[ Arithmetic | 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*
- Output: 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

### Exceptions

*(4) instantiation fault *
- Number1 or Number2 is not instantiated (non-coroutining mode only).
*(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.

## Examples

Success:
Result is 1 << 3. % gives Result = 8
Result is 5 << 1. % gives Result = 10
Result is 10 << -1. % gives Result = 5
Result is -5 << 1. % gives Result = -10
Error:
Result is 1.1 << 3. % type error

## See Also

is / 2