<< and <<= operators

(twinBASIC) Shifts the bits of a numeric value left by a given number of positions, filling vacated low-order bits with zero. The compound form «= shifts-and-assigns in one step.

Note

<< and <<= are twinBASIC extensions. Classic VBA has no bitshift operators; equivalent code multiplies by powers of two (x * 2, x * 4, …) and relies on overflow rules.

Syntax:

result = number « count
variable «= count

result
Any numeric variable.
variable
Any numeric variable or writable property.
number
An expression of an integral type: Byte, Integer, Long, LongLong or LongPtr. Other types are described below.
count
Any numeric expression giving the number of bit positions to shift.

The data type of result matches the type of number, whatever the type of count; shifts do not follow the promotion rules of the arithmetic operators. A shift by as many bits as the type holds, or more, yields 0 rather than wrapping: 1& << 32 is 0. The sign bit is not preserved — << is a logical left shift, equivalent to multiplication by 2count within the available width, with no overflow error: &H4000 << 1 is the Integer -32768. A negative count raises no error, but gives no useful result.

An integer literal with no type suffix is an Integer, so 1 << 20 shifts a 16-bit value and is 0. Write 1& << 20 to shift a Long and get 1048576.

Important

Only the integral types are shifted bit by bit. With other types of number:

  • A Currency or Decimal is shifted as a value, fraction included: a Currency or Decimal holding 7.9, shifted left by 1, is 15.8.
  • A Variant holding a fractional value is shifted the same way — a Variant holding the Double 7.9, shifted left by 1, is 15.8 — and a large count can give Empty: a Variant holding the Integer 1, shifted left by 20, is Empty.
  • A Single, Double, Date, Boolean or String compiles without a diagnostic, but the procedure containing the shift does not run: the IDE reports compilation (codegen) error detected at that line.

Convert such a value with CLng or CLngLng before shifting it.

Compound assignment

x <<= n is the twinBASIC shorthand for x = x << n. <<= is a statement, not an expression — it does not produce a value.

Dim Mask As Long = 1
Mask <<= 4                      ' Mask is now &H10 (16).
Mask <<= 4                      ' Mask is now &H100 (256).

Example 

Dim Value As Long
Value = 1 << 0                  ' Returns 1.
Value = 1 << 4                  ' Returns 16.
Value = 3 << 8                  ' Returns 768.
Value = 1& << 33                ' Returns 0 (shift exceeds Long width).
Value = 1 << 20                 ' Returns 0: the literal 1 is an Integer.
Value = 1& << 20                ' Returns 1048576.

See Also