Hi Steve,
in the (contributed) code there is:
// handle negative shifts special
if (shifts<0) {
stptr--;
} else {
stptr-=shifts;
}
and later
if (shifts<0) {
shiftstep = loop*rpnstack->s[stptr];
} else {
shiftstep = rpnstack->s[stptr+loop];
}
cheers
tobi
Wednesday Steve Shipway wrote:
> So, I'm delving into the PREDICT operations in the RPN, and have found
> something unexpected.
>
>
>
> There are two ways of specifying the shift offsets - as a (positive) count
> of shifts and a list; or as a negative count and a base shift.
>
>
>
> CDEF:predict1=172800,86400,0,3,3600,x,PREDICT
>
> CDEF:predict2=86400,-3,3600,x,PREDICT
>
>
>
> My tests (using 1.4.trunk) indicate that the two above have identical
> behaviour. My question is, is this intended? In particular, when giving a
> negative shift count, should the resulting list of shifts be based at 0?
>
>
>
> Given this:
>
>
>
> CDEF:predict=s,-3,w,x,PREDICT
>
>
>
> I had expected to get shifts of s, 2s and 3s. Instead I get 0, s and 2s.
> Is this intentional, or a feature?
>
>
>
> As a corollary, it means that these two lines are also equal for ANY value
> of s
>
>
>
> CDEF:predict1=s,-1,3600,x,PREDICT
>
> CDEF:predict2=x,3600,TRENDNAN
>
>
>
> Thanks,
>
>
>
> Steve
>
>
>
>
>
> Steve Shipway
>
> University of Auckland
>
> UNIX Systems Design Team Lead
>
> [email protected]
>
> +64 (9) 3737 599 ext 86487
>
>
>
>
--
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
www.oetiker.ch [email protected] +41 62 775 9902
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