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| Allegro CL version 9.0 Unrevised from 8.2 to 9.0. 8.2 version

## read-tiny-float

Arguments: string &key (return-zero t)

This is a convenience function which allows users to read a small-magnitude float safely (that is, without floating-point-underflow errors). If the float is smaller in magnitude than the least-positive float of the appropriate format, then zero in the appropriate form (in the appropriate format) is returned by default, or, if the return-zero keyword argument is specified as `nil`, the least-positive or elast negative float of the appropriate format is returned.

string must be a string whose contents read as a single floating-point number. It is an error resulting in undefined behavior if there is more in the string than the representation of a sinlge floating point number. (The function decides on whether the resulting float is positive or negative based on the presence and location of a \#- charater. Such characters after the float representation could result in an incorrect value. If string represents a float larger than the least positive float or smaller than the least negative, the read is as if done by read-from-string. No protection is provided against floating-point-overflow errors.

### Example

    ;;  This function is intended to allow for forms like the following:
    ;;  (defconstant *app-single-eps*
    ;;               (max least-positive-single-float 1.0e-50))
    ;;  LEAST-POSITIVE-SINGLE-FLOAT is 1.0e-45, so that is the desried value
    ;;  but reading 1.0e-50 may cause a floating-point-underflow error.
    ;;  That can be protected against with this form:
    ;; (defconstant *app-single-eps*
    ;;              (max least-positive-single-float
    ;;                   (read-tiny-float "1.0e-50")))
    ;;
    ;;  In the reamining examples, we assume *read-default-float-format*
    ;;  is single-float.
    ;;
    (read-tiny-float "1.0") RETURNS 1.0
    (read-tiny-float "1.0e-50") RETURNS 0.0
    (read-tiny-float "1.0e-50" :return-zero nil) RETURNS 1.0e-45
            ;; i.e. least-positive-single-float
    (read-tiny-float "-1.0e-50" :return-zero nil) RETURNS -1.0e-45
            ;; i.e. least-negative-single-float
    (read-tiny-float "-1.0d-50" :return-zero nil) RETURNS -1.0d-50
    (read-tiny-float "-1.0d-550" :return-zero nil) RETURNS -5.0d-324
            ;; i.e. least-negative-double-float

See Floating-point infinities and NaNs, and floating-point underflow and overflow in implementation.htm for more information and sample handler code to cath the errors.

Copyright (c) 1998-2019, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 8.2 page.
Created 2012.5.30.

|  | ToC | DocOverview | CGDoc | RelNotes | FAQ | Index | PermutedIndex
| Allegro CL version 9.0 Unrevised from 8.2 to 9.0. 8.2 version