For and While in Studio 5000 Ladder?

[joseph_e2]

...Also, a value of -32768 in Element causes an underflow, if that causes a trap and/or PLC fault you might need to guard against it.

A 16-bit signed integer can handle -32768 up to 32767.

 

[TheWaterboy]

ASF's code with the minor adjustment to the location of the JMP works perfectly and it's pretty fast. Not quite as fast as the ST but close enough. I combined it with the rest of the logic needed, made an AOI and it works great.

I just wish I could pull the description field from a Logix PLC tag from within PLC logic. That would be the cherry on top - but alas that can't yet be done.

Thanks to all for the assist.

 

[drbitboy]

A 16-bit signed integer can handle -32768 up to 32767.

Yes, and subtracting 1 from -32768 would cause and overflow, and any 16-bit signed integer with a value of 1 in alarm bit 15 will eventually result in subtracting 1 from -32768.

Update: Actually, these appear to be DINTs, but they still have the same problem if any bit 31 values are 1.

 

[drbitboy]

ASF's code with the minor adjustment to the location of the JMP works perfectly and it's pretty fast. Not quite as fast as the ST but close enough. I combined it with the rest of the logic needed, made an AOI and it works great.

I just wish I could pull the description field from a Logix PLC tag from within PLC logic. That would be the cherry on top - but alas that can't yet be done.

Thanks to all for the assist.

This should run slightly, but perhaps not measurably, faster.

 

[TheWaterboy]

Is the juice here worth the squeeze?
Like you I like to get the code as tight as I can if for no other reason than my own OCD and I think that's true here.
Having said that... now that you pointed it out... Damn it!.

 

[drbitboy]

Lots of juice left for us OCD types

It's still running, generating data, but here is a comparison of four bit-counting algorithms.

 

[drbitboy]

Here are the results for a MicroLogix 1100; I don't know if they will be similar in a Logix/Studio 5000 environment.

​

The timing was used the S:4/S:35 10kHz timer for 1000 iterations of four 32-bit signed integers (MicroLogix Longs). Each of the four Longs were filled with for consecutive bytes of the same value (0x00_00_00_00, 0x01_01_01_01, ..., 0xFF_FF_FF_FF).

The following 1-valued bit counting algorithms were coded and measured:

• CONTRL - no bit counting (control group; measures mean scan time)
• SUBAND - Kernighan's way; SUBtract and AND result to count right-most bit; what @waterboy used; cf. here.
• PARALLEL - fancy parallel counting; cf. here.
• XIC_ - check each bit using /[INDEX[ notation
• LOOKUP - precalculate bits for all possible values (0-255) of a byte; count 8 bits at a time.
  

 

[drbitboy]

I updated the code to unroll the [Kernighan's way] algorithm, which saves about 6% of the overall processing time.

 

[TheWaterboy]

Unroll?

 

[drbitboy]

Unroll?

Yes e.g.

FOR N := 1 TO 3 DO
  Y[I] := N * N;
END_FOR;

is equivalent to this "unrolled" version

N = 0
Y[N] := N * N; N := N + 1;
Y[N] := N * N; N := N + 1;
Y[N] := N * N; N := N + 1;

Optimizing compilers can unroll FOR loops when the number of iterations is known, and even sometimes when the number of iterations is not known. It provides a performance enhancement because the loop index comparison with its implicit GOTO (JMP equivalent) are eliminated.

In our case, the NEQ element 0 was the comparison, so only some JMPs saved, but it does save a few µs per Long.

 

[TheWaterboy]

Ahh, gotcha. I should send you the rest of the code. Your OCD is way stronger than mine.

 

[drbitboy]

...Your OCD is way stronger than mine.

Thanks?