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Left Shift Assignment Operator (<<=)

Left shifts the value of a variable by the number of bits specified in the value of an expression and assigns the result to the variable.

result <<= expression


Any numeric variable.
Any numeric expression.


Using this operator is almost the same as specifying result = result << expression, except that result is only evaluated once.

The <<= operator shifts the bits of result left by the number of bits specified in expression. The operator masks expression to avoid shifting result by too much. Otherwise, if the shift amount exceeded the number of bits in the data type of result, all the original bits would be shifted away to give a trivial result. To ensure that each shift leaves at least one of the original bits, the shift operators use the following formula to calculate the actual shift amount: mask expression (using the bitwise AND operator) with one less than the number of bits in result.


For example:

var temp
temp = 14
temp <<= 2 

The variable temp has a value of 56 because 14 (00001110 in binary) shifted left two bits equals 56 (00111000 in binary). Bits are filled in with zeroes when shifting.

To illustrate how the masking works, consider the following example.

var x : byte = 15;
// A byte stores 8 bits.
// The bits stored in x are 00001111
x <<= 10;
// Actual shift is 10 & (8-1) = 2
// The bits stored in x are 00111100
// The value of x is 60
print(x); // Prints 60


Version 1

See Also

Bitwise Left Shift Operator (<<) | Bitwise Right Shift Operator (>>) | Unsigned Right Shift Operator (>>>) | Assignment Operator (=) | Operator Precedence | Operator Summary