Threaded Mode | Linear Mode

J-F Garnier · (This post was last modified: 12-05-2022 03:34 PM by J-F Garnier.)

(12-05-2022 12:12 PM)Albert Chan Wrote: >20 def FNB(N) = IP(LOG2(N))+1
>X = 2^35
>X, FNB(X-1), FNB(X), FNB(X+1)
34359738368 36 36 36

For decimal machine, we may be hit with rounding errors. Any ideas ?

The same occurs with LOG10 when trying to get the exponent of a number:
X=10^11
LOG10(X);LOG10(X-1)
11 11
Fortunately, in this case we have the EXPONENT() function.

(12-05-2022 12:41 PM)Werner Wrote: Yes, the method I used in the VA12c challenge will return the correct answer in linear time for all arguments up to 2^35-1 (on a 42S) or to 2^WSIZE-1 on Free42 (WSIZE<45):

Code:

LBL D BINM @ set Binary mode, activates the BASE menu CLA ARCL ST X @ Alpha reg now contains X in binary CLX @ To replace X with the new value - my routine depended on that ALENG @ nr of bits EXITALL @ exit the BASE menu RTN

Sadly, that cannot be used on the 41. Don't know about the 71. On the 48, something similar may be done:

Code:

\<< BIN R\->B \->STR SIZE 3. - \>>

On the 71B or 75C w/ Math ROM, you can do:
DEF FNB(X)=LEN(BSTR$(X,2))
but I find it quite inelegant to resort to string conversion.

Edit: removed my other proposal. made a mistake in my tests :-(

J-F