Cirrus Logic CS485 Manual de usuario descargar pdf (Pagina 9)

CS485G Spring 2015 9

7. One can use the Boolean operators in C and apply them to any inte-

gral data type: char, short, int, long, long long.

8. Don’t confuse these operators with logical operators &&, ||, and !.

In C, 0 is understood to mean false, and any other value is true. The

logical operators always return either 0 or 1. They use short-circuit

semantics.

11 Shifting operators

1. Left shift: x << y Left-shifts bits in x by y positions; new positions

on the right are ﬁlled with 0. Warning: In C (and Java), if y is equal

to or greater than the number of bits n in the type of x, the shift

distance is y mod n. So shifting a 32-bit integer by 34 bits only shifts

it 34 mod 32 = 2 bits.

2. Right shift: x >> y Right-shifts bits in x by y positions; new posi-

tions on the left are ﬁlled with the sign bit. The same warning ap-

plies.

12 Encoding integers

1. Given n bits, there are 2

possible integers.

2. In unsigned form, these range from 0 (represented as all 0 bits) to

− 1 (represented by all 1 bits).

3. In signed form, these range from −2

n−1

to 2

n−1

− 1.

(a) 0 is represented by all 0 bits.

(b) The most signiﬁcant bit is 0 for positive numbers. The largest

positive number has n − 1 bits set, representing 2

n−1

− 1.

negative number has only that bit set, representing −2

n−1

(d) To negate a number (either a positive or negative one), invert all

the bits and add 1 to the result, ignoring overﬂow.

(e) 4-bit examples

i. 0000

= 0

ii. 0110

= 6

iii. 1010

= −6

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Cirrus Logic CS485 Manual de usuario Pagina 9