + str(bin(4)) + ":", pop_count(4))

print("PopCount: " + str(bin(903523125)) + ":", pop_count(903523125))

for x in range(0, 5):

print(str(x) + " is even?", is_even(x))

for x in range(0, 17):

print(str(x) + " is power of 2?", is_power_of_2(x))

print("Get 3 bits starting at position 5 in 1010111100", bin(get_bits(0b1010111100, 5, 3)))

print("Get 3 bits starting at position 8 in 1010111100", bin(get_bits(0b1010111100, 9, 3)))

print("Set bit 4 to 0: 01010010", bin(clear_bit(0b01010010, 4)))

print("Set bit 0 to 1: 01010010", bin(set_bit(0b01010010, 0)))

print("Toggle bit 1: 01010010", bin(toggle_bit(0b01010010, 1)))

print("Toggle bit 3: 01010010", bin(toggle_bit(0b01010010, 3)))

print("Rotate left 5 positions: 01001000100101011001010010011011:",

bin(rotate_left(0b01001000100101011001010010011011, 5)))

print("3 + 5 = ", add(3, 5))

print("33 + 51 = ", add(33, 51))

print("40 + 90 = ", add(40, 90))

print("45 + 15 = ", add(45, 15))

print("Sign of 45", get_sign(45))

print("Sign of 0", get_sign(0))

print("Sign of -1", get_sign(-1))

print("Sign of -23", get_sign(-23))

for x in range(0, 12):

print("has parity: " + str(x), has_parity(x), bin(x))

for x in range(0, 7):

print("has parity (parallel): " + str(x), has_parity_parallel(x), bin(x))

print("Next power of 2 after 3", next_power_of_2(3))

print("Next power of 2 after 4", next_power_of_2(4))

print("Next power of 2 after 7", next_power_of_2(7))

print("Next power of 2 after 12", next_power_of_2(12))

print("Next power of 2 after 45", next_power_of_2(45))

# print("3 mod 5", modulo(3, 5))

# print("4 mod 2", modulo(4, 2))

# print("5 mod 2", modulo(5, 2))

# print("10 mod 3", modulo(10, 3))

# print("10 mod 4", modulo(10, 4))

# print("10 mod 5", modulo(10, 5))

print("abs -1", myabs(-1))

print("abs -134", myabs(-134))

print("abs 99", myabs(99))

print("abs 0", myabs(0))

print("abs 16", myabs(16))

print("swap 1, 3", swap_ints(1, 3))

print("swap 213, 14", swap_ints(213, 14))

print("swap 872, 992", swap_ints(872, 992))

if __name__ == "__main__":

main()