Author: Tom Kerrigan
Date: 01:27:46 01/15/02
Go up one level in this thread
On January 13, 2002 at 23:54:27, Eugene Nalimov wrote: >>>1. You know more about the program than the compiler. No bounds-checking >>>on "switch" type statements is necessary. >>What bounds checking or "switch type statements" are going on in a C program if >>you don't explicitly put them in? Right, sorry, I had misread the "on" as an "or." Anyway, if you (third person) think switch statements are slow, there's nobody forcing you to use them... >>>2. you know whether a value can be positive, negative, or both. The >>>compiler can't. >>Why does this matter? Just deal with 32 bits (or whatever your word size is) and >>call it good. >On 64-bit system you can avoid sign extension if you know that the value is >non-negative. Sometime you can achieve similar effect in C casting the value to >the unsigned, but code becomes uglier than even assembly one. I'm not sure where this would come up. With the RISC instruction sets I can remember, when you do loads of bytes, you can get sign extensions for free. >>The really strict calling conventions that you're thinking of here are no longer >>present in today's compilers. >Here you are only partially right... There are still cases where compiler have >to honour standard calling conventions. Yeah, but not in the cases where you would need code to be really fast. Unless you're doing API calls or something, which is a bummer, but doesn't need to happen in chess programs. >But Tom is partially right, too -- today's compilers are much better than ones >from 10 years ago. I am not talking about vectorizers, obviously major compiler >vendors started to look at them only recently, but for the control-heavy integer >code current compilers should produce reasonable code. I also think that what most people have been talking about--taking VC assembly output and tweaking it so it's faster--is cheating. I mean, is it really hand-coding when 90+% of your "hand code" comes from VC? And can you really say you're better at assembly programming than VC when if you wrote the assembly in a vacuum, it would be much slower than VC's output? -Tom
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