#     Function INTEGER-LENGTH

Syntax:

integer-length integer => number-of-bits

Arguments and Values:

integer---an integer.

number-of-bits---a non-negative integer.

Description:

Returns the number of bits needed to represent integer in binary two's-complement format.

Examples:

``` (integer-length 0) =>  0
(integer-length 1) =>  1
(integer-length 3) =>  2
(integer-length 4) =>  3
(integer-length 7) =>  3
(integer-length -1) =>  0
(integer-length -4) =>  2
(integer-length -7) =>  3
(integer-length -8) =>  3
(integer-length (expt 2 9)) =>  10
(integer-length (1- (expt 2 9))) =>  9
(integer-length (- (expt 2 9))) =>  9
(integer-length (- (1+ (expt 2 9)))) =>  10
```

Side Effects: None.

Affected By: None.

Exceptional Situations:

Should signal an error of type type-error if integer is not an integer.

Notes:

This function could have been defined by:

```(defun integer-length (integer)
(ceiling (log (if (minusp integer)
(- integer)
(1+ integer))
2)))
```

If integer is non-negative, then its value can be represented in unsigned binary form in a field whose width in bits is no smaller than (integer-length integer). Regardless of the sign of integer, its value can be represented in signed binary two's-complement form in a field whose width in bits is no smaller than (+ (integer-length integer) 1).      