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Arithmetic on Indices

This step applies only to color index and stencil index groups. If the index is a floating-point value, it is converted to fixed-point, with an unspecified number of bits to the right of the binary point. Indices that are already integers remain so; any fraction bits in the resulting fixed-point value are zero.

The fixed-point index is then shifted by bits, left if and right otherwise. In either case the shift is zero-filled. Then, the signed integer offset INDEX_OFFSET is added to the index.

David Blythe
Sat Mar 29 02:23:21 PST 1997