Submitted by Steve Fewell
Name: Integer DIV routine
Starting Address: &9FFD
Entry criteria: Either IWA or FWA contain the dividend. A contains the variable type (Floating-Point/Integer). The Basic Text Pointer 2 points to an expression (the divisor) [e.g. " A%"]
Exit: The IWA.= Quotient (Result, IWA = IWA / Divisor-expression).
Call the Integer Division routine to evaluate the Divisor-expression and perform the actual division.
Multiply the Result by the base (Base 2 - Binary) and add on any value needing to be added to the result. This is not done by the Integer Division routine due to time constraints, as the MOD routine does not need to perform these tasks in order to obtain its required remainder.
Push the sign-bit of the result to the 6502 stack, load X with &39 (to specify where the result is located), and call the end of the Integer multiplication routine to put the Result into the IWA, convert it to the correct sign, and to check the next operator to see if any further multiplication/division processing is required.
Disassembly for the Integer DIV routine
|9FFD||032 249 128||20 F9 80||JSR &80F9 Integer Division|
|A000||&9||038 057||26 39||ROL &39|
|A002||&:||038 058||26 3A||ROL &3A|
|A004||&;||038 059||26 3B||ROL &3B|
|A006||&<||038 060||26 3C||ROL &3C|
|A008||$7||036 055||24 37||BIT &37|
|A00B||9||162 057||A2 39||LDX#&39|
|A00D||128 165||80 A5||BRA -91 --> &9FB4 Get Result from Zero Page & check next operator in expression|