The Museum of HP Calculators

# Prime? for the HP 42s

This program was written by Wanda Louise & BabyNous and is used here by permission.

This program is supplied without representation or warranty of any kind. The author and The Museum of HP Calculators therefore assume no responsibility and shall have no liability, consequential or otherwise, of any kind arising from the use of this program material or any part thereof.

## Overview

The Program assumes that there is already a Real Matrix, of any Dimensions, already in Memory called: Prime.

Input: X: Real Number

Running Output: LUFRN: > CD
Where:
LUFRN is the Lowest UnFactored Real Number
CD is the Countdown (SQRT(Current Real) - current factor)

Terminal Output:
X: [ 1x? Matrix ]
1:1= Original Real
1:->= Prime Factors

## The Program

```LINE    KEYS
00  { 252-Byte Prgm }
01    LBL "Prm?"
02     STO "CREAL"
03     SQRT
04     STO "SQRTCR"
05     2
06     STO "CFACT"
07     1
08     STO "SZPRIME"
09     1
10     DIM "Prime"
11     INDEX "Prime"
12     STOIJ
13     RCL "CREAL"
14     STOEL

15    LBL a
16     CLA
17     ARCL "CREAL"
18     ?": > "
19     RCL "SQRTCR"
20     ENTER
21     RCL "CFACT"
22     -
23     IP
24     ARCL ST X
25     AVIEW
26     RCL "SQRTCR"
27     RCL "CFACT"
28     X>Y?
29     GTO e
30     XEQ A
31     RCL "CFACT"
32     2
33     X=Y?
34     GTO 01
35     2
36     GTO 00

37    LBL 01
38     1

39    LBL 00
40     STO+ "CFACT"
41     GTO a

42    LBL e
43     RCL "SZPRIME"
44     1
45     X!=Y?
46     GTO c
47     "Prime!!!"
48     AVIEW
49     GTO J

50    LBL c
51     "Composite!!!"
52     AVIEW
53     RCL "CREAL"
54     1
55     X=Y?
56     GTO J
57     1
58     STO+ "SZPRIME"
59     RCL "SZPRIME"
60     DIM "Prime"
61     STOIJ
62     RCL "CREAL"
63     STOEL

64    LBL J
65     CLST
66     RCL "Prime"
67     CLV "SZPRIME"
68     CLV "CFACT"
69     CLV "CREAL"
70     CLV "SQRTCR"
71     STOP

72    LBL A
73     RCL "CREAL"
74     RCL "CFACT"
75     ÷
76     ENTER
77     FP
78     X!=Y?
79     GTO B
80     roll dn
81     STO "CREAL"
82     SQRT
83     STO "SQRTCR"
84     1
85     STO+ "SZPRIME"
86     RCL "SZPRIME"
87     DIM "Prime"
88     STOIJ
89     RCL "CFACT"
90     STOEL
91     XEQ A

92    LBL B
93     RTN
94     END
```

## Variables

```CREAL:   Current Real
SQRTCR:  SQRT(CREAL)
CFACT:   Current Factor
SZPRIME: Size of Prime
Prime:   Final Matrix
```