(11C) 100 virtual registers
03-18-2018, 12:04 AM
Post: #1
 Michael Zinn Member Posts: 56 Joined: Mar 2018
(11C) 100 virtual registers
Get 100 virtual registers instead of just 20!

These are STO and RCL commands to store a number between 0 and 99 in a virtual register numbered 0 to 99. I recommend using labels D and E because they are in the same columns as STO and RCL.

vRCL x
Recall a number from virtual register X. Notice how this affects the stack:

Before:
T: ?
Z: z
Y: y
X: Register number (0-99)

After:
T: z
Z: z
Y: y
X: Register content

y vSTO x
Stores Y in virtual register X. Unlike regular STO, this removes the value from the stack so if you need it again you'll have to vRCL it. This also destroys T:

Before:
T: ?
Z: z
Y: Data (0-99)
X: Register (0-99)

After:
T: Garbage
Z: z
Y: z
X: z

Only tested on the Android 11i simulator, but it should work on real devices (please comment if it doesn't):

Code:
LBL D 5 / STO I FRAC 10 * 10^x RCL (i) x><y / FRAC + 2 10^x / GSB 0 RCL (i) x><y / INT + GSB 0 * STO (i) R\/ RTN LBL 0 RCL I FRAC 10 * 2 + 10^x RTN LBL E 5 / STO I FRAC 10 * 2 + 10^x RCL (i) x><y / FRAC 2 10^x * INT RTN
03-18-2018, 04:23 PM
Post: #2
 Michael Zinn Member Posts: 56 Joined: Mar 2018
RE: (11C) 100 virtual registers
If you take into account that the program itself takes about 9 registers worth of storage away it is still worth it if numbers in the range 0-99 are enough for your program because you effectively gained 35 more registers (100 - 9*5 - 20).

The method would also work for differenty sized virtual register:

Code:
 Number of registers | Possible values --------------------+----------------                 200 | 0-9                 100 | 0-99 (default)                  60 | 0-999                  40 | 0-99999
03-18-2018, 06:29 PM
Post: #3
 Dieter Senior Member Posts: 2,397 Joined: Dec 2013
RE: (11C) 100 virtual registers
(03-18-2018 12:04 AM)michaelzinn Wrote:  Get 100 virtual registers instead of just 20!

I see you are rediscovering techniques from the Seventies. ;-) Storing multiple integers in a single data register soon became popular with the advent of the HP67/97 in 1976, as these were – as far as I know – the first HPs that offered indirect addressing.

There are even HP programs where you can see this method at work. Take a look at this moon phase program for the HP41. The initialization routine prestores numerous two-digit integers where each register holds three or five at a time.

By the way: instead of 2 [10^x] you better use [EEX] 2. That's faster and it's also safe on early HPs where 10^x is prone to roundoff errors (HP25: 8 [10^x] => 99999999,60). That's exactly why HP soon switched to 13-digit internal precision.

Dieter
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