From: Clemens Ladisch <clemens@ladisch.de>
To: Ben Greear <greearb@candelatech.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Is __ffs64 supposed to be zero based?
Date: Wed, 06 Nov 2013 12:52:43 +0100 [thread overview]
Message-ID: <527A2D8B.6030901@ladisch.de> (raw)
In-Reply-To: <5279ECA8.5080701@candelatech.com>
Ben Greear wrote:
> Similarly named methods elsewhere seem to indicate it is supposed to be
> ones-based counting (ie, bit (1<<0) would be considred 'bit 1'.
ffs() is defined to use one-based counting:
<http://pubs.opengroup.org/onlinepubs/9699919799/functions/ffs.html>
__ffs() uses zero-based counting. On gcc, it's likely to be implemented
with__builtin_ctz*(), whose documentation says:
| Returns the number of trailing 0-bits in x, starting at the least
| significant bit position.
Regards,
Clemens
next prev parent reply other threads:[~2013-11-06 11:52 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-06 7:15 Is __ffs64 supposed to be zero based? Ben Greear
2013-11-06 11:52 ` Clemens Ladisch [this message]
2013-11-06 17:17 ` Ben Greear
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