FPC4GBA vs GPC4GBA :P

**dmantione** · 17-01-2006, 08:28 PM

The save into r8 should be a proper save, unless the compiler expects you to save r8 which you destroy. Hmmm.... I'm going need take a look at the code myself, you can send me the code if you wish so... If no time tomorrow though.

In the meantime, please compare a version with the "mod" defined as function in the program and when it is in the RTL. Can you see differences?

**Legolas** · 17-01-2006, 10:31 PM

Originally Posted by dmantione

The save into r8 should be a proper save, unless the compiler expects you to save r8 which you destroy. Hmmm.... I'm going need take a look at the code myself, you can send me the code if you wish so... If no time tomorrow though.

In the meantime, please compare a version with the "mod" defined as function in the program and when it is in the RTL. Can you see differences?

Looking at the compiler generated .s files I can find some small differences, mainly dues to different implementation, I think.
This comes from function version:

Code:

# &#91;41&#93; c &#58;= modulus&#40;&#40;i * j&#41;, 31&#41;;
	mov	r1,#31
	# Register r0 allocated
	mov	r0,r4
	# Register r2 allocated
	mov	r2,r5
	# Register r0,r2 released
	# Register r0 allocated
	mul	r0,r2,r0
	# Register r2,r3,r12,r13,r14,r15 allocated
	bl	P$FILLSCREEN_FPC_MODULUS$LONGINT$LONGINT$$LONGINT
	# Register r1,r2,r3,r12,r13,r14,r15,r0 released
	mov	r6,r0
	# Register r0 allocated
# &#91;43&#93; VideoBuffer&#91;j + 240 * i&#93; &#58;= c;

and this other one comes from rtl version:

Code:

# &#91;39&#93; c &#58;= &#40;i * j&#41; mod 31;
	mov	r0,r4
	# Register r2 allocated
	mov	r2,r5
	# Register r0,r2 released
	# Register r1 allocated
	mul	r1,r2,r0
	# Register r0 allocated
	mov	r0,#31
	# Register r2,r3,r12,r13,r14,r15 allocated
	bl	fpc_mod_longint
	# Register r1,r2,r3,r12,r13,r14,r15,r0 released
	mov	r6,r0
	# Register r0 allocated
# &#91;43&#93; VideoBuffer&#91;j + 240 * i&#93; &#58;= c;

This is the 'modulus' function:

Code:

.globl	P$FILLSCREEN_FPC_MODULUS$LONGINT$LONGINT$$LONGINT
P$FILLSCREEN_FPC_MODULUS$LONGINT$LONGINT$$LONGINT&#58;
# Temps allocated between r11-44 and r11-44
	# Register r13,r11,r12 allocated
	mov	r12,r13
	stmfd	r13!,&#123;r11,r12,r14,r15&#125;
	sub	r11,r12,#4
	# Register r12 released
	sub	r13,r13,#44
# Var number located in register
# Var denom located in register
# Temp -44,4 allocated
# Var $result located at r11-44
	# Register r0,r1,r2,r3,r12,r13,r14,r15 allocated
# &#91;27&#93; swi #0x060000
	swi	#393216
# &#91;28&#93; mov r0, r1
	mov	r0,r1
	# Register r0,r1,r2,r3,r12,r13,r14,r15 released
# Temp -44,4 released
	ldmea	r11,&#123;r11,r13,r15&#125;
	# Register r0 released
.Le0&#58;
	.size	P$FILLSCREEN_FPC_MODULUS$LONGINT$LONGINT$$LONGINT, .Le0 - 
P$FILLSCREEN_FPC_MODULUS$LONGINT$LONGINT$$LONGINT

It does some "strange" things with r11, r12 and r13 that i can't understand (maybe something related to stack, given that r13 is the stack pointer?).

I can zip all rtl sources and this small example and send it to your mailbox, if you want.

**dmantione** · 17-01-2006, 11:01 PM

I think I see the problem! :twisted:

Function:

Code:

   mul   r0,r2,r0  # In other words&#58; the function stores i*j in r0
   bl   P$FILLSCREEN_FPC_MODULUS$LONGINT$LONGINT$$LONGINT

RTL:

Code:

  mov r0,#31  # In other words, the rtl stores #31 in r0
  bl   fpc_mod_longint

In other words, the parameters are reversed!!

Try this:

[pascal]
function fpc_mod_longint(n,z: longint):longint; compilerproc; assembler; [public, alias: 'FPC_MOD_LONGINT'];
asm
; Reverse the parameters!
mov r2,r0
mov r0,r1
mov r1,r2
; Do software interrupt.
swi #0x060000
mov r0, r1
end['r0','r1','r2','r3'];
[/pascal]

**Legolas** · 17-01-2006, 11:10 PM

YAY!!! It works!!! :mrgreen: :mrgreen: :mrgreen:
You, THE genius! :clap:

In other words, I don't understand ASM :lol:

Thanks alot, Daniel. I should offer a beer to you ^_^

**savage** · 18-01-2006, 09:19 AM

So any screen shots or something to show working?

**Legolas** · 18-01-2006, 01:29 PM

Originally Posted by savage

So any screen shots or something to show working?

Oh, well... nothing so fun to show. I only have this screenshot:

The code is tacken from an example on Mr. Harbour's book. The interesting thing is that now fpc executable runs faster than the gcc one

BTW, I have found a nice trick for swapping two registers without involving a third one:

Code:

  eor r0, r0, r1
  eor r1, r1, r0
  eor r0, r0, r1

**Legolas** · 20-01-2006, 02:26 PM

Work goes on... I have discovered why the 2 registers for mod are swapped: in thumb mode it should be used SWI 6 (r0->number, r1->denom); in arm mode SWI 7 (r1->number, r0->denom). So, no need to swap registers... I only have mistaken SWI

ops:

BTW, now I have some problems with asm 'dialect' in fpc. Seems like it is not so much standard compliant. For example, it does not understand asm comments (@,

but pascal ones (//); labels should always start with .L; in some cases, asm code that works in gas is not understood by fpc:

Code:

mov 	r0, #0x4000006

generates an "invalid constant" error;

Code:

mov    r0, r0, lsl #0x10

generates an obscure "internal error 200501051"; elsewhere 'lsl' is an invalid opcode. My asm skills are near to 0, so probably I'm doing something wrong in the code. :?:

**dmantione** · 21-01-2006, 01:24 PM

This is really a question for Florian. The second one is definately a bug, so feel free to submit one. The first one I don't know, perhaps try to use Pascal syntax, $ instead of ox? Anyway, please ask Florian what to do here.

**Legolas** · 25-01-2006, 02:45 PM

Originally Posted by Legolas

Code:

mov 	r0, #0x4000006

generates an "invalid constant" error;

Oh, I respond by myself: ARM does not allow to load any value in a register, but only (8 bit value) << (x*2) values, according with this faq.
About the other question, I have submitted a bug report, so I'm waiting for a fix.

In the meanwhile I'm trying to make some nicer-to-look demos, hoping that this can attract more people joining fpc4gba project...

**dmantione** · 26-01-2006, 08:27 AM

Just a suggestion, you're posting news on your own site. There is nothing wrong with that, but the FPC4GBA url is a little more published. It is there where you need to show the world your progress.