linux-kernel - Re: [PATCH] x86: do not expose CONFIG

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Date:	Wed, 28 Jan 2009 15:04:07 -0800
From:	Ben Pfaff <blp@...stanford.edu>
To:	linux-kernel@...r.kernel.org
Subject:  Re: [PATCH] x86: do not expose CONFIG_BSWAP to userspace

Harvey Harrison <harvey.harrison@...il.com> writes:

> Is there a byteswap builtin in gcc?  At least AVR32
> seems to use it, but perhaps it's not generally exposed...perhaps we
> could ask the gcc-folk?

Yes, GCC has byteswap builtins on x86 documented as follows:

 -- Built-in Function: int32_t __builtin_bswap32 (int32_t x)
     Returns X with the order of the bytes reversed; for example,
     `0xaabbccdd' becomes `0xddccbbaa'.  Byte here always means exactly
     8 bits.

 -- Built-in Function: int64_t __builtin_bswap64 (int64_t x)
     Similar to `__builtin_bswap32', except the argument and return
     types are 64-bit.

These were only added as of GCC 4.3 though.
-- 
Ben Pfaff 
http://benpfaff.org

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