EllipticEllipsis

A very brief introduction to OoT's actor scaling code

We would like to understand this snippet of assembly code from OoT 1.2, in which we change the second 3C to a 3B to make Link small for smAll dungeons shenanigans:

...
/* 00FF78 80021658 3C053C23 */  lui         $a1, (0x3C23D70A >> 16)
/* 00FF7C 8002165C 34A5D70A */  ori         $a1, $a1, (0x3C23D70A & 0xFFFF)
/* 00FF80 80021660 0C008572 */  jal         Actor_SetScale
/* 00FF84 80021664 02002025 */   move       $a0, $s0

Converting a MIPS decompilation project to ABI FPR names

What?

If you've worked on a Nintendo 64 project, you're probably used to the floating-point registers in MIPS assembly being numbered, in a rather random-looking way, as the even numbers from 0-30. Some seem to be used for returns, some for arguments, some for temps, but there doesn't seem to be any much logic to it. And indeed there isn't, especially for the temp registers:

f0,f2 are return values (like v0,v1)
f12,f14 are function arguments (like a0,a1,...)
The other even-numbered ones are temporary and saved registers
Odd-numbered ones show up occasionally if doubles are about

i	0x10000 / i
1	0x10000
2	0x8000
3	0x5555
4	0x4000
5	0x3333
6	0x2AAA
7	0x2492

	#!/bin/bash

	# with quotes
	while read line ; do grep -Fr "$line" asm/non_matchings/code ; done < <(find asm/non_matchings/code/z_sub_s/ -type f -exec basename {} .s \;) \| grep -v 'glabel' \| awk -F':\|\\s+' '/%lo/ { next } /%hi/ { type="hilo" } /jal/ { type="jal" } { filefunc=gensub(/.\/(.)\/(.*)\.s/,"\\1,\\2","g",$1) ; gsub(/%hi\(\|\)/,"") ; print filefunc","$NF","type } ' \| awk -F, 'BEGIN { printf "digraph {\ncompound=true;\n\n" } { arr[$1] = arr[$1]" \""$2"\"" ; print "\""$2"\" -> \""$3"\"" } END { print "" ; for (file in arr) { print "subgraph cluster_"file" {" ; print arr[file]";" ; printf " style = filled;\n label = \"%s\";\n}\n\n" , file } print "}" }'

	# without quotes
	# while read line ; do grep -Fr "$line" asm/non_matchings/code ; done < <(find asm/non_matchings/code/z_sub_s/ -type f -exec basename {} .s \;) \| grep -v 'glabel' \| awk -F':\|\\s+' '/%lo/ { next } /%hi/ { type="hilo" } /jal/ { type="jal" } { filefunc=gensub(/.\/(.)\/(.*)\.s/,"\\1,\\2","g",$1) ; gsub(/%hi\(\|\)/,"") ; print filefunc","$NF

	#include <stdio.h>
	#include <stdint.h>
	#include <math.h>
	#include <assert.h>

	typedef union {
	float f;
	int32_t h;
	} FloatHex;

	#!/usr/bin/env python3
	import argparse
	import dataclasses
	import struct
	import sys
	import typing

	@dataclasses.dataclass
	class StandardLimb:
	jointPosX: int

	#include <stdint.h>
	#include <stdio.h>

	#define ARRAY_COUNT(arr) (sizeof(arr) / sizeof(arr[0]))

	// Test values for 0.05f
	// float test_mult[] = {
	// 5.0e-06f * 10000.0f, 5.0e-05f * 1000.0f, 0.0005f * 100.0f, 0.005f * 10.0f, 0.05f * 1.0f,
	// 0.5f * 0.1f, 5.0f * 0.01f, 50.0f * 0.001f, 500.0f * 0.0001f,
	// };

	#!/usr/bin/env python3

	import argparse
	from typing import List
	import dataclasses # cursed


	@dataclasses.dataclass
	class Flag:
	mask: int