fix the -g/O3 discrepancy for 32bit compile
fix the -g/O3 discrepancy for 32bit compile

in debug mode, some float operations see their intermediate
values stored in memory rather than staying in the FPU (which
is 80bit precision).

Several fixes are possible (breaking long calculations into
atomic steps for instance), but simpler of all is just about
turning the cost[] array into float* instead of double*.

The code is a tad faster, and i didn't see any major output
size difference.

Change-Id: Icf1f833e15f8ee4ecc7f9a521d07fdc96ef711aa

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