[Gegl-developer] Building GEGL fails on 64 bit Linux system

[scl <scl gplus gmail com>]

Hi,

I'm stuck on building GEGL on a 64 bit Debian Wheezy system.
The autogen.sh and make step are ok, but make check shows some tests 
with flaws or failing:
run-edge-laplace-broken.xml.sh: little differences, but tolerated
run-pixelize.xml.sh: little differences, but tolerated
run-gamma.xml.sh: failing
Below you find the result of autogen and the failing part of make check.
As I found out the reason is the glibc function 'powf' being inaccurate
on 64-bit systems, see also the GEGL bugreport [1] and the links there.

I'd like to get the failing test passing and already tried the following 
without success:
- calling pow and casting to gfloat:
#define powf(a,b) ((gfloat)pow(a,b))
- calling the GCC builtin powf function in gamma.c, if compiled on GCC:
#ifdef __GNUC__
#define powf(a,b) __builtin_powf(a,b)
#endif
- forcing the compiler to use another (hopefully working) math lib:
export LIBS="-lm"
- forcing the compiler not to use a C99 compliant powf function:
deactivate 'export CFLAGS="-std=gnu99"'
- using a binary, older glibc (libc6_2.7-18lenny7_amd64.deb):
even simple shell commands refuse to work now because of missing GLIBC 
symbols
- building an older glibc from scratch (glibc-2.11.3) and installing it
to GEGLs $INSTALL_PREFIX: the glibc build fails for unmatching binutils
and installing binutils-gold doesn't help.

Now I'm stuck and need your help. If somebody could give me the right
clue (preferably this week, if possible) would be very fine.

Thanks in advance and kind regards,

Sven

[1] https://bugzilla.gnome.org/show_bug.cgi?id=666417

***************************
Result of autogen:
------------------
Optional features:
  GEGL docs:       yes
  Build workshop:  no
  Build website:   yes
  SIMD:            sse:yes mmx:yes
  Vala support:    yes

Optional dependencies:
  asciidoc:        yes
  enscript:        yes
  Ruby:            yes
  Lua:             yes
  Cairo:           yes
  Pango:           yes
  pangocairo:      yes
  GDKPixbuf:       yes
  JPEG:            yes
  PNG:             yes
  OpenEXR:         yes
  rsvg:            yes
  SDL:             yes
  openraw:         yes
  Jasper:          yes
  graphviz:        yes
  avformat:        yes
  V4L:             no
  spiro:           yes
  EXIV:            yes
  umfpack:         yes


Failing part of make check:
---------------------------
make[4]: Entering directory 
`/var/lib/jenkins/workspace/gegl-distcheck-master/tests/compositions'
[...]
/var/lib/jenkins/workspace/gegl-distcheck-master/tests/compositions/reference/gamma.png 
and 
/var/lib/jenkins/workspace/gegl-distcheck-master/tests/compositions/output/gamma.png 
differ
  wrong pixels   : 18160/31680 (57.32%)
  max Δe         : 30.400
  avg Δe (wrong) : 1.439(wrong) 0.825(total)
FAIL: run-gamma.xml.sh
[...]
make[4]: *** [check-TESTS] Error 1
make[4]: Leaving directory 
`/var/lib/jenkins/workspace/gegl-distcheck-master/tests/compositions'
make[3]: *** [check-am] Error 2
make[3]: Leaving directory 
`/var/lib/jenkins/workspace/gegl-distcheck-master/tests/compositions'
make[2]: *** [check-recursive] Error 1
make[2]: Leaving directory 
`/var/lib/jenkins/workspace/gegl-distcheck-master/tests/compositions'
make[1]: *** [check-recursive] Error 1
make[1]: Leaving directory 
`/var/lib/jenkins/workspace/gegl-distcheck-master/tests'
make: *** [check-recursive] Error 1