Asm Function

[GnoStiC]

first of all, sorry if this is already discussed before..

this is C version:

/* BTST.L Dn,Dn */
unsigned long REGPARAM2 CPUFUNC(op_0100_0)(uae_u32 opcode, struct regstruct *regs)
{
	uae_u32 srcreg = ((opcode >> 9) & 7);
	uae_u32 dstreg = opcode & 7;
{{	uae_s32 src = m68k_dreg (regs, srcreg);
{	uae_s32 dst = m68k_dreg (regs, dstreg);
	src &= 31;
	SET_ZFLG (&regs->ccrflags, 1 ^ ((dst >> src) & 1));
}}}	m68k_incpc (regs, 2);
return 4 * 256;
}

let's say i want to rewrite this in asm:

unsigned long REGPARAM2 CPUFUNC(op_0100_0)(uae_u32 opcode, struct regstruct *regs)
{
// r0 = opcode
// r1 = *regs
asm volatile (
"mov	 r3, r0,lsr#9		\n\t"; r3 = r0 >> 9
"and	 r3, r3, #7			 \n\t"; r3 & 7 (r3 = srcreg)
"and	 r0, r0, #7			 \n\t"; r0 & 7 (r0 = dstreg)

"ldr	 r2, [r1,r3,lsl#2]	  \n\t"; r2 = (regs, srcreg) (r2 = src)
"ldr	 r3, [r1,r0,lsl#2]	  \n\t"; r3 = (regs, dstreg) (r3 = dst)
"and	 r2, r2, #0x1F		  \n\t"; r2 & 31		

"ldr	 r0, [r1,#0x40]		 \n\t"; r0 = regs->crrflgs 
"mov	 r3, r3,asr r2		  \n\t"; r3 >> r2
"and	 r3, r3, #1			 \n\t"; r3 & 1
...

now,
can i write

"mov	 r3, opcode,lsr#9		\n\t"; r3 = r0 >> 9

instead of

"mov	 r3, r0,lsr#9		\n\t"; r3 = r0 >> 9

and is it safe to assume that r0 (and r1) are always likely to be cloberred in a function call, so i don't need to put them on my "regs to be clobberred" list?
&
can i set a global clobber list?

 

[notaz]

why don't you put that into separate .S file? That way you would be 100% sure that compiler won't get in your way. That is, of course, only valid if you are not going use C later in that function.