[Haskell-cafe] ANNOUNCE: floatshow-0.1 faster String representations for Double and Float
daniel.is.fischer at googlemail.com
Mon Apr 18 23:36:17 CEST 2011
The Show instances for RealFloat types provided in base are very elegant,
as they produce the shortest string which 'read' converts back to the
original number. That, however, involves a check after each digit has been
determined and arithmetic of usually fairly large Integers, which makes
these Show instances rather slow.
For cases where having the conversion fast is more important than having it
produce elegant output, the floatshow package provides alternative
conversions, which avoid the checks and reduce the occurrences of large
Integers by just producing a sufficiently long output string.
The speed gain can be substantial if the numbers have exponents of large
absolute modulus, but for the more common case of numbers whose exponents
have small absolute modulus, the difference is (although still significant
for Double) too small in my opinion to seriously consider replacing the
Show instances. Therefore I've put these functions into their own package.
In my benchmarks, the speed gain ranges from 4x to 10x for Double and from
1.25x to 5x for Float, so the package may be a useful alternative for tasks
requiring the output of many floating point numbers.
Sadly, floatshow is non-portable and requires ghc >= 6.12.
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