description

# toSigned method Null safety

BigInt toSigned (

1. int width

)

Returns the least significant `width` bits of this integer, extending the highest retained bit to the sign. This is the same as truncating the value to fit in `width` bits using an signed 2-s complement representation. The returned value has the same bit value in all positions higher than `width`.

    var big15 = new BigInt.from(15);
    var big16 = new BigInt.from(16);
    var big239 = new BigInt.from(239);
                                         V--sign bit-V
    big16.toSigned(5) == -big16   //  00010000 -> 11110000
    big239.toSigned(5) == big15   //  11101111 -> 00001111
                                         ^           ^

This operation can be used to simulate arithmetic from low level languages. For example, to increment an 8 bit signed quantity:

    q = (q + 1).toSigned(8);

`q` will count from `0` up to `127`, wrap to `-128` and count back up to `127`.

If the input value fits in `width` bits without truncation, the result is the same as the input. The minimum width needed to avoid truncation of `x` is `x.bitLength + 1`, i.e.

    x == x.toSigned(x.bitLength + 1);

## Implementation

    BigInt toSigned(int width);