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float

float Function

Syntax:

float number &optional prototype ! float

Arguments and Values:

number—a real.

prototype—a float.

float—a float.

Description:

float converts a real number to a float.

If a prototype is supplied, a float is returned that is mathematically equal to number but has the same format as prototype.

If prototype is not supplied, then if the number is already a float, it is returned; otherwise, a float is returned that is mathematically equal to number but is a single float.

Examples:

(float 0) *!* 0.0 
(float 1 .5) *!* 1.0 
(float 1.0) *!* 1.0 
(float 1/2) *!* 0.5 
<i>!</i> 1.0d0 <i><sub>or</sub></i> 
*!* 1.0 
(eql (float 1.0 1.0d0) 1.0d0) *! true*


See Also:

coerce

Expanded Reference: float​

Converting integers and ratios to floats​

float converts a real number to a single float when no prototype is supplied.

(float 0)
=> 0.0
(float 1)
=> 1.0
(float 1/2)
=> 0.5
(float 1/3)
=> 0.33333334

Float is identity for float inputs​

If the argument is already a float and no prototype is given, the same float is returned.

(float 1.0)
=> 1.0
(float 3.14)
=> 3.14

Using a prototype to control float format​

The optional second argument specifies the desired float format by example. The result will have the same float format as the prototype.

(float 1 1.0)
=> 1.0
(float 1 1.0d0)
=> 1.0d0
(float 1/3 1.0d0)
=> 0.3333333333333333d0

;; Verify the format matches the prototype
(eql (float 1.0 1.0d0) 1.0d0)
=> T

Converting pi to different precisions​

float is useful for converting constants to a specific float format.

(float pi 1.0)
=> 3.1415927
(float pi 1.0d0)
=> 3.141592653589793d0

Practical use: ensuring float arithmetic​

When you need floating-point division rather than rational division, convert one operand.

;; Rational division
(/ 1 3)
=> 1/3

;; Floating-point division
(/ (float 1) 3)
=> 0.33333334