Output of arb_vertex_type_2_10_10_10_rev-array_types from piglit tests:

testing: RGBA SINT
testing: RGBA SNORM
Probe color at (25,5)
  Expected: 0.500000 0.250000 0.000000 1.000000
  Observed: 0.501961 0.250980 0.000000 0.333333
testing: RGBA UINT
testing: RGBA UNORM
testing: BGRA SNORM
Probe color at (85,5)
  Expected: 0.000000 0.250000 0.500000 1.000000
  Observed: 0.000000 0.250980 0.501961 0.333333
testing: BGRA UNORM
Mesa version 17.3.3
AMD/ATI Barts PRO Radeon HD 6850

Detail in https://github.com/supertuxkart/stk-code/issues/3097, this bug cause
wrong animation in stk.

And i think 2.2 / 2.3 equation isn't causing this bug, because from what i see
zero is represented correctly in stk, also some amd devs told me barts switched
to use the new formula long time ago.

Any idea?