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Special Reference: Shiny Hunting

Due to the newly risen discussion about the so-called Shiny Hunting and the postulation of some people to prove the validity of 'Shiny Hunting', I now post a reference about this concern.

Since all these doubting people want a 'technical statement', the following won't be easy to understand if you don't like numbers, probabilities and computer-terms. So if you are just another pokemon player who tries to find 'the final answer' to why-the-hell-don't-i-get-any-single-shiny-with-this-tactic (which is btw 42, as you all know) then quit reading here.

Warning: After reading this document some people will have to accept a 'uncomfortable' truth. Don't go on if you can't live with the existence of 'Shiny Hunting'. (Yes, I'm a little bit sarcastic atm. -.-)

Okay. And here it comes. This is the routine which is responsible for the decision if the pokemon is a Shiny: (I added some comments for you...)

ROM:0205E40C SpecialShinyHandler                     ; CODE XREF: CheateChainSet+5Cp
ROM:0205E40C                 PUSH    {R3-R5,LR}       ; r0 == chainsize
ROM:0205E40E                 CMP     R0, #0           ; if equal 0 then no special shiny handling  
ROM:0205E40E                                            - the normal 1 out of 8192 chance is used
ROM:0205E410                 BNE     loc_205E416
ROM:0205E412                 MOV     R0, #0
ROM:0205E414                 POP     {R3-R5,PC}      ; exit in case of chainsize == 0
ROM:0205E416 ; ---------------------------------------------------------------------------
ROM:0205E416
ROM:0205E416 loc_205E416
ROM:0205E416                 ADD     R2, R0, #0      ; r2 = r0 = chainsize
ROM:0205E418                 MOV     R1, #0xC8       ; r1 = 0xC8 = 200
ROM:0205E41A                 LDR     R0, =0x2008     ; r0 = 0x2008 = 8200
ROM:0205E41C                 MUL     R2, R1          ; r2 = chainsize * 200
ROM:0205E41E                 SUB     R5, R0, R2      ; r5 = 8200 - r2
ROM:0205E420                 CMP     R5, #0xC8
ROM:0205E422                 BGE     loc_205E426
ROM:0205E424                 ADD     R5, R1, #0      ; prevent negative value if chainsize
ROM:0205E424                                           is bigger than 40
ROM:0205E426
ROM:0205E426 loc_205E426
ROM:0205E426                 LSL     R0, R5, #0x10
ROM:0205E428                 LSR     R0, R0, #0x10   ; overflow secure
ROM:0205E42A                 BNE     loc_205E430
ROM:0205E42C                 BL      IgnoreMe        ; never executed
ROM:0205E430
ROM:0205E430 loc_205E430
ROM:0205E430                 LSL     R0, R5, #0x10
ROM:0205E432                 LSR     R0, R0, #0x10   ; prevent overflow
ROM:0205E434                 CMP     R0, #1
ROM:0205E436                 BHI     loc_205E43C     ; r0 is always > 1, so jump
ROM:0205E438                 MOV     R4, #0
ROM:0205E43A                 B       loc_205E46A
ROM:0205E43C ; ---------------------------------------------------------------------------
ROM:0205E43C
ROM:0205E43C loc_205E43C
ROM:0205E43C                 BL      get_random_val  ; Get a randomized value between 0 and 65535
ROM:0205E440                 ADD     R4, R0, #0      ; r4 == rand
ROM:0205E442                 LSL     R1, R5, #0x10
ROM:0205E444                 LDR     R0, =0xFFFF     ; r0 == 0xFFFF == 65535
ROM:0205E446                 LSR     R1, R1, #0x10
ROM:0205E448                 BLX     div_r0_r1       ; 65535 / (8200 - chainsize * 200)
ROM:0205E44C                 ADD     R1, R0, #0
ROM:0205E44E                 ADD     R1, R1, #1      ; (65535 / (8200 - chainsize * 200)) + 1
ROM:0205E450                 LSL     R1, R1, #0x10
ROM:0205E452                 ADD     R0, R4, #0      ; r0 = rand
ROM:0205E454                 LSR     R1, R1, #0x10
ROM:0205E456                 BLX     div_r0_r1       ; rand / (65535 / (8200 - chainsize * 200)) + 1
ROM:0205E45A                 LSL     R0, R0, #0x10
ROM:0205E45C                 LSR     R4, R0, #0x10   ; r4 = r0 (r0 == lastresult)
ROM:0205E45E                 LSL     R0, R5, #0x10   
ROM:0205E460                 LSR     R0, R0, #0x10   ; r0 = (65535 / (8200 - chainsize * 200)) + 1
ROM:0205E462                 CMP     R4, R0
ROM:0205E464                 BCC     loc_205E46A     ; if r4 < r0 then jump
ROM:0205E466                 BL      IgnoreMe        ; this time it is executed but it doesn't
ROM:0205E466                                           change r4 so ignore it once again
ROM:0205E46A
ROM:0205E46A loc_205E46A
ROM:0205E46A
ROM:0205E46A                 CMP     R4, #0          ; last test. If r4 == 0 Then...
ROM:0205E46C                 BNE     loc_205E472
ROM:0205E46E                 MOV     R0, #1          ; ... make it SHINY!
ROM:0205E470                 POP     {R3-R5,PC}      ; return
ROM:0205E472 ; ---------------------------------------------------------------------------
ROM:0205E472
ROM:0205E472 loc_205E472
ROM:0205E472                 MOV     R0, #0         ; ... else: no shiny
ROM:0205E474                 POP     {R3-R5,PC}     
ROM:0205E474 ; End of function SpecialShinyHandler
ROM:0205E474
ROM:0205E474 ; ---------------------------------------------------------------------------
ROM:0205E476                 ALIGN 4
ROM:0205E478 dword_205E478   DCD 0x2008              ; DATA XREF: SpecialShinyHandler+Er
ROM:0205E47C dword_205E47C   DCD 0xFFFF              ; DATA XREF: SpecialShinyHandler+38r
ROM:0205E480 ; ---------------------------------------------------------------------------

Okay. That's the technical part. Let's analyze it the mathematical way. The basic formula is this one: (n is the chainsize)

It works for all cases of n between 0 and 40. If n is bigger than 40 the denominator is always 200.

After calculating this, a function, which returns a random number between 0 and 65535, is called. The random number (r) is divided by Z and afterwards the result has to be lower than 1. (It's a math.floor operation, so anything < 1 returns 0.)

Because r can be anything between 0 and 65535 the probality P is:

So, for the last time: NO, shiny hunting isn't a bug as many people state and YES, shiny hunting depends on the 'length' of your shiny chain.

Greetz
MX

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