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Date: Tue, 4 Sep 2018 16:12:07 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Sandipan Das <sandipan@linux.ibm.com>
Cc: mpe@ellerman.id.au, paulus@samba.org, naveen.n.rao@linux.vnet.ibm.com,
 linuxppc-dev@lists.ozlabs.org, anton@samba.org, ravi.bangoria@linux.ibm.com
Subject: Re: [PATCH 3/6] powerpc sstep: Add cnttzw,
 cnttzd instruction emulation
Message-ID: <20180904211207.GO24439@gate.crashing.org>
References: <cover.1535609090.git.sandipan@linux.ibm.com>
 <f989c31bcf4bd8a80a50fa6899bcd239ed1bec69.1535609090.git.sandipan@linux.ibm.com>
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On Mon, Sep 03, 2018 at 08:49:35PM +0530, Sandipan Das wrote:
> +		case 538:	/* cnttzw */
> +			if (!cpu_has_feature(CPU_FTR_ARCH_300))
> +				return -1;
> +			val = (unsigned int) regs->gpr[rd];
> +			op->val = ( val ? __builtin_ctz(val) : 32 );
> +			goto logical_done;
> +#ifdef __powerpc64__
> +		case 570:	/* cnttzd */
> +			if (!cpu_has_feature(CPU_FTR_ARCH_300))
> +				return -1;
> +			val = regs->gpr[rd];
> +			op->val = ( val ? __builtin_ctzl(val) : 64 );
> +			goto logical_done;

__builtin_ctz(val) is undefined for val == 0.


Segher