Most people don’t! Operating systems do

Embedded systems programming Flags, etc.

People short on memory resources do, Can pack boolean values into an int Examples: std::bitset

You do! Since Program 3 requires bitwise

operations

Bitwise-OR (|) Bitwise-AND (&) Bitwise-XOR (^) (“exclusive-or”) Bitwise-NOT (~) Shift-left (<<) Shift-right (>>) Only work on integers

Any size (char, short, int, long) Unsigned integers should be used▪ To avoid sign extension with >> and integral

promotion

Test, set, reset, or flip (toggle) bits

Extract a subset of bits as a number

ANDing a bit with a 1 reads it (b & 1 == b) ORing a bit with 1 sets it to 1 (b | 1 == 1) ANDing a bit with 0 resets it (b & 0 == 0) XORing a bit with 1 flips it (b ^ 1 == ~b)

ORing a bit with 0 is a nop (b | 0 == b) ANDing a bit with 1 is a nop (b & 1 == b) XORing a bit with 0 is a nop (b ^ 0 == b)

First form a one-mask Place 1 in the desired bit position (n),

zeroes elsewhere: unsigned mask = 1u << n Note: bit-0 is on the far right (1’s place)

Then AND it with the number x & mask

The result is non-zero iff the bit is 1 To convert the result to 1 or 0: !!(x & mask)

OR the 1-mask into the number x |= mask

To set all bits: x = -1, or x = ~0u (preferred)

Mask to set the lower n bits: mask = (1u << n) – 1 (preferred), or mask = ~0u >> (NBITS – n)▪ NBITS is number bits in an int (= sizeof(int) *

CHAR_BIT) Mask to set bits m through n (inclusive, m

< n): mask = (1u << (n-m+1) – 1) << m

Form a 0-mask 0 in the bit position, 1’s elsewhere By flipping the 1-mask: unsigned mask = ~(1u << n)

Then AND into the number: x &= mask

Flip the corresponding masks for setting bits forming 0-masks

Then AND the mask into the number

If the desired value is 0, reset the bitOtherwise set itNo short-cut!

Form the appropriate 1-maskx ^= mask

Form the 1-mask to extract the bits By ANDing

Shift right the appropriate number of positions so the right-most bit of interest is in the

1’s placeExample: bitops.cpp

Extracts components of an IEEE float