From 24a293620f9b5c077147fae19129f4ff6dc8ee33 Mon Sep 17 00:00:00 2001
From: Ryan Dwyer <ryandwyer1@gmail.com>
Date: Thu, 7 Oct 2021 22:30:35 +1000
Subject: [PATCH] Disassemble rng functions

---
 src/lib/rng.c | 69 -----------------------------------------------
 src/lib/rng.s | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+), 69 deletions(-)
 delete mode 100644 src/lib/rng.c
 create mode 100644 src/lib/rng.s

diff --git a/src/lib/rng.c b/src/lib/rng.c
deleted file mode 100644
index ddd9e66c7..000000000
--- a/src/lib/rng.c
+++ /dev/null
@@ -1,69 +0,0 @@
-#include <ultra64.h>
-#include "constants.h"
-#include "bss.h"
-#include "lib/rng.h"
-#include "lib/lib_2fa00.h"
-#include "data.h"
-#include "types.h"
-
-u64 g_RngSeed = 0xab8d9f7781280783;
-
-GLOBAL_ASM(
-glabel random
-/*    12dc0:	3c048006 */ 	lui	$a0,%hi(g_RngSeed)
-/*    12dc4:	dc84ee00 */ 	ld	$a0,%lo(g_RngSeed)($a0)
-/*    12dc8:	3c018006 */ 	lui	$at,%hi(g_RngSeed)
-/*    12dcc:	000437fc */ 	dsll32	$a2,$a0,0x1f
-/*    12dd0:	00042ff8 */ 	dsll	$a1,$a0,0x1f
-/*    12dd4:	000637fa */ 	dsrl	$a2,$a2,0x1f
-/*    12dd8:	0005283e */ 	dsrl32	$a1,$a1,0x0
-/*    12ddc:	0004233c */ 	dsll32	$a0,$a0,0xc
-/*    12de0:	00c53025 */ 	or	$a2,$a2,$a1
-/*    12de4:	0004203e */ 	dsrl32	$a0,$a0,0x0
-/*    12de8:	00c43026 */ 	xor	$a2,$a2,$a0
-/*    12dec:	0006253a */ 	dsrl	$a0,$a2,0x14
-/*    12df0:	30840fff */ 	andi	$a0,$a0,0xfff
-/*    12df4:	00862026 */ 	xor	$a0,$a0,$a2
-/*    12df8:	0004103c */ 	dsll32	$v0,$a0,0x0
-/*    12dfc:	fc24ee00 */ 	sd	$a0,%lo(g_RngSeed)($at)
-/*    12e00:	03e00008 */ 	jr	$ra
-/*    12e04:	0002103f */ 	dsra32	$v0,$v0,0x0
-);
-
-// Commented because ld isn't happy with bitshifting a u64.
-//u32 random(void)
-//{
-//	g_RngSeed = ((g_RngSeed << 63) >> 31 | (g_RngSeed << 31) >> 32) ^ (g_RngSeed << 44) >> 32;
-//	g_RngSeed = g_RngSeed >> 20 & 0xfff ^ g_RngSeed;
-//
-//	return g_RngSeed;
-//}
-
-GLOBAL_ASM(
-glabel rngSetSeed
-/*    12e08:	64840001 */ 	daddiu	$a0,$a0,0x1
-/*    12e0c:	3c018006 */ 	lui	$at,%hi(g_RngSeed)
-/*    12e10:	fc24ee00 */ 	sd	$a0,%lo(g_RngSeed)($at)
-/*    12e14:	03e00008 */ 	jr	$ra
-/*    12e18:	24040000 */ 	addiu	$a0,$zero,0x0
-);
-
-GLOBAL_ASM(
-glabel rngRotateSeed
-/*    12e1c:	dc870000 */ 	ld	$a3,0x0($a0)
-/*    12e20:	000737fc */ 	dsll32	$a2,$a3,0x1f
-/*    12e24:	00072ff8 */ 	dsll	$a1,$a3,0x1f
-/*    12e28:	000637fa */ 	dsrl	$a2,$a2,0x1f
-/*    12e2c:	0005283e */ 	dsrl32	$a1,$a1,0x0
-/*    12e30:	00073b3c */ 	dsll32	$a3,$a3,0xc
-/*    12e34:	00c53025 */ 	or	$a2,$a2,$a1
-/*    12e38:	0007383e */ 	dsrl32	$a3,$a3,0x0
-/*    12e3c:	00c73026 */ 	xor	$a2,$a2,$a3
-/*    12e40:	00063d3a */ 	dsrl	$a3,$a2,0x14
-/*    12e44:	30e70fff */ 	andi	$a3,$a3,0xfff
-/*    12e48:	00e63826 */ 	xor	$a3,$a3,$a2
-/*    12e4c:	0007103c */ 	dsll32	$v0,$a3,0x0
-/*    12e50:	fc870000 */ 	sd	$a3,0x0($a0)
-/*    12e54:	03e00008 */ 	jr	$ra
-/*    12e58:	0002103f */ 	dsra32	$v0,$v0,0x0
-);
diff --git a/src/lib/rng.s b/src/lib/rng.s
new file mode 100644
index 000000000..c94a82a22
--- /dev/null
+++ b/src/lib/rng.s
@@ -0,0 +1,74 @@
+#include "macros.inc"
+.set noat
+.set noreorder
+.set gp=64
+
+.data
+
+glabel g_RngSeed
+.dword 0xab8d9f7781280783
+
+.text
+
+/**
+ * u32 random(void)
+ *
+ * Generate a random number between 0 and 4294967295.
+ */
+glabel random
+	lui     $a0, %hi(g_RngSeed)
+	ld      $a0, %lo(g_RngSeed)($a0)
+	lui     $at, %hi(g_RngSeed)
+	dsll32  $a2, $a0, 31
+	dsll    $a1, $a0, 31
+	dsrl    $a2, $a2, 31
+	dsrl32  $a1, $a1, 0
+	dsll32  $a0, $a0, 12
+	or      $a2, $a2, $a1
+	dsrl32  $a0, $a0, 0
+	xor     $a2, $a2, $a0
+	dsrl    $a0, $a2, 20
+	andi    $a0, $a0, 0xfff
+	xor     $a0, $a0, $a2
+	dsll32  $v0, $a0, 0
+	sd      $a0, %lo(g_RngSeed)($at)
+	jr      $ra
+	dsra32  $v0, $v0, 0
+
+/**
+ * void rngSetSeed(u32 seed)
+ *
+ * Set the given seed as the RNG seed. Add 1 to make sure it isn't 0.
+ */
+glabel rngSetSeed
+	daddiu  $a0, $a0, 1
+	lui     $at, %hi(g_RngSeed)
+	sd      $a0, %lo(g_RngSeed)($at)
+	jr      $ra
+	li      $a0, 0
+
+/**
+ * u32 rngRotateSeed(u64 *value);
+ *
+ * Rotate the given seed using the same algorithm as random().
+ *
+ * Store the new 64-bit seed at the pointed address and return the same seed
+ * cast as a u32.
+ */
+glabel rngRotateSeed
+	ld      $a3, 0($a0)
+	dsll32  $a2, $a3, 31
+	dsll    $a1, $a3, 31
+	dsrl    $a2, $a2, 31
+	dsrl32  $a1, $a1, 0
+	dsll32  $a3, $a3, 12
+	or      $a2, $a2, $a1
+	dsrl32  $a3, $a3, 0
+	xor     $a2, $a2, $a3
+	dsrl    $a3, $a2, 20
+	andi    $a3, $a3, 0xfff
+	xor     $a3, $a3, $a2
+	dsll32  $v0, $a3, 0
+	sd      $a3, 0($a0)
+	jr      $ra
+	dsra32  $v0, $v0, 0