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Luck manipulation (Generation I): Difference between revisions
m
Incredible! No need to shorten this if it's well-organized, which it is. Just adding a category to it.
>Bbbbbbbbba (Added hard-reset manipulations. I guess this article is getting too long for first time readers... Cleanup is welcome.) |
>Sherkel m (Incredible! No need to shorten this if it's well-organized, which it is. Just adding a category to it.) |
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At the very beginning of the game's startup process (before the copyright screen), hRandomAdd ($FFD3) and hRandomSub ($FFD4) are zeroed with the entire HRAM; apart from that, Random_ is the only place in the code that directly changes them. If the exact timings and circumstances (actually only the carry flag matters) of those calls can be predicted (e.g. in a TAS or shortly after a hard reset), then the results can be predicted too. That's the principle behind luck manipulation.
==Advancement of the RNG==
Usually, the RNG is advanced (i.e. Random_ is called) whenever a random number is needed. In addition, it is also advanced once per frame during the V-Blank interrupt. Since the game doesn't need random numbers very often, the majority of RNG advancements come from the V-Blank.
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==DSum manipulation==
Two factors cause the DSum to change:
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* A change of rDIV between the two reads is comparatively rare, and doesn't affect the DSum much. <!-- TODO: Estimation of frequency? -->
In summary, '''the DSum decreases in the overworld, and increases during a battle, by about 0.5
===Application===
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#[http://wiki.pokemonspeedruns.com/index.php/Pok%C3%A9mon_Red/Blue/Yellow_DSum_Manipulation DSum manipulation FAQ on Pokémon Speedruns wiki]
#[https://github.com/pret/pokered/blob/6ba3765c5932996f5da6417ae703794ff10bb1cb/engine/random.asm random.asm]
[[Category:Non-glitch exploits]]
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