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Routines |
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Used by the routines at ObjectPlacement_SpecialTerrain, InitialiseLevel, ContextualRandomNumber, 709D, InitialiseNewLevel and DemoModeInput.
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Random numbers are just data pulled from addresses between 7900-7AFF (sequentially).
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| GetRandomNumber | 6400 | PUSH HL | Stash HL on the stack. | |||||
| 6401 | LD HL,($781E) | HL=*RandomNumberSeed. | ||||||
| 6404 | LD A,(HL) | A=*HL. | ||||||
| 6405 | INC L | Increment L by one. | ||||||
| 6406 | JR NZ,UpdateRandomNumberSeed | Jump to UpdateRandomNumberSeed if L is not zero. | ||||||
| 6408 | INC H | Increment H by one. | ||||||
| 6409 | BIT 2,H | Jump to UpdateRandomNumberSeed if bit 2 of H is not set. | ||||||
| 640B | JR Z,UpdateRandomNumberSeed | |||||||
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Bit 2 is set, this means that H has reached 7C so pull the range back down to 79.
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| 640D | LD H,$79 | H=79. | ||||||
| UpdateRandomNumberSeed | 640F | LD ($781E),HL | Write HL to *RandomNumberSeed. | |||||
| 6412 | POP HL | Restore HL from the stack. | ||||||
| 6413 | RET | Return. | ||||||
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