NAME¶

fpclassify - Floating point number classification of Tcl values

SYNOPSIS¶

package require tcl 8.7

fpclassify value

DESCRIPTION¶

The fpclassify command takes a floating point number, value, and returns one of the following strings that describe it:

zero

value is a floating point zero.

subnormal

value is the result of a gradual underflow.

normal

value is an ordinary floating-point number (not zero, subnormal, infinite, nor NaN).

infinite

value is a floating-point infinity.

nan

value is Not-a-Number.

The fpclassify command throws an error if value is not a floating-point value and cannot be converted to one.

EXAMPLE¶

This shows how to check whether the result of a computation is numerically safe or not. (Note however that it does not guard against numerical errors; just against representational problems.)

set value [command-that-computes-a-value]
switch [fpclassify $value] {


    normal - zero {


        puts "Result is $value"


    }


    infinite {


        puts "Result is infinite"


    }


    subnormal {


        puts "Result is $value - WARNING! precision lost"


    }


    nan {


        puts "Computation completely failed"


    }
}

SEE ALSO¶

expr(3tcl), mathfunc(3tcl)

KEYWORDS¶

floating point

STANDARDS¶

This command depends on the fpclassify() C macro conforming to “ISO C99” (i.e., to ISO/IEC 9899:1999).

COPYRIGHT¶

Copyright © 2018 Kevin B. Kenny <kennykb@acm.org>. All rights reserved