Clozure CL Documentation

4.11. Floating Point Numbers

In Clozure CL, the Common Lisp types short-float and single-float are implemented as IEEE single precision values; double-float and long-float are IEEE double precision values. On 64-bit platforms, single-floats are immediate values (like fixnums and characters).

Floating-point exceptions are generally enabled and detected. By default, threads start up with overflow, division-by-zero, and invalid enabled, and the rounding mode is set to nearest. The functions SET-FPU-MODE and GET-FPU-MODE provide user control over floating-point behavior.

[Function]

get-fpu-mode &optional mode

Return the state of exception-enable and rounding-mode control flags for the current thread.

mode--- One of the keywords :rounding-mode, :overflow, :underflow, :division-by-zero, :invalid, :inexact.

If mode is supplied, returns the value of the corresponding control flag for the current thread.

Otherwise, returns a list of keyword/value pairs which describe the floating-point exception-enable and rounding-mode control flags for the current thread.

rounding-mode--- One of :nearest, :zero, :positive, :negative

overflow, underflow, division-by-zero, invalid, inexact --- If true, the floating-point exception is signaled. If NIL, it is masked.

[Function]

set-fpu-mode &key
      rounding-mode overflow underflow division-by-zero
      invalid inexact

Set the state of exception-enable and rounding-mode control flags for the current thread.

rounding-mode--- If supplied, must be one of :nearest, :zero, :positive, or :negative.

overflow, underflow, division-by-zero, invalid, inexact---NIL to mask the exception, T to signal it.

Sets the current thread's exception-enable and rounding-mode control flags to the indicated values for arguments that are supplied, and preserves the values assoicated with those that aren't supplied.