On Wed, Dec 13, 2006 at 11:02:48AM +0100, Zoltan Menyhart wrote:
> I like this code with the following slight modifications:
> - let's keep "m" as pointer to volatile
Why? What benefit is there to doing an ld4.acq instead of a plain ld4?
> - let's keep on using "__u32" types
Why be so ugly?
> - not sure we need "new"
Good idea.
> - return the old bit
I don't understand what you mean here.
> volatile __u32 *m = (volatile __u32 *)addr + (nr >> 5);
> __u32 bit = 1 << (nr & 31);
>
> __u32 old = *m;
> while (!(old & bit)) {
> __u32 prev = cmpxchg_acq(m, old, old | bit);
> CMPXCHG_BUGCHECK(m);
> if (prev == old)
> return 0;
> old = prev;
> }
> return 1;
>
> It compiles to:
>
> 0: and r15=31,r32
> 6: mov r14=1
> c: extr r32=r32,5,27;;
> 10: shladd r18=r32,2,r33;;
> 16: ld4.acq r16=[r18]
> 1c: shl r17=r14,r15;;
> 20: and r14=r17,r16;;
> 26: nop.m 0x0
> 2c: cmp4.eq p7,p6=0,r14
> 30: nop.b 0x0
> 36: nop.b 0x0
> 3c: (p06) br.cond.dpnt.few a0 <+0xa0>
> 40: nop.m 0x0
> 46: zxt4 r14=r16
> 4c: nop.b 0x0;;
> 50: mov.m ar.ccv=r14;;
> 56: nop.m 0x0
> 5c: or r14=r17,r16
> 60: nop.m 0x0;;
> 66: cmpxchg4.acq r14=[r18],r14,ar.ccv
> 6c: nop.i 0x0;;
> 70: cmp4.eq p7,p6=r14,r16
> 76: nop.f 0x0
> 7c: and r15=r17,r14
> 80: mov r16=r14
> 86: nop.f 0x0
> 8c: (p07) br.cond.dpnt.few b0 <+0xb0>;;
> 90: nop.m 0x0
> 96: cmp4.eq p7,p6=0,r15
> 9c: (p07) br.cond.dptk.few 40 <+0x40>
> a0: nop.m 0x0
> a6: mov r8=1
> ac: br.ret.sptk.many b0;;
> b0: nop.m 0x0
> b6: mov r8=r0
> bc: br.ret.sptk.many b0;;
>
> It seems to be o.k., thanks.
>
> Zolt?n Menyh?rt
>
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