Prev: Inputs left floating at the very start
Next: Microcontroller USB interface chip
From: Nils on 7 May 2008 05:15
CBFalconer schrieb:
> Nils wrote:
>> tims next home schrieb:
>>
>>>>> x = "\00\02\01"[x];
>>>> You are insufficiently depraved.
>>>> x = x["0\02\01"];
>>>> works, and is perfectly valid C.
>>> Not when working on my team, it isn't:-)
>> How about x = 4>>x
>
> After seeing the weird solutions I have decided that I AM
> insufficiently depraved. These ridiculous solutions just never
> occur to me. Am I missing something in the humour line?

I use computed shifts on magic numbers in time-critical code to compress
small lookup-tables into a single integer and index via shifts. That
little trick works well if the talbe only has few indices and each
element contains few bits. If all information fits into a machine-word
you get a very cheap LUT.

It saved my a** more than once.

But I'm doing low-level graphic rendering functions and most of the
stuff I write is in assembler. Saving a memory-access on the TI C64x+
DSP may give a factor2 performance win.

I wouldn't like to see such code in a non-critical path as well.

Nils
From: Walter Banks on 7 May 2008 08:03


CBFalconer wrote:

> Nils wrote:
> > tims next home schrieb:
> >
> >>>> x = "\00\02\01"[x];
> >>>
> >>> You are insufficiently depraved.
> >>> x = x["0\02\01"];
> >>> works, and is perfectly valid C.
> >>
> >> Not when working on my team, it isn't:-)
> >
> > How about x = 4>>x
>
> After seeing the weird solutions I have decided that I AM
> insufficiently depraved. These ridiculous solutions just never
> occur to me. Am I missing something in the humour line?

ISA's have changed over the years. I was amazed at
algorithmic opportunities that came with the first
barrel shifter where shift by 1 and shift by x took the
same execution time.

Partially microcoded instruction sets that allow different
operations on different execution cycles in a pipelined
processor may be a nightmare to code but it only has
to be right once.

Regards

--
Walter Banks
Byte Craft Limited
Tel. (519) 888-6911
http://www.bytecraft.com
walter(a)bytecraft.com



First  |  Prev  | 
Pages: 1 2 3 4 5
Prev: Inputs left floating at the very start
Next: Microcontroller USB interface chip