Re: [PATCH] x86: do not expose CONFIG_BSWAP to userspace

From: Ben Pfaff
Date: Wed Jan 28 2009 - 18:02:58 EST

Harvey Harrison <harvey.harrison@xxxxxxxxx> 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

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