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- Subject: Re: LuaJIT with vectors
- From: David Kastrup <dak@...>
- Date: Thu, 18 Nov 2010 14:29:07 +0100
Alex Queiroz <firstname.lastname@example.org> writes:
> On Thu, Nov 18, 2010 at 11:17 AM, David Kastrup <email@example.com> wrote:
>> Alex Queiroz <firstname.lastname@example.org> writes:
>>> Sometimes I wonder how plain Lua can be so fast sticking only to
>>> standard ANSI C. That's an achievement. For instance, the VM dispatch
>>> uses the C switch statement, which is known to be slow.
>> Huh? Why would it be "known to be slow"? Have you taken a look at the
>> kind of code it generates?
> The standards-compliant switch statement must emit code to check
> interval range.
Not if the data type is covered exhaustively.
> This code kills the CPU predictor and causes severe pipeline flushing.
I have yet to see an alternative that can predict the opcodes.