Optimized kernel builds: the straight dope [fp extensions]

[John Richard Moser]

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Krzysztof Lichota wrote:
> John Richard Moser napisał(a):
>> I've been told that using SSE (the SIMD floating point extension that
>> Intel developed) takes ~17 cycles to load an SSE register because it's
>> not standard IEEE 754 floats and thus has to be converted from the FPU
>> registers.  Also the SIMDs are all floating point, it makes no sense to
>> copy data back and forth like that; a MOV, MOVS, or MOVSB instruction
>> would be faster and more appropriate.
> 
> MMX instructions were integer operations. SSE introduced floating-point
> operations. SSE2 introduced integer operations on longer registers. See:
> http://en.wikipedia.org/wiki/Streaming_SIMD_Extensions.
> SIMD is just the name of generic type of instructions.
> 

Yes I know, I said SSE was a SIMD floating point extension; although I
guess I didn't know SSE2 had integer operations as well.

It doesn't change the fact that good old i286 movsb still works and is
more appropriate than fancy SSE instructions made for heavy special-use
scenarios

> 	Krzysztof Lichota
> 
> 

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