[arm] __arch__swab32.

["Paweł Sikora" <pluto@pld-linux.org>]

This function reverses the bytes in a word.
The method was discovered in 1986 following a competition between
ARM programmers. It requires just 4 instructions and 1 work register.

unsigned long reverse(unsigned long v)
{
 unsigned long t;
 t = v ^ ((v << 16) | (v >> 16)); // EOR r1,r0,r0,ROR #16     [*]
 t &= ~0xff0000;    // BIC r1,r1,#&ff0000
 v = (v << 24) | (v >> 8);  // MOV r0,r0,ROR #8
 return v ^ (t >> 8);   // EOR r0,r0,r1,LSR #8
}

Could we use the asm. optimized version instead of the generic ___swab32?

[*] http://gcc.gnu.org/PR18560

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                           #define say(x) lie(x)