Floor/ceiling horizontal span drawing was occasionally spilling over by one pixel. For example, a vertical line of pixels from a floor on the player's right would appear on the left edge of the screen.
The rightmost pixel of a span sometimes went outside bounds of texture, causing corruption.
Also more strict checking for divide by zero, and cleanup of function.
Floor/ceiling horizontal span drawing was occasionally spilling over by one pixel. For example, a vertical line of pixels from a floor on the player's right would appear on the left edge of the screen. The rightmost pixel of a span sometimes went outside bounds of texture, causing corruption. Also more strict checking for divide by zero, and cleanup of function.