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Focus Energy glitch: Difference between revisions
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{{Misc R/B}}
The '''Focus Energy
Focus Energy is a move that, ever since [[bp:Generation II|Generation II]], increased the user's critical hit rate
In Generation I, due to a bug, Focus Energy will always effectively quarter the player's chances of getting a critical hit.
This glitch was fixed in [[bp:Pokémon Stadium|Pokémon Stadium]], where Focus Energy quadruples the critical hit rate instead.
==Further analysis==
The relevant block of code for Focus Energy's effect is this, beginning at offset 3E055 in Pokémon Red and Blue (view 0F:6055 in a debugger). Thanks Wack0 for walking through this.
bit 2, a ; test for focus energy<br/>
jr nz, .focusEnergyUsed (6061)<br>
sla b ; b=b*2<br>
jr nc, .noFocusEnergyUsed ; if b was below 128, skip...<br>
ld b, $ff ; a cap at 255/256<br>
jr .noFocusEnergyUsed<br>
.focusEnergyUsed<br>
srl b ; whoops! b=b/2, and if you look, the jump to here is before the b=b*2, so b is effectively 1/4 of what it should be<br>
.noFocusEnergyUsed ; no cap at 255/256 for focus energy. I wonder if, if done properly, this would have caused bugs related to integer wraparound..<br>
; ... (check for high critical hit move here)<br>
The relative jump to '.focusEnergyUsed' that happens when Focus Energy is used makes the game skip a 'sla b' (double b), and then a 'srl b' (half b) at '.focusEnergyUsed' halves the value in register 'b'.
If Focus Energy is not used, the value in 'b' is doubled and if it was used, the value in 'b' is halved. 2.0/0.5=4.0, meaning critical hits land four times less likely.
[[Category:Generation I glitches]]
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