HP 12C decimal hexadecimal conversion

DEC -> HEX:
  Input integer 16-255
  Result format is nibble.nibble
                   [0-15].[00-15]
  e.g. 10.15 is AF
       12.05 is C5
  * Integers less than 16 are treated as hex

HEX -> DEC:
    Input format is nibble.nibble
                    [0-15].[00-15]
    e.g. enter 14.13 for ED
                1.11 for 1B
    Result is an integer

Side Effects: Z and T are clobbered

Program
-------
; Branch to DEC->HEX if 16 <= input value
; Otherwise continue to HEX->DEC
; Leaves 16 on the stack
01 16
03 <=
04 GTO 19

; HEX->DEC
; Stack: X:16 Y:[INPUT]
05 ROLL
06 DUP
07 INTG
08 16
10 *
11 SWAP
12 FRAC
13 100
16 *
17 +
18 GTO 00

; DEC->HEX
; Stack: X:16 Y:[INPUT]
19 /
20 DUP
21 INTG
22 SWAP
23 FRAC
24 .16
27 *
28 +
29 GTO 00

---------------------------------------------

This version clobbers financial registers
but restores Z and T on the stack

Program
-------
; Save the stack Z and T
01 ROLL
02 ROLL
03 STO PV
04 ROLL
05 STO FV
06 ROLL

; Branch to DEC->HEX if 16 <= input value
; Otherwise continue to HEX->DEC
; Leaves 16 on the stack
07 16
09 <=
10 GTO 25


; HEX->DEC
; Stack: X:16 Y:[INPUT]
11 ROLL
12 DUP
13 INTG
14 16
16 *
17 SWAP
18 FRAC
19 100
22 *
23 +
24 GTO 35

; DEC->HEX
; Stack: X:16 Y:[INPUT]
25 /
26 DUP
27 INTG
28 SWAP
29 FRAC
30 .16
33 *
34 +

; Restore the stack
35 RCL FV
36 RCL PV
37 ROLL
38 ROLL
; Optional you may want to clear
; financial registers
39 GTO 00