[ Arithmetic | The ECLiPSe Built-In Predicates | Reference Manual | Alphabetic Index ]

# <<(+Number1, +Number2, -Result)

Shifts Number1 left by Number2 bits and unifies the resulting value with Result.

Number1
  Integer.
Number2
  Integer.
Result
  A variable or integer.

## Description

This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to <<(Number1, Number2, Result) is equivalent to

        Result is Number1 << Number2

which should be preferred for portability.

The shift behaves as if operating on an unlimited length two's complement representation. Shifting by a negative amount is the same as shifting by the same positive amount in the other direction.

In coroutining mode, if Number1 or Number2 are uninstantiated, the call to <</3 is delayed until these variables are instantiated.

### Modes and Determinism

- <<(+, +, -) is det

### Exceptions

(4) instantiation fault
  Number1 or Number2 is not instantiated (non-coroutining mode only).
(5) type error
  Result is a number but not an integer.
(5) type error
  Number1 or Number2 is a number but not an integer.
(24) number expected
  Number1 or Number2 is not of a numeric type.
(24) number expected
  Result is neither a number nor a variable.

## Examples

    Success:
          <<(1, 3, 8).
    Fail:
          <<(1, 2, 3).
    Error:
          <<(A, 2, 6).              (Error 4).
          <<(6, 2.0, 24.0).         (Error 5).
          <<(4 + 2, 2, 24).         (Error 24).
          <<(5, 2, r).              (Error 24).

## See Also

is / 2