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CONTRIBUTING.md
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CONTRIBUTING.md
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@ -15,10 +15,10 @@ The basic decompilation process is:
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* Repeat for each function until `asm/x.s` is empty.
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# For example, let's decompile `asm/cable_car.s`.
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# For example, let's decompile `asm/evilSpirit.s`.
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## 1. Create `src/cable_car.c`
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## 1. Create `src/evilSpirit.c`
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```c
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#include "global.h"
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@ -30,129 +30,127 @@ It must be the first include in the file. Other includes will assume you have in
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## 2. Include it in the rom
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Include `src/cable_car.c` in the rom by adding `src/cable_car.o` to `ld_script.ld`:
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Include `src/evilSpirit.c` in the rom by adding `src/evilSpirit.o` to `ld_script.ld`:
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```diff
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asm/battle_message.o(.text);
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asm/choose_party.o(.text);
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+ src/cable_car.o(.text);
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asm/cable_car.o(.text);
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asm/roulette_util.o(.text);
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asm/room.o(.text);
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asm/code_08080974.o(.text);
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+ src/evilSpirit.o(.text);
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asm/evilSpirit.o(.text);
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asm/houseDoorExterior.o(.text);
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```
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Do not remove `asm/cable_car.o(.text)`. We want both `src/cable_car.c` and `asm/cable_car.s` in the rom.
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Do not remove `asm/evilSpirit.o(.text)`. We want both `src/evilSpirit.c` and `asm/evilSpirit.s` in the rom.
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## 3. Translate the function to C
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Take the first function in `asm/cable_car.s`. Either comment it out or remove it, whichever is easier.
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Take the first function in `asm/evilSpirit.s`. Either comment it out or remove it, whichever is easier.
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```asm
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thumb_func_start sub_81231EC
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sub_81231EC: @ 81231EC
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push {r4,lr}
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lsls r0, 24
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lsrs r4, r0, 24
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ldr r0, _08123210 @ =gPaletteFade
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ldrb r1, [r0, 0x7]
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movs r0, 0x80
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ands r0, r1
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cmp r0, 0
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bne _0812320A
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ldr r0, _08123214 @ =sub_8123244
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bl SetMainCallback2
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adds r0, r4, 0
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bl DestroyTask
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_0812320A:
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pop {r4}
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pop {r0}
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bx r0
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thumb_func_start sub_08086284
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sub_08086284: @ 0x08086284
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push {r4, lr}
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adds r4, r0, #0
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ldr r1, _080862B4 @ =gUnk_08120668
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ldrb r0, [r4, #0xc]
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lsls r0, r0, #2
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adds r0, r0, r1
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ldr r1, [r0]
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adds r0, r4, #0
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bl _call_via_r1
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adds r1, r4, #0
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adds r1, #0x41
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movs r0, #0
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strb r0, [r1]
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adds r0, r4, #0
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adds r0, #0x76
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ldrh r1, [r0]
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adds r0, #4
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ldrh r2, [r0]
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adds r0, r4, #0
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movs r3, #0
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bl sub_0805EC9C
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pop {r4, pc}
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.align 2, 0
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_08123210: .4byte gPaletteFade
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_08123214: .4byte sub_8123244
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thumb_func_end sub_81231EC
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_080862B4: .4byte gUnk_08120668
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```
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---
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Then, start translating the code to `src/cable_car.c`, bit by bit:
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Then, start translating the code to `src/evilSpirit.c`, bit by bit:
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```asm
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lsls r0, 24
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lsrs r4, r0, 24
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push {r4, lr}
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adds r4, r0, #0
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```
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```c
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void sub_81231EC(u8 r4) {
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void sub_08086284(u8 *r4) {
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```
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---
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```asm
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ldr r0, _08123210 @ =gPaletteFade
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ldrb r1, [r0, 0x7]
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movs r0, 0x80
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ands r0, r1
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add r4, r0, #0
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ldr r1, _080862B4 @ =gUnk_08120668
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ldrb r0, [r4, #0xc]
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lsl r0, r0, #0x2
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add r0, r0, r1
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ldr r1, [r0]
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add r0, r4, #0
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bl _call_via_r1
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```
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```c
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r0 = (u8 *)(&gPaletteFade + 7) & 0x80;
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gUnk_08120668[*(u8 *)(r4 + 12)](r4);
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```
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---
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---
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```asm
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cmp r0, 0
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bne _0812320A
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add r1, r4, #0
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add r1, r1, #0x41
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mov r0, #0
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strb r0, [r1]
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```
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```c
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if (!r0) {
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*(u8 *)(r4 + 65) = 0;
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```
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---
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```asm
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ldr r0, _08123214 @ =sub_8123244
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bl SetMainCallback2
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add r0, r4, #0
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add r0, r0, #0x76
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ldrh r1, [r0]
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add r0, r0, #0x4
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ldrh r2, [r0]
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add r0, r4, #0
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mov r3, #0
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bl sub_0805EC9C
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```
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```c
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SetMainCallback2(&sub_8123244);
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sub_0805EC9C(r4, *(u16 *)(r4 + 118), *(u16 *)(r4 + 122), 0);
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```
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---
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```asm
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adds r0, r4, 0
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bl DestroyTask
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```
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```c
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DestroyTask(r4);
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```
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---
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```asm
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_0812320A:
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```
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```c
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}
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```
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---
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```asm
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pop {r4}
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pop {r0}
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bx r0
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pop {r4, pc}
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```
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```c
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return;
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```
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The type signature of the function depends on the return type.
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* `bx r0`: `void`
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* `bx r1`: `*`
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* `bx lr`: `void`, `*`
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* `pop {r4, pc}`: `void`
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* `adds {r0, r4}`
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`pop {r4, pc}`: `void`, `*`
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You will need to look at the caller and the function prologue to determine the exact type if not void.
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Since it used `bx r0`, it's `void` for sure.
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Since it only used `pop {r4, pc}`, it's probably `void`.
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---
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Putting it all together, we get:
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```c
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void sub_81231EC(u8 r4) {
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r0 = (u8 *)(&gPaletteFade + 7) & 0x80;
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if (!r0) {
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SetMainCallback2(&sub_8123244);
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DestroyTask(r4);
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}
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return;
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void sub_08086284(u8 *r4) {
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{
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gUnk_08120668[*(u8 *)(r4 + 12)](r4);
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*(u8 *)(r4 + 65) = 0;
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sub_0805EC9C(r4, *(u16 *)(r4 + 118), *(u16 *)(r4 + 122), 0);
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return;
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}
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```
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@ -162,63 +160,55 @@ void sub_81231EC(u8 r4) {
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This line doesn't look quite right.
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```c
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r0 = (u8 *)(&gPaletteFade + 7) & 0x80;
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gUnk_08120668[*(u8 *)(r4 + 12)](r4);
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```
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What is `gPaletteFade`? You can find out where stuff is with `git grep`:
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What is `r4`? Since this function corresponds to an entity, we should first try to assign r4 to an`Entity` struct.
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You can find out what this is with `git grep`:
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```sh
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git grep "gPaletteFade" include/
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git grep "Entity" include/
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```
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```grep
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include/palette.h:extern struct PaletteFadeControl gPaletteFade;
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include/entity.h:typedef struct Entity
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```
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So it's a struct called `PaletteFadeControl`. Let's look in `palette.h`:
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So it's a struct called `Entity`. Let's look in `entity.h`:
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```c
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struct PaletteFadeControl
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typedef struct Entity
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{
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u32 multipurpose1;
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u8 delayCounter:6;
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u16 y:5; // blend coefficient
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u16 targetY:5; // target blend coefficient
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u16 blendColor:15;
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u16 active:1;
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u16 multipurpose2:6;
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u16 yDec:1; // whether blend coefficient is decreasing
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u16 bufferTransferDisabled:1;
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u16 mode:2;
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u16 shouldResetBlendRegisters:1;
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u16 hardwareFadeFinishing:1;
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u16 softwareFadeFinishingCounter:5;
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u16 softwareFadeFinishing:1;
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u16 objPaletteToggle:1;
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u8 deltaY:4; // rate of change of blend coefficient
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};
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u32 *field_0x0;
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u32 * field_0x4;
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EntityType entityType;
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u8 action;
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u8 previousActionFlag;
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u8 parameter3;
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u8 field_0xf;
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u8 flags;
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...
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} Entity;
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```
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---
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What's the 7th byte in this struct?
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What's the 12th byte in this struct?
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```c
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u32 multipurpose1; // 0-3
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u8 delayCounter:6; // 4
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u16 y:5; // 5
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u16 targetY:5; // 5-6
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u16 blendColor:15; // 7
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u16 active:1; // 7
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u32 *field_0x0; //0-3
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u32 * field_0x4; //4-7
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EntityType entityType; //8-11
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u8 action; //12
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u8 previousActionFlag; //13
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```
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Byte 7 has both `.blendColor` and `.active`.
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---
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Okay, what's 0x80 mean? It's `0b10000000`, which is the highest bit in a byte.
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`.active` comes after, which means it's higher, but it's also only one bit, so it's a safe bet.
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The 12th byte belongs to `action`. We can substitute this in by replacing r4's parameter type and adding in the member names.
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```c
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r0 = gPaletteFade.active;
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void sub_08086284(Entity *r4) {
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gUnk_08120668[r4->action](r4);
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```
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Much better.
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@ -226,32 +216,18 @@ Much better.
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---
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```c
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void sub_81231EC(u8 r4) {
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r0 = gPaletteFade.active;
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if (!r0) {
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SetMainCallback2(&sub_8123244);
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DestroyTask(r4);
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}
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return;
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void sub_08086284(Entity *r4) {
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gUnk_08120668[r4->action](r4);
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r4->bitfield = 0;
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sub_0805EC9C(r4, *((u8 *)&r4->heldObjectPtr + 2), r4->itemCooldown, 0);
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return;
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}
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```
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Now the temp variable `r0` is a little pointless. We can simplify this to:
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```c
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void sub_81231EC(u8 taskId) {
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if (!gPaletteFade.active) {
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SetMainCallback2(&sub_8123244);
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DestroyTask(taskId);
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}
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}
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```
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Looks done, right?
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This function is pretty simple, so it doesn't need any comments right now.
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But what about `sub_8123244`? It's still not obvious what that function does. We can find out by decompiling it later.
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The second of the function that is called uses an offset right in the middle of `heldObjectPtr`. Something seems wrong.
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We can ignore this for now, since we can come back to that later.
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Right now we are just concerned with making the function match, even if it isn't pretty.
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## 5. Build
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@ -259,44 +235,41 @@ But what about `sub_8123244`? It's still not obvious what that function does. We
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make
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```
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```gcc
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src/cable_car.c: In function `sub_81231EC':
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src/cable_car.c:4: `gPaletteFade' undeclared (first use in this function)
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src/cable_car.c:4: (Each undeclared identifier is reported only once for each function it appears in.)
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src/cable_car.c:5: warning: implicit declaration of function `SetMainCallback2'
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src/cable_car.c:5: `sub_8123244' undeclared (first use in this function)
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src/cable_car.c:6: warning: implicit declaration of function `DestroyTask'
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src/evilSpirit.c: In function `sub_08086284':
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src/evilSpirit.c:5: `r4' undeclared (first use in this function)
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src/evilSpirit.c:5: `gUnk_08120668' undeclared (first use in this function)
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src/evilSpirit.c:5: (Each undeclared identifier is reported only once for each function it appears in.)
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src/evilSpirit.c:7: warning: implicit declaration of function `sub_0805EC9C'
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```
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We got some errors. We need to tell the compiler what `gPaletteFade`, `SetMainCallback2`, `sub_8123244`, and `DestroyTask` are.
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We got some errors. We need to tell the compiler what `gUnk_08120668`, `r4`, and `sub_0805EC9C` are.
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We know `gPaletteFade` is from `palette.h`. We can do the same with the others. Declare them above the function:
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We know `r4` is an `Entity`, which is from `entity.h`. We can declare this above the function:
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```c
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#include "palette.h"
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#include "main.h"
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#include "task.h"
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#include "entity.h"
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```
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The odd one out is `sub_8123244`, which is in `asm/cable_car.s`! What then?
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What about `gUnk_08120668` and `sub_0805EC9C`?
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```c
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void sub_8123244();
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extern void sub_0805EC9C();
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extern (*gUnk_08120668[99])(Entity *);
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```
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Normally, we would do `extern void sub_8123244();`, but it won't be `extern` when we're done this file.
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Now the compiler will look outside of this file for both of these. We can set the size of `gUnk_08120668`, a pointer array, to `99`, since it's size is irrelevant for now.
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---
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Now our file looks like this:
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```c
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#include "global.h"
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#include "palette.h"
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#include "main.h"
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#include "task.h"
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#include "entity.h"
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void sub_8123244();
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extern void sub_0805EC9C();
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extern (*gUnk_08120668[99])(Entity *);
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void sub_81231EC(u8 taskId) {
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if (!gPaletteFade.active) {
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SetMainCallback2(&sub_8123244);
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DestroyTask(taskId);
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}
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void sub_08086284(Entity *r4) {
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gUnk_08120668[r4->action](r4);
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r4->bitfield = 0;
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sub_0805EC9C(r4, *((u8 *)&r4->heldObjectPtr + 2), r4->itemCooldown, 0);
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return;
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}
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```
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@ -322,9 +295,9 @@ sha1sum: WARNING: 1 computed checksum did NOT match
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---
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If you forgot to remove the function from `asm/cable_car.s`, you will get this error:
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If you forgot to remove the function from `asm/evilSpirit.s`, you will get this error:
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```gcc
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asm/cable_car.o: In function `sub_81231EC':
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(.text+0x0): multiple definition of `sub_81231EC'
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src/cable_car.o:(.text+0x0): first defined here
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asm/evilSpirit.o: In function `sub_08086284':
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(.text+0x0): multiple definition of `sub_08086284'
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src/evilSpirit.o:(.text+0x0): first defined here
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```
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