When the keyframes at either end of the source curve don't lie on exact frame boundaries,
this casued problems with the Cycles F-Modifier, as part of the cycle would get chopped
off.
This was caused by float -> integer truncation that was occurring, since one variable
was of the wrong type. The problem here wasn't discovered until now (thanks to gcc's
invalid-type warnings on printf's) as in standard usage, we can safely assume that all
keyframes are strictly on frame boundaries.
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