Game Development Reference
In-Depth Information
0101 (0x5)
~(0101) = 1010 (0xA)
We can use the inversion operator to clear a particular bit or bits from a value, if we com-
bine the inversion operator with the AND operator.
unsigned int value = FLAG0 | FLAG1 | FLAG2 | FLAG4; // 00010111
const unsigned int mask = ~(FLAG4); // 11101111
value &= mask; // 00000111
6.1.5 Left Shift <<
The shift operators move bits by the number of positions specified, the left shift operator
will shift the bits from the low bit to the high bit, bits below the shift will be set to 0 and
the bits shifted beyond the type's size are lost.
00000001 << 2
= 00000100
Left shifting can be used as an efficient way of performing multiplications by powers of
two. Shifting a value left by n bits has the effect of multiplying it by 2
n
6.1.6 Right Shift >>
Therightshiftisexactlythesameastheleftshift,exceptarightshiftoperatorwillshiftthe
bits from the high bit towards the low bit
00001101 >> 2
= 00000011
A right shift by n bits can be used to perform division by 2
n
.
The
Alignment
sectionhasanexampleusecaseinwhichenumflagsareuseful.Alignment
is an operation which can be combined, for example it is possible to align one element to
both the top and the left edges of some rectangle. Using enum flags allows us to reduce
the amount of code that would be necessary if each possible combination were to be im-
plementedindividually,andtheduplicationofcodewouldmakeitdifficulttomaintainand
understand.
