1Bitwise Operators11/19/20072Opening Discussion■Let's look at solutions to the interclass problem.■Do you have any questions about the assignment?3Motivating Bitwise Operators■There are a number of situations in which being able to play directly with the bits in numbers can be helpful.■Consider an application where you must keep a large number of boolean values.■Another is when you need to build a single number from several other values, often booleans.Packing booleansPacking RGB valuesPassing multiple flags to a function4&, |, and ^■There are three binary bitwise operators. That is, three operators that work on the individual bits in numbers and take two operands.■& is bitwise and. A bit is only turned on in the result if the bit in that position in both operands is on.■| is bitwise or. A bit will be on in the result if either of the bits in that position in the operands are on.■^ is bitwise xor (exculsive or). A bit in the result will be on if it is on in only one of the two operands, but not both.5~■This is the bitwise not operator.■It is unary.■Applied to an integer value it flips the states of all the bits in that value.■Note that ~0 gives you a number with all the bits on, regardless of the number of bits.6>> and <<■These are bit shifting operators.■They are binary and move the bits in the first argument either up or down by the number of places specified in the second argument.■The upshift, <<, basically works like multiplying by a power of two while downshift, >>, is basically dividing by a power of two.7Combining Operators/Masks■Combining the different bitwise operators allows us to specifically check or set any combination of bits in a number that we want to.■This is the real power of bitwise operators.■These are often combined with hex literals for masking off different parts of numbers.■^ allows you to swap ints without a temporary. Don't bother doing this. It's just a fun trick to know.8Assignment Operators■All the binary bitwise operators can be used in an assignment form by putting them before = in an assignment.■So for integers, a*=2 is the same as a<<=1.■I find that I use &= and |= fairly often when going through loops that build values through bitwise operations.9Minute Essay■For the fun class would you rather do cover ASCII based graphics or X11 based graphics?■Interclass Problem – Do problem 46 on page
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