diff --git a/src/include/lib/lib_04840.h b/src/include/lib/lib_04840.h
index d4d390cf5..0e55f3f83 100644
--- a/src/include/lib/lib_04840.h
+++ b/src/include/lib/lib_04840.h
@@ -3,7 +3,6 @@
 #include <ultra64.h>
 #include "types.h"
 
-u32 func00004840(void);
 void func00004a24(f32 *matrix, u16 *arg1, f32 fovy, f32 arg3, f32 arg4, f32 arg5, f32 arg6);
 
 #endif
diff --git a/src/lib/lib_04840.c b/src/lib/lib_04840.c
index 1072a8f22..4956197c9 100644
--- a/src/lib/lib_04840.c
+++ b/src/lib/lib_04840.c
@@ -13,143 +13,41 @@
 #include "lib/lib_4a360.h"
 #include "types.h"
 
-const u32 var700524b0[] = {0x3c8efa35};
-const u32 var700524b4[] = {0x00000000};
-const u32 var700524b8[] = {0x00000000};
-const u32 var700524bc[] = {0x00000000};
+void guPerspectiveF(float mf[4][4], u16 *perspNorm, float fovy, float aspect, float near, float far, float scale)
+{
+	float cot;
+	int	i, j;
 
-GLOBAL_ASM(
-glabel func00004840
-/*     4840:	27bdffd0 */ 	addiu	$sp,$sp,-48
-/*     4844:	44867000 */ 	mtc1	$a2,$f14
-/*     4848:	afbf0014 */ 	sw	$ra,0x14($sp)
-/*     484c:	afa50034 */ 	sw	$a1,0x34($sp)
-/*     4850:	afa7003c */ 	sw	$a3,0x3c($sp)
-/*     4854:	afa50034 */ 	sw	$a1,0x34($sp)
-/*     4858:	afa40030 */ 	sw	$a0,0x30($sp)
-/*     485c:	0c012918 */ 	jal	guMtxIdentF
-/*     4860:	e7ae0038 */ 	swc1	$f14,0x38($sp)
-/*     4864:	3c017005 */ 	lui	$at,%hi(var700524b0)
-/*     4868:	c7ae0038 */ 	lwc1	$f14,0x38($sp)
-/*     486c:	c42424b0 */ 	lwc1	$f4,%lo(var700524b0)($at)
-/*     4870:	3c013f00 */ 	lui	$at,0x3f00
-/*     4874:	44813000 */ 	mtc1	$at,$f6
-/*     4878:	46047382 */ 	mul.s	$f14,$f14,$f4
-/*     487c:	00000000 */ 	nop
-/*     4880:	46067302 */ 	mul.s	$f12,$f14,$f6
-/*     4884:	0c0068f4 */ 	jal	cosf
-/*     4888:	e7ac001c */ 	swc1	$f12,0x1c($sp)
-/*     488c:	c7ac001c */ 	lwc1	$f12,0x1c($sp)
-/*     4890:	0c0068f7 */ 	jal	sinf
-/*     4894:	e7a00020 */ 	swc1	$f0,0x20($sp)
-/*     4898:	c7a80020 */ 	lwc1	$f8,0x20($sp)
-/*     489c:	c7aa003c */ 	lwc1	$f10,0x3c($sp)
-/*     48a0:	c7ac0040 */ 	lwc1	$f12,0x40($sp)
-/*     48a4:	46004083 */ 	div.s	$f2,$f8,$f0
-/*     48a8:	c7b00044 */ 	lwc1	$f16,0x44($sp)
-/*     48ac:	8fa60030 */ 	lw	$a2,0x30($sp)
-/*     48b0:	8fa70034 */ 	lw	$a3,0x34($sp)
-/*     48b4:	46106480 */ 	add.s	$f18,$f12,$f16
-/*     48b8:	3c01bf80 */ 	lui	$at,0xbf80
-/*     48bc:	44814000 */ 	mtc1	$at,$f8
-/*     48c0:	46106381 */ 	sub.s	$f14,$f12,$f16
-/*     48c4:	00002825 */ 	or	$a1,$zero,$zero
-/*     48c8:	e4c8002c */ 	swc1	$f8,0x2c($a2)
-/*     48cc:	44804000 */ 	mtc1	$zero,$f8
-/*     48d0:	24040004 */ 	addiu	$a0,$zero,0x4
-/*     48d4:	e4c8003c */ 	swc1	$f8,0x3c($a2)
-/*     48d8:	460e9183 */ 	div.s	$f6,$f18,$f14
-/*     48dc:	e4c20014 */ 	swc1	$f2,0x14($a2)
-/*     48e0:	460a1103 */ 	div.s	$f4,$f2,$f10
-/*     48e4:	e4c60028 */ 	swc1	$f6,0x28($a2)
-/*     48e8:	460c6280 */ 	add.s	$f10,$f12,$f12
-/*     48ec:	e4c40000 */ 	swc1	$f4,0x0($a2)
-/*     48f0:	46105102 */ 	mul.s	$f4,$f10,$f16
-/*     48f4:	460e2183 */ 	div.s	$f6,$f4,$f14
-/*     48f8:	e4c60038 */ 	swc1	$f6,0x38($a2)
-/*     48fc:	c7a00048 */ 	lwc1	$f0,0x48($sp)
-.L00004900:
-/*     4900:	00001825 */ 	or	$v1,$zero,$zero
-/*     4904:	00c01025 */ 	or	$v0,$a2,$zero
-/*     4908:	c44e0000 */ 	lwc1	$f14,0x0($v0)
-/*     490c:	24630001 */ 	addiu	$v1,$v1,0x1
-/*     4910:	46007402 */ 	mul.s	$f16,$f14,$f0
-/*     4914:	50640008 */ 	beql	$v1,$a0,.L00004938
-/*     4918:	24420004 */ 	addiu	$v0,$v0,0x4
-.L0000491c:
-/*     491c:	c44e0004 */ 	lwc1	$f14,0x4($v0)
-/*     4920:	24630001 */ 	addiu	$v1,$v1,0x1
-/*     4924:	e4500000 */ 	swc1	$f16,0x0($v0)
-/*     4928:	46007402 */ 	mul.s	$f16,$f14,$f0
-/*     492c:	1464fffb */ 	bne	$v1,$a0,.L0000491c
-/*     4930:	24420004 */ 	addiu	$v0,$v0,0x4
-/*     4934:	24420004 */ 	addiu	$v0,$v0,0x4
-.L00004938:
-/*     4938:	e450fffc */ 	swc1	$f16,-0x4($v0)
-/*     493c:	24a50001 */ 	addiu	$a1,$a1,0x1
-/*     4940:	14a4ffef */ 	bne	$a1,$a0,.L00004900
-/*     4944:	24c60010 */ 	addiu	$a2,$a2,0x10
-/*     4948:	10e00032 */ 	beqz	$a3,.L00004a14
-/*     494c:	3c014000 */ 	lui	$at,0x4000
-/*     4950:	44813000 */ 	mtc1	$at,$f6
-/*     4954:	340effff */ 	dli	$t6,0xffff
-/*     4958:	3c014800 */ 	lui	$at,0x4800
-/*     495c:	4606903e */ 	c.le.s	$f18,$f6
-/*     4960:	00000000 */ 	nop
-/*     4964:	45020004 */ 	bc1fl	.L00004978
-/*     4968:	44814000 */ 	mtc1	$at,$f8
-/*     496c:	10000029 */ 	b	.L00004a14
-/*     4970:	a4ee0000 */ 	sh	$t6,0x0($a3)
-/*     4974:	44814000 */ 	mtc1	$at,$f8
-.L00004978:
-/*     4978:	24180001 */ 	addiu	$t8,$zero,0x1
-/*     497c:	3c014f00 */ 	lui	$at,0x4f00
-/*     4980:	46124283 */ 	div.s	$f10,$f8,$f18
-/*     4984:	24080001 */ 	addiu	$t0,$zero,0x1
-/*     4988:	444ff800 */ 	cfc1	$t7,$31
-/*     498c:	44d8f800 */ 	ctc1	$t8,$31
-/*     4990:	00000000 */ 	nop
-/*     4994:	46005124 */ 	cvt.w.s	$f4,$f10
-/*     4998:	4458f800 */ 	cfc1	$t8,$31
-/*     499c:	00000000 */ 	nop
-/*     49a0:	33180078 */ 	andi	$t8,$t8,0x78
-/*     49a4:	53000013 */ 	beqzl	$t8,.L000049f4
-/*     49a8:	44182000 */ 	mfc1	$t8,$f4
-/*     49ac:	44812000 */ 	mtc1	$at,$f4
-/*     49b0:	24180001 */ 	addiu	$t8,$zero,0x1
-/*     49b4:	46045101 */ 	sub.s	$f4,$f10,$f4
-/*     49b8:	44d8f800 */ 	ctc1	$t8,$31
-/*     49bc:	00000000 */ 	nop
-/*     49c0:	46002124 */ 	cvt.w.s	$f4,$f4
-/*     49c4:	4458f800 */ 	cfc1	$t8,$31
-/*     49c8:	00000000 */ 	nop
-/*     49cc:	33180078 */ 	andi	$t8,$t8,0x78
-/*     49d0:	17000005 */ 	bnez	$t8,.L000049e8
-/*     49d4:	00000000 */ 	nop
-/*     49d8:	44182000 */ 	mfc1	$t8,$f4
-/*     49dc:	3c018000 */ 	lui	$at,0x8000
-/*     49e0:	10000007 */ 	b	.L00004a00
-/*     49e4:	0301c025 */ 	or	$t8,$t8,$at
-.L000049e8:
-/*     49e8:	10000005 */ 	b	.L00004a00
-/*     49ec:	2418ffff */ 	addiu	$t8,$zero,-1
-/*     49f0:	44182000 */ 	mfc1	$t8,$f4
-.L000049f4:
-/*     49f4:	00000000 */ 	nop
-/*     49f8:	0700fffb */ 	bltz	$t8,.L000049e8
-/*     49fc:	00000000 */ 	nop
-.L00004a00:
-/*     4a00:	44cff800 */ 	ctc1	$t7,$31
-/*     4a04:	3319ffff */ 	andi	$t9,$t8,0xffff
-/*     4a08:	1f200002 */ 	bgtz	$t9,.L00004a14
-/*     4a0c:	a4f80000 */ 	sh	$t8,0x0($a3)
-/*     4a10:	a4e80000 */ 	sh	$t0,0x0($a3)
-.L00004a14:
-/*     4a14:	8fbf0014 */ 	lw	$ra,0x14($sp)
-/*     4a18:	27bd0030 */ 	addiu	$sp,$sp,0x30
-/*     4a1c:	03e00008 */ 	jr	$ra
-/*     4a20:	00000000 */ 	nop
-);
+	guMtxIdentF(mf);
+
+	fovy *= 3.1415926f / 180.0f;
+	cot = cosf(fovy * 0.5f) / sinf(fovy * 0.5f);
+
+	mf[0][0] = cot / aspect;
+	mf[1][1] = cot;
+	mf[2][2] = (near + far) / (near - far);
+	mf[2][3] = -1;
+	mf[3][2] = (2.0f * near * far) / (near - far);
+	mf[3][3] = 0;
+
+	for (i = 0; i < 4; i++) {
+		for (j = 0; j < 4; j++) {
+			mf[i][j] *= scale;
+		}
+	}
+
+	if (perspNorm != (u16 *) NULL) {
+		if (near + far <= 2.0f) {
+			*perspNorm = (u16) 0xFFFF;
+		} else {
+			*perspNorm = (u16) ((2.0f * 65536.0f) / (near + far));
+
+			if (*perspNorm <= 0) {
+				*perspNorm = (u16) 0x0001;
+			}
+		}
+	}
+}
 
 GLOBAL_ASM(
 glabel func00004a24
@@ -166,7 +64,7 @@ glabel func00004a24
 /*     4a4c:	27a40028 */ 	addiu	$a0,$sp,0x28
 /*     4a50:	e7a40010 */ 	swc1	$f4,0x10($sp)
 /*     4a54:	e7a60014 */ 	swc1	$f6,0x14($sp)
-/*     4a58:	0c001210 */ 	jal	func00004840
+/*     4a58:	0c001210 */ 	jal	guPerspectiveF
 /*     4a5c:	e7a80018 */ 	swc1	$f8,0x18($sp)
 /*     4a60:	27a40028 */ 	addiu	$a0,$sp,0x28
 /*     4a64:	0c0128d8 */ 	jal	guMtxF2L
@@ -176,4 +74,4 @@ glabel func00004a24
 /*     4a74:	03e00008 */ 	jr	$ra
 /*     4a78:	00000000 */ 	nop
 /*     4a7c:	00000000 */ 	nop
-);
\ No newline at end of file
+);
diff --git a/src/lib/lib_09660.c b/src/lib/lib_09660.c
index 137598773..15e9b509b 100644
--- a/src/lib/lib_09660.c
+++ b/src/lib/lib_09660.c
@@ -1636,7 +1636,7 @@ glabel func0000ab78
 /*     abb0:	27a40110 */ 	addiu	$a0,$sp,0x110
 /*     abb4:	27a50046 */ 	addiu	$a1,$sp,0x46
 /*     abb8:	e7a60014 */ 	swc1	$f6,0x14($sp)
-/*     abbc:	0c001210 */ 	jal	func00004840
+/*     abbc:	0c001210 */ 	jal	guPerspectiveF
 /*     abc0:	e7a80018 */ 	swc1	$f8,0x18($sp)
 /*     abc4:	0fc2d5be */ 	jal	currentPlayerGetMatrix1740
 /*     abc8:	00000000 */ 	nop
@@ -1718,7 +1718,7 @@ glabel func0000aca4
 /*     ace8:	27a50086 */ 	addiu	$a1,$sp,0x86
 /*     acec:	e7a80018 */ 	swc1	$f8,0x18($sp)
 /*     acf0:	e7a40010 */ 	swc1	$f4,0x10($sp)
-/*     acf4:	0c001210 */ 	jal	func00004840
+/*     acf4:	0c001210 */ 	jal	guPerspectiveF
 /*     acf8:	e7a60014 */ 	swc1	$f6,0x14($sp)
 /*     acfc:	27a40044 */ 	addiu	$a0,$sp,0x44
 /*     ad00:	0c0128d8 */ 	jal	guMtxF2L
@@ -1817,7 +1817,7 @@ glabel func0000ad5c
 /*     ae64:	24a52874 */ 	addiu	$a1,$a1,%lo(var80092874)
 /*     ae68:	24842830 */ 	addiu	$a0,$a0,%lo(var80092830)
 /*     ae6c:	e7a80018 */ 	swc1	$f8,0x18($sp)
-/*     ae70:	0c001210 */ 	jal	func00004840
+/*     ae70:	0c001210 */ 	jal	guPerspectiveF
 /*     ae74:	e7a60014 */ 	swc1	$f6,0x14($sp)
 /*     ae78:	3c048009 */ 	lui	$a0,%hi(var80092830)
 /*     ae7c:	3c058009 */ 	lui	$a1,%hi(var80092870)
@@ -1943,7 +1943,7 @@ glabel func0000af00
 /*     b04c:	24a52874 */ 	addiu	$a1,$a1,%lo(var80092874)
 /*     b050:	24842830 */ 	addiu	$a0,$a0,%lo(var80092830)
 /*     b054:	e7a80018 */ 	swc1	$f8,0x18($sp)
-/*     b058:	0c001210 */ 	jal	func00004840
+/*     b058:	0c001210 */ 	jal	guPerspectiveF
 /*     b05c:	e7a60014 */ 	swc1	$f6,0x14($sp)
 /*     b060:	3c048009 */ 	lui	$a0,%hi(var80092830)
 /*     b064:	3c058009 */ 	lui	$a1,%hi(var80092870)
@@ -2004,7 +2004,7 @@ glabel func0000b0e8
 /*     b130:	8fa60084 */ 	lw	$a2,0x84($sp)
 /*     b134:	8fa70088 */ 	lw	$a3,0x88($sp)
 /*     b138:	e7a80018 */ 	swc1	$f8,0x18($sp)
-/*     b13c:	0c001210 */ 	jal	func00004840
+/*     b13c:	0c001210 */ 	jal	guPerspectiveF
 /*     b140:	e7a60014 */ 	swc1	$f6,0x14($sp)
 /*     b144:	27a40040 */ 	addiu	$a0,$sp,0x40
 /*     b148:	0c0128d8 */ 	jal	guMtxF2L