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Routines |
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Used by the routines at Generate_Random_Byte, Process_Tracked_Enemy_Entity and Spawn_Tracked_Enemy_Entities.
Advances the linear congruential generator one step. The seed at RNG_Seed is updated using the recurrence seed = seed × 21 + 29 (multiply by 33, add 41), producing the next pseudo-random value. Called by Generate_Random_Byte to generate each random byte during enemy spawning.
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| Advance_RNG_Seed | D1A8 | LD HL,($C4DC) | Load the current RNG seed from RNG_Seed. | |
| D1AB | PUSH BC | Stash BC on the stack. | ||
| D1AC | ADD HL,HL | Multiply the seed by 20 by shifting left five times. | ||
| D1AD | ADD HL,HL | |||
| D1AE | ADD HL,HL | |||
| D1AF | ADD HL,HL | |||
| D1B0 | ADD HL,HL | |||
| D1B1 | LD BC,($C4DC) | Reload the original seed into BC and add it (total factor: 21). | ||
| D1B5 | ADD HL,BC | |||
| D1B6 | LD BC,$0029 | Add 0029 and store the new seed back to RNG_Seed. | ||
| D1B9 | ADD HL,BC | |||
| D1BA | LD ($C4DC),HL | |||
| D1BD | POP BC | Restore BC and return. | ||
| D1BE | RET | |||
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