Floating-point Opcodes - Revision history

WiRe: /* FPU Tricks */

2024-02-13T17:14:43Z

‎FPU Tricks

2022-09-08T17:10:59Z

2020-07-09T11:51:50Z

FPU trick added

2020-06-05T09:12:07Z

Added image to floorcaster

2020-06-05T09:02:52Z

2020-06-05T09:02:28Z

2020-06-05T08:56:47Z

2020-05-30T18:57:01Z

‎FPU Tricks

2020-05-30T18:31:51Z

‎FPU Tricks

2020-05-30T18:26:31Z

‎FPU Tricks

← Older revision		Revision as of 17:14, 13 February 2024
Line 274:		Line 274:

	== FPU Tricks ==		== FPU Tricks ==
		+
		+	=== Need a constant? ===
		+	If you need an integer constant for your FPU operation, also see: [[General_Coding_Tricks#Need_a_constant.3F]]

	=== Comparing 2 float numbers on the FPU ===		=== Comparing 2 float numbers on the FPU ===

@@ Line 144: / Line 144: @@
 *<code>fmul dword [bx+si]</code>
 With the "Rrrola" trick above, we have the row number to be 204 at maximum, but also the column can't be greater than 256. This results in a wrong aspect ratio, but it can almost completely be fixed with this two byte instruction (+ one byte for the <code>AAS</code> instruction) : 256 * 1,24 = 317,44 which is quite close to 320. If aspect ratio is of no meaning to the desired effect, this three bytes can be shaved off.
 === The "Tunnel" ===

@@ Line 275: / Line 275: @@
 jb inside
 </syntaxhighlight>
 === Simple Floor Casting ===

@@ Line 282: / Line 282: @@
 Here is the basic code for the effect as used in e.g. [https://www.pouet.net/prod.php?which=85681 Rush, by: Marquee Design].
 <syntaxhighlight lang="nasm">
 fninit
-fild word [bx-8]	        ; load y-value
+fild word [bx-8]	; load y-value
-fidiv word [viewheight]         ; scalingvlaue/height to plane
+fidiv word [viewheight] ; scalingvalue/height to plane
-fabs 				; abs(y)
+fabs 			; abs(y)
-fild word [bx-9]	        ; x abs(y)
+fild word [bx-9]        ; x abs(y)
-fdiv st1                        ; x/abs(y) abs(y)
+fdiv st1                ; x/abs(y) abs(y)
-fistp word [bx-4]		; store U (plane x) to ax
+fistp word [bx-4]       ; store U (plane x) to ax
-fidivr word [floorval]          ; 32767/abs(y)
+fidivr word [floorval]  ; 32767/abs(y)
-fist word [bx-6]		; store V (plane y) to cx
+fist word [bx-6]        ; store V (plane y) to cx
 </syntaxhighlight>

@@ Line 275: / Line 275: @@
 jb inside
 </syntaxhighlight>
 === Simple Floor Casting ===

@@ Line 278: / Line 278: @@
 === Simple Floor Casting ===
-Another classic effect that works well with the FPU is a simple Perspective Floor Caster. While this effect can also be achieved with just CPU code, using the FPU gives a bit finer control over things like camera height and other things.
+Another classic effect that works well with the FPU is a simple Perspective Floor Caster.
 Here is the basic code for the effect as used in e.g. [https://www.pouet.net/prod.php?which=85681 Rush, by: Marquee Design].
@@ Line 300: / Line 301: @@
 </syntaxhighlight>
-Needless to say, the code above is simplified and unoptimised or educational purposes, but can be optimised further using various tricks mentioned above and integrated easily into already existing FPU calculations for example to save space.
+Needless to say, the code above is simplified and unoptimised or educational purposes.

← Older revision		Revision as of 08:56, 5 June 2020
Line 275:		Line 275:
	jb inside		jb inside
	</syntaxhighlight>		</syntaxhighlight>
		+
		+
		+	=== Simple Floor Casting ===
		+	Another classic effect that works well with the FPU is a simple Perspective Floor Caster. While this effect can also be achieved with just CPU code, using the FPU gives a bit finer control over things like camera height and other things.
		+
		+	Here is the basic code for the effect as used in e.g. [https://www.pouet.net/prod.php?which=85681 Rush, by: Marquee Design].
		+
		+	<syntaxhighlight lang="nasm">
		+	fninit
		+	fild word [bx-8] ; load y-value
		+	fidiv word [viewheight] ; scalingvlaue/height to plane
		+	fabs ; abs(y)
		+	fild word [bx-9] ; x abs(y)
		+	fdiv st1 ; x/abs(y) abs(y)
		+	fistp word [bx-4] ; store U (plane x) to ax
		+	fidivr word [floorval] ; 32767/abs(y)
		+	fist word [bx-6] ; store V (plane y) to cx
		+	</syntaxhighlight>
		+
		+	The following constants are used in the above calculation:
		+	<syntaxhighlight lang="nasm">
		+	floorval dw 32767
		+	viewheight dw 10
		+	</syntaxhighlight>
		+
		+	Needless to say, the code above is simplified and unoptimised or educational purposes, but can be optimised further using various tricks mentioned above and integrated easily into already existing FPU calculations for example to save space.

@@ Line 257: / Line 257: @@
 == FPU Tricks ==
-'''Comparing 2 float numbers on the FPU'''
+=== Comparing 2 float numbers on the FPU ===
 Sometimes when doing fpu algebra, you need to compare 2 float numbers using the FPU (for example when calculating an intersection between a point and an object).

← Older revision		Revision as of 18:26, 30 May 2020
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	'''Comparing 2 float numbers on the FPU'''		'''Comparing 2 float numbers on the FPU'''
		+
	Sometimes when doing fpu algebra, you need to compare 2 float numbers using the FPU (for example when calculating an intersection between a point and an object).		Sometimes when doing fpu algebra, you need to compare 2 float numbers using the FPU (for example when calculating an intersection between a point and an object).