Quick reverse-engineering of OSScreenSetBufferEx. 5.5.1.

OSScreenSetBufferEx.c

int globalVar; //This could be anything, likely a struct?
//Feels like a stack pointer.
//unk_10098EB4

void OSScreenSetBufferEx(int bufferNum, void* address) {
	int r0 = bufferNum << 6; //32-Bit left shift
	int* r11 = globalVar + r0;
	int r12 = *(r11 + 0x2C);
	*(r11 + 0x38) = address;
	r0 = address + r12;
	*(r11 + 0x3C) = r0;
	*(r11 + 0x34) = address;
	*(r11 + 0x30) = r0;
}

//This is my refactoring, rewritten to make a bit more sense.
void* globalMemoryLocation; //preset
struct OSScreenBuffer {
	char unk[0x2B];
	int offset; //0x2C, preset
	int virtAddr; //0x30
	int realAddr; //0x34
	int realAddr2; //0x38
	int virtAddr2; //0x3C
}
void OSScreenSetBufferEx_refactored(int bufferNum, void* address) {
	OSScreenBuffer* buffer = globalMemoryLocation + (bufferNum << 6);
	buffer->virtAddr = address + buffer->offset;
	buffer->realAddr = address;
	buffer->realAddr2 = address;
	buffer->virtAddr2 = address + buffer->offset;
}