1. A method comprising: using a programmable linear interpolator in a texture unit to calculate a dot product; determining that a dot product coefficient determined by the texture unit is negative and changing the sign of the coefficient to a positive value; and compensating for the sign change by passing a control mask for each of the texels with a negative coefficient to a texture control and determining that one value in the mask means that the corresponding coefficient is positive and another value in the mask means that the corresponding coefficient is negative.