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+--- Thread: INV DSZ in its natural habitat (/thread-17585.html)
INV DSZ in its natural habitat - Dave Britten - 10-15-2021 01:56 PM
Yesterday there was some question as to whether or not the INV DSZ (decrement and skip if not zero) instruction present on some TIs was at all useful. I maintain that it's useful in any situation where you decrement a counter and break out of the middle of a loop, rather than at the end of the loop body.
I put together a little example by way of a cumulative binomial distribution program. First, a BASIC version for the 71B that makes the algorithm a little easier to read:
Code:
0001 DESTROY ALL
0010 INPUT "N?";N
0020 INPUT "P?";P
0030 INPUT "X?";X
0040 T=0 @ R=0
0050 F=P/(1-P)
0060 K=X+1
0070 B=(1-P)^N
0080 T=T+B
0090 K=K-1 @ IF K=0 THEN GOTO 120 @ REM INV DSZ!
0100 B=B*(N-R)/(R+1)*F @ R=R+1
0110 GOTO 80
0120 PRINT TTo use it, run the program, enter the number of trials N, the probability of success in a single trial P, and the number of successful trials X. The program will show the cumulative lower tail binomial probability, i.e. probability of the number of successes being between 0 and X.
Note line 90, where the program decrements a counter, and breaks out of the middle of the loop (lines 80 to 110) when the counter reaches zero.
Now, here are printouts of both an HP 97 version, and a TI-59 version. On the HP version, you have to do something like using an extra LBL and GTO to invert the DSZ test behavior. On the TI-59, you can simply use INV DSZ directly.
To run either of these, store N in R01, P in R02, X in R03, and press A.
https://i.imgur.com/rxENjWN.jpg
Ignoring the fact that the TI program is about twice the size of the HP one
it's clear that this is a case where INV DSZ can be used to save a couple of steps, and make the program flow easier to read.
RE: INV DSZ in its natural habitat - BruceH - 10-15-2021 04:18 PM
I assume these two statements are used to implement the following types of loop (expressed in C syntax), in which case both have their place.
Code:
/* DSZ */
do {
...
} while (--x != 0)whereas
Code:
/* INV DSZ (or DSNZ) */
while (--x != 0) {
...
}RE: INV DSZ in its natural habitat - Dave Britten - 10-15-2021 04:24 PM
Kind of. It's more akin to this, at least in my example:
Code:
c = 10;
while (true) {
//do stuff
if (--c == 0) break;
//do more stuff
}RE: INV DSZ in its natural habitat - Ross Barnes - 10-16-2021 12:12 AM
Dave,
Someone at TI found INV DSZ useful since it was used in steps 28-29 of their Battleship program in the SR-56 Application Library book, p. 188.
Ross
RE: INV DSZ in its natural habitat - xerxes - 10-18-2021 06:38 PM
INV DSZ/ISZ can be usefull in some cases. Here a size optimized code for the TI-62 to calculate the factoral:
Code:
00 *
01 INV DSZ
02 R/S
03 RCL 0Usage example: 69 STO 0 RST R/S
RE: INV DSZ in its natural habitat - Dave Britten - 10-19-2021 06:54 PM
(10-18-2021 06:38 PM)xerxes Wrote: INV DSZ/ISZ can be usefull in some cases. Here a size optimized code for the TI-62 to calculate the factoral:
Code:
00 *
01 INV DSZ
02 R/S
03 RCL 0
Usage example: 69 STO 0 RST R/S
Nice, didn't realize the lower-end machines had it too. I wonder if it works on the TI-65.
RE: INV DSZ in its natural habitat - xerxes - 10-19-2021 09:03 PM
(10-19-2021 06:54 PM)Dave Britten Wrote: Nice, didn't realize the lower-end machines had it too. I wonder if it works on the TI-65.
INV DSZ is also present on the TI-65, but I'm not sure, if the code works on the TI-65 too, because it based on the circular program execution ability of the TI-62.