CIRCEXT Implementation

The implementation of the circle extension is straightforward with one exception. After standard housekeeping chores are completed (determining size, saving data segment, clearing playground), it extracts the radius argument. A for loop over 2pi is used to plot a circle using sin() and cos() to determine coordinates. The pixel is plotted using the COORD macro to convert cartesian coordiantes into the index of the picture array.

What is tricky is that the floating point emulation library needs access to the original data segment. Thus, before the sin() and cos() calls are made, a asm mov ds, oldseg is used to restore the original datasegment, and a corresponding asm mov ds, myseg is used afterwards to return to the extension segment. This issue is documented above in Data Segments.