miller@uiucdcs.UUCP (miller ) (02/03/84)
#N:uiucdcs:36100035:000:1127
uiucdcs!miller Feb 2 16:01:00 1984
This is the second installment of how to use Basic's floating point sub-
routines from assembly language on the c64. This time: protocol.
There are two floating point "registers" on the machine, F1 and F2. F1 is
located at $61-$66 (97-102) and F2 at $69-$6E (105-110). These registers are
used for all of the floating point math routines. Values are stored in each of
the six bytes in the format described last time.
In addition, there is a sign comparison flag located at $6F (111). If the
high order bit is set, it means that F1 and F2 are of different signs.
Subroutines may be executed by a JSR to the indicated address.
Parameters are passed in and out of the routines through F1, F2, and sometimes
other memory locations. When other locations must be specified, they are in
what we will call standard format (SF). SF means that memory addresses are
passed through the A (LSB) and the Y (MSB) registers.
Well, that's about all. Next time, I'll give you the actual calling
addresses of the subroutines along with a description of what they do. Stay
tuned...
A. Ray Miller
Univ Illinois