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Routines |
| Prev: 5F9A | Up: Map | Next: 5FC3 |
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Used by the routines at CreateSpawnedEntity, CreateRandomCreature, UpdatePickupEntity and UpdateScreen.
Makes a pseudo-random number by mixing the byte at a moving address in the game memory into a seed. The address moves on by one byte each time and wraps within 8000-9FFF.
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| GetRandomNumber | 5F9E | LD DE,($5F9A) | Fetch the seed. | |||||||
| 5FA2 | LD HL,($5F9C) | Fetch the address of the byte of game memory to mix in. | ||||||||
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Make the new low byte.
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| 5FA5 | LD A,(HL) | Fetch the byte of game memory. | ||||||||
| 5FA6 | ADD A,$05 | Add 05 to it. | ||||||||
| 5FA8 | LD B,A | Store the result in B. | ||||||||
| 5FA9 | LD A,($5CDE) | Fetch the game variable at GameVariable. | ||||||||
| 5FAC | ADD A,B | Add the byte from game memory. | ||||||||
| 5FAD | ADD A,E | Add the low byte of the seed. | ||||||||
| 5FAE | LD E,A | Make it the new low byte of the seed. | ||||||||
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Make the new high byte.
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| 5FAF | LD A,(HL) | Fetch the byte of game memory again. | ||||||||
| 5FB0 | CPL | Invert it. | ||||||||
| 5FB1 | ADD A,$16 | Add 16. | ||||||||
| 5FB3 | ADD A,D | Add the high byte of the seed. | ||||||||
| 5FB4 | ADD A,L | Add the low byte of the address. | ||||||||
| 5FB5 | LD D,A | Make it the new high byte of the seed. | ||||||||
| 5FB6 | LD ($5F9A),DE | Store the new seed. | ||||||||
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Move the address on.
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| 5FBA | INC HL | Move onto the next byte of game memory. | ||||||||
| 5FBB | LD A,H | Fetch the high byte of the address. | ||||||||
| 5FBC | AND %10011111 | Keep the address within 8000-9FFF. | ||||||||
| 5FBE | LD H,A | Put the high byte back. | ||||||||
| 5FBF | LD ($5F9C),HL | Store the address. | ||||||||
| 5FC2 | RET | Return. | ||||||||
| Prev: 5F9A | Up: Map | Next: 5FC3 |