(42S) GCD

[Eddie W. Shore]

HP 42S: GCD (Greatest Common Divisor) by Euclid Division

Enter the two integers on the Y stack and X stack. Order doesn’t matter.

Code:

00 {42-Byte Prgm}
01 LBL “GCD”
02 X<Y?
03 X<>Y
04 STO 01  \\ store maximum in R01
05 X<>Y
06 STO 00  \\ store minimum in R00
07 LBL 00 \\ main loop
08 RCL 01
09 ENTER
10 RCL÷ 00
11 IP
12 RCL* 00
13 –
14 X=0?  \\ is max – IP(min/max)*min = 0?
15 GTO 01
16 X<>Y 
17 STO 01
18 X<>Y 
19 STO 00
20 GTO 00
21 LBL 01 \\ display GCD
22 RCL 00 
23 “GCD:”
24 ARCL ST X
25 AVIEW
26 END

Test: Find the GCD of 485 and 175.
485 [ENTER] 175 [XEQ] {GCD} Result: 5
Alternatively:
175 [ENTER] 485 [XEQ] {GCD} Result: 5