[GRASS5] GRASS testsuite issue

[Sören Gebbert]

Dear list,
while developing the new GRASS testsuite, i noticed some unexpected behavior.

I try to validate the generated output of grass modules with md5 checksum tests.
I check the binary files in the grass location (cell, fcell, topo, coor and other files ). 
I was expecting the output of grass (raster, raster3d and vector) is equal on x86 machines,
but after some testing i recognized that the output differs.

If i create raster map's with r.mapcalc or r3.mapcalc and use sin() and cos(), the md5
checksums are differ between Linux AMD gcc-3.4.4 and Linux P4 gcc-4.0.3 systems.
The same with v.buffer. But the command "r.mapcalc test=10" produce's equal output. 

How could this happen? Have the compiler, libraries (math?) or other software influence of the
data generation, or is this a feature of the gislib?
Maybe the optimize funciton of gcc (-On, SSE, mmx, 3dnow and stuff) produce this behavior?
I dont know, but i need help. If there is no way no avoid this behavior, 
the md5 checksum test (an important feature) will not work :(  . 
A work-around may be: to check the output exported with the *.out.ascii modules?

What to do? Any help or suggestions?

Best regards
Soeren