

Quality comparison of floating-point maths libraries - TalGalili
http://www.r-bloggers.com/quality-comparison-of-floating-point-maths-libraries/

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mturmon
From TFA:

"The results for R/Linux C were almost identical and a quick check of the R
source tree showed that R calls the C library function to evaluate log"

thus making the whole article an exercise in redundancy.

~~~
andrewf
Not entirely; it means the comparison was effectively between single-precision
and double-precision logs from the C library.

~~~
mturmon
Were they not both calling the normal double-precision log function in libm?

Sure, the linked article scans all the single-precision floats in a certain
range to do the test, but the function eventually called (using that list of
floats) is log in libm.

In any event, no discrepancy is noted, so what was the point?

Additionally, TFA does not make clear that there should be no errors in the
computed function affecting more than the least sig bit. It uses absolute
errors (up to 50 e-17) rather than looking at the relative error (or ULP, in
the jargon). It seems like a mess.

Here's a link with much more useful information:

[http://www.gnu.org/s/libc/manual/html_node/Errors-in-Math-
Fu...](http://www.gnu.org/s/libc/manual/html_node/Errors-in-Math-
Functions.html)

------
ars
With a little research they would have seen that the source of the math
library is actually: <http://www.moshier.net/#Cephes>

Another common library is: <http://www.ibm.com/software/awdtools/mass/> and
<http://www.ibm.com/systems/software/essl/> both from IBM.

Writing good math libraries is a huge undertaking, and there aren't that many
versions out there.

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kakali
Isn't the printf also introducing a rounding error? This all seems like a
futile test.

