+- HP Forums (https://www.hpmuseum.org/forum)
+-- Forum: HP Software Libraries (/forum-10.html)
+--- Forum: General Software Library (/forum-13.html)
+--- Thread: (42S) GCF (/thread-6533.html)
(42S) GCF - Gerald H - 07-10-2016 04:41 AM
Prompted by Eddie W Shore's
http://www.hpmuseum.org/forum/thread-6528.html
here's my short GCD programme.
The prog takes X & Y values from stack & returns GCD , or GCF if you wish, to stack level X.
Code:
0. { 16-Byte Prgm }
1. LBL “GCF”
2. LBL 00
3. MOD
4. LASTX
5. X<>Y
6. X≠0?
7. GTO 00
8. R↓
9. ABS
10. ENDRE: HP 42S: GCF - Werner - 07-10-2016 07:21 AM
Same as mine, except I have a "+" in step 8 (since you know X contains zero).
I also add Smallest Common Multiple:
*LBL "SCM"
RCL ST Y
RCL ST Y
XEQ 00
/
x
RTN
Cheers, Werner
RE: HP 42S: GCF - Guenter Schink - 07-10-2016 08:41 PM
Is this ABS necessary?
Günter
RE: HP 42S: GCF - Gerald H - 07-11-2016 04:26 AM
Yes, ABS is needed for some negative inputs, otherwise the GCD is returned as a negative which is surely not the GREATEST common factor.
RE: HP 42S: GCF - Gerald H - 07-11-2016 09:15 AM
(07-10-2016 07:21 AM)Werner Wrote: Same as mine, except I have a "+" in step 8 (since you know X contains zero).
I also add Smallest Common Multiple:
*LBL "SCM"
RCL ST Y
RCL ST Y
XEQ 00
/
x
RTN
Cheers, Werner
What does XEQ 00 do?
RE: HP 42S: GCF - Werner - 07-11-2016 10:01 AM
Look at your own code ;-)
it does GCF, I keep them both in 1 program.
Werner
RE: HP 42S: GCF - Dieter - 07-11-2016 06:58 PM
(07-10-2016 04:41 AM)Gerald H Wrote: here's my short GCD programme.
Fine – my fractions programs used virtually the same code, but with a final + instead of R↓ which works as a DROP here. ;-)
FTR, here is an alternate GCD routine with a slightly shorter and thus faster loop. It can be used if Z does not have to be preserved:
Code:
01 LBL 00
02 STO Z
03 MOD
04 X≠0?
05 GTO 00
06 +
07 ENDAnd finally a solution that returns both LCM and GCD (in Y resp. X):
Code:
01 LBL"LCMGCD"
02 STO T
03 X<>Y
04 ST* T
05 LBL 00
06 STO Z
07 MOD
08 X≠0?
09 GTO 00
10 +
11 ST/ Y
12 ENDThis is HP41 code. HP42s users may imagine an additional "ST" in the stack related commands. ;-)
Dieter
RE: HP 42S: GCF - Gerald H - 07-12-2016 04:46 AM
(07-11-2016 06:58 PM)Dieter Wrote:(07-10-2016 04:41 AM)Gerald H Wrote: here's my short GCD programme.
Fine – my fractions programs used virtually the same code, but with a final + instead of R↓ which works as a DROP here. ;-)
FTR, here is an alternate GCD routine with a slightly shorter and thus faster loop. It can be used if Z does not have to be preserved:
Code:
01 LBL 00
02 STO Z
03 MOD
04 X≠0?
05 GTO 00
06 +
07 END
And finally a solution that returns both LCM and GCD (in Y resp. X):
Code:
01 LBL"LCMGCD"
02 STO T
03 X<>Y
04 ST* T
05 LBL 00
06 STO Z
07 MOD
08 X≠0?
09 GTO 00
10 +
11 ST/ Y
12 END
This is HP41 code. HP42s users may imagine an additional "ST" in the stack related commands. ;-)
Dieter
I tried the first programme but for various inputs it returned 1.
RE: HP 42S: GCF - Gerald H - 07-12-2016 04:59 AM
Sorry, my error, I entered STO "Z" for STO ST Z.
Now functions correctly.