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Universe: Ze

[BBC Master version]

Name: Ze [Show more] Type: Subroutine Category: Universe Summary: Initialise the INWK workspace to a hostile ship Deep dive: Fixing ship positions
Context: See this subroutine in context in the source code Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * DEATH calls Ze * GTHG calls Ze * Main game loop (Part 3 of 6) calls Ze * Main game loop (Part 4 of 6) calls Ze

Specifically, this routine does the following: * Reset the INWK ship workspace * Set the ship to a fair distance away in all axes, in front of us but randomly up or down, left or right * Give the ship a 4% chance of having E.C.M. * Set the ship to hostile, with AI enabled This routine also sets A, X, T1 and the C flag to random values. Note that because this routine uses the value of X returned by DORND, and X contains the value of A returned by the previous call to DORND, this routine does not necessarily set the new ship to a totally random location. See the deep dive on "Fixing ship positions" for details.
.Ze JSR ZINF \ Call ZINF to reset the INWK ship workspace JSR DORND \ Set A and X to random numbers STA T1 \ Store A in T1 AND #%10000000 \ Extract the sign of A and store in x_sign STA INWK+2 TXA \ Extract the sign of X and store in y_sign AND #%10000000 STA INWK+5 LDA #25 \ Set x_hi = y_hi = z_hi = 25, a fair distance away STA INWK+1 STA INWK+4 STA INWK+7 TXA \ Set the C flag if X >= 245 (4% chance) CMP #245 ROL A \ Set bit 0 of A to the C flag (i.e. there's a 4% \ chance of this ship having E.C.M.) ORA #%11000000 \ Set bits 6 and 7 of A, so the ship is hostile (bit 6 \ and has AI (bit 7) STA INWK+32 \ Store A in the AI flag of this ship \ Fall through into DORND2 to set A, X and the C flag \ randomly