Re: [9fans] circular fonctions: precision?

[Bakul Shah <bakul@bitblocks.com>]

On Oct 3, 2011, at 7:46 AM, erik quanstrom <quanstro@quanstro.net> wrote:

>> On Oct 3, 2011, at 4:41 AM, tlaronde@polynum.com wrote: >>
>>> But to come back to programming, when calculus is the crux, the more
>>> common/known even new!  programming languages are not great tools,
>>> and "portability" i.e.  proved accuracy of the implementation for a
>>> wide range of hardware/software is fuzzy.  And it's amazing to see
>>> how one can rapidly face errors even with very basic computations.
>>> And even with integer arithmetic, not much help is guaranteed by
>>> languages.
>>> 
>> Integer & rational arithmetic is guaranteed in Scheme and some other
>> languages.  In an R5RS compliant Scheme implementation you have for
>> example (/ 5 7) => 5/7.  (If only people get over their irrational
>> fear of prefix syntax they would discover a great little language in
>> Scheme.) But most prog.  languages do not specify minimal required
>> accuracy on standard floating pt.  functions.  May be because most
>> language hackers are not numerical analysts!
> 
> i think you've got it there.  how do i stuff 5/7 in a 32-bit ethernet register?
> if you're close to the h/w, it's probablly just confusing to fight it.

Ethernet ctlrs have FP registers these days? Wow! It is just a different fight. Scheme has conversion functions + macros to do what you want. Also note that most people do not work as closely to h/w as perhaps you or I do. And of course, you don't have to use just one language.

Funny you mention h/w. I have used scheme in the past for h/w testing as well as for generating code for a custom network processor. This NP had a 512 bit barrel shifter (could hold an entire 64 byte pkt and we could poke at any bitfield upto 32 bits in length). In my test library a 'shift' was (+ (quotient 512-bit-reg 2^32) new-32-bit-value)). Could've done in C but this was more fun and far fewer lines of code and far quicker to develop! I could represent an entire test pkt as a single number and shift into the barrelshifter etc. No need to worry about grotty indexing or off by 1 errors!