[RFC] libm replacement for Busybox

[Loïc Grenié]

     I've noticed that busybox uses few functions from libm.
  I've written some replacements for those functions. Right
  now this is just the test program and I've not made the
  effort of including them in Busybox. However I'd like to
  have your opinion: would it be a good idea to include
  them ?

    They are neither very fast nor very precise (the
  trigonometric functions are awful, up to 16 bits are
  false) but libm is rather large and usually a user of
  Busybox on an initrd or embedded platform does not
  need neither speed nor excellent precision. Otherwise
  it would always be possible to disable them anyway.

     Quick and dirty way to have a look:

cc -Wall -O2 -o libmtest libmtest.c -lm && ./libmtest
for f in err*
do
  tail -1 $f | sed "s/^/$f: /"|cut -f1-2
done

  The program does 10000 random tests for each of the 7
  functions included in the program (log,exp, pow, sin, cos,
  tan, atan2) and saves them in a (sorted) file. The first
  column is the log2() of the worst relative error of libmtest
  function against the same function of libm (i.e. the number
  of the first error bit in the mantissa) and the second field is
  the value of the arg. that provided the error (the error files are
  more complete -- for pow and atan2 there is a second
  argument but the for loop above does not print it even though
  it is present in the error file).

      Thanks,

           Loïc Grenié
-------------- next part --------------
A non-text attachment was scrubbed...
Name: libmtest.c
Type: text/x-csrc
Size: 11894 bytes
Desc: not available
Url : http://lists.busybox.net/pipermail/busybox/attachments/20081010/ea8c9ce8/attachment-0002.c