fpclassify - Floating point number classification of Tcl values
package require tcl 8.7
fpclassify value
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.
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"
}
}
This command depends on the fpclassify() C macro conforming to
“ISO C99” (i.e., to ISO/IEC 9899:1999).
Copyright © 2018 by Kevin B. Kenny <kennykb@acm.org>. All rights reserved