 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Microcontroller and PC projects : Reset/empty string ARRAY$ ?
Page 1 of 2   |
|||||
| Author | Message | ||||
electricat Senior Member  Joined: 30/11/2020 Location: LithuaniaPosts: 240 |
So, I created var inside SUB LOCAL dirct$(255) length 16 Time to time I need clear/reset/empty values in array. I could do it cycling --> dirct$(n) = "" But it looks to me, it might be some simple/faster way?? I wanted to use ERASE and re-declare, but this seems ERASE will not to work inside SUB Any advice please... |
||||
| twofingers Guru  Joined: 02/06/2014 Location: GermanyPosts: 1456 |
I would also like a solution for that. Redim a string array with erase works with Erase/Dim within subs.* Regards Michael * See FM02000! Edited 2025-03-11 04:40 by twofingers causality ≠ correlation ≠ coincidence |
||||
| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9800 |
Sub test Const slen=16 Local dirct$(255) length slen dirct$(255)="1234567890abcdef" dirct$(0)="ABCDEFGHIJKLMNOP" Print dirct$(0),dirct$(255) Local integer a%=Peek(varaddr dirct$()) Memory set byte a%,0,(Bound(dirct$(),1)+1)*(slen+1) Print dirct$(0),dirct$(255) End Sub |
||||
javavi Guru Joined: 01/10/2023 Location: UkrainePosts: 401 |
@matherp Is there a clever way to reserve a byte array in the RAM variable area (not in the heap) and have byte-by-byte access to it using the PEEK POKE commands? Let's say two arrays of 200-500 bytes each. Edited 2025-03-11 05:12 by javavi |
||||
| electricat Senior Member Joined: 30/11/2020 Location: LithuaniaPosts: 240 |
@Peter, For me looks like memset(myArray, 0, sizeof(myArray)) but in MMBasic  ? Recently I was interested in varaddr etc. manipulations but I failed to find in documentation more detailed info how vars are stored. Played a bit peeking poking memory, and found it interesting  Thank you boys. Will play. Edited 2025-03-11 05:11 by electricat |
||||
| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9800 |
No: it's a hash table Edited 2025-03-11 05:17 by matherp |
||||
| twofingers Guru Joined: 02/06/2014 Location: GermanyPosts: 1456 |
Thanks Peter! I will play with it! Regards Michael causality ≠ correlation ≠ coincidence |
||||
CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2121 |
MicroMite: Unless this is peculiar to SUB, this must be a change (possibly to do with hashed variables). My code for SPLIT() routine ERASEs and DIMs an array in a FUNCTION() h |
||||
| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2121 |
My work was aimed at MicroMites and so I don't think it will be useful to you. I did a lot of work on this to come up with my UBOUND() function for interest's sake...  and some code that helped option base 0 dim a$(9) dim integer fred const bim=99 fred=1 ? for n=0 to 511 step 16 b$="" ? Hex$(n,4);" "; for m=0 to 15 q=PEEK(VARTBL, n+m) ? hex$(q,2);" "; if q<32 or q>126 then q=46 b$=b$+chr$(q) next ?" ";b$ fred=fred+1:If fred>4 then fred=1:print next erase a$ fred=1 ? for n=0 to 511 step 16 b$="" ? Hex$(n,4);" "; for m=0 to 15 q=PEEK(VARTBL, n+m) ? hex$(q,2);" "; if q<32 or q>126 then q=46 b$=b$+chr$(q) next ?" ";b$ fred=fred+1:If fred>4 then fred=1:print next dim bb$(5), a$(2) fred=1 ? for n=0 to 511 step 16 b$="" ? Hex$(n,4);" "; for m=0 to 15 q=PEEK(VARTBL, n+m) ? hex$(q,2);" "; if q<32 or q>126 then q=46 b$=b$+chr$(q) next ?" ";b$ fred=fred+1:If fred>4 then fred=1:print next I have discussed this on and off here - just do a search for UBOUND h Edited 2025-03-11 05:42 by CaptainBoing |
||||
| electricat Senior Member Joined: 30/11/2020 Location: LithuaniaPosts: 240 |
@CaptainBoing I highly like this  Brings back memories of zx spectrum. Games hacking and such.Devs` have no time to describe things like this. But I can understand |
||||
| javavi Guru Joined: 01/10/2023 Location: UkrainePosts: 401 |
@CaptainBoing @matherp How wasteful is the memory usage in this hash table for a microcontroller with limited memory resources? |
||||
| electricat Senior Member Joined: 30/11/2020 Location: LithuaniaPosts: 240 |
Might be doubtfull idea, but SPRITE READ, BLIT READ creates kind of 'protected memory' You only need to find address where it is stored (search pattern) and use it in a way you want But I do not know sprites or blit memory management works. Peter knows As I said - doubtfull idea. But we used to do all kind of nonsenses with ZX spectrum :D |
||||
| electricat Senior Member Joined: 30/11/2020 Location: LithuaniaPosts: 240 |
wwwohaaa Memory set byte a%,0,(Bound(dirct$(),1)+1)*17 timer diff ->> 0.072for a=0 to 255 timer diff ->> 3.86 !!dirct$(a)="" next a means 53x faster  Edited 2025-03-11 06:35 by electricat |
||||
| Bleep Guru Joined: 09/01/2022 Location: United KingdomPosts: 548 |
I believe it'll be 17 times that for your For Next loop, currently you are only clearing 256 bytes, Peters is clearing 256*17 bytes? Presumably the string may be gone, but the data may still be there in the unclear memory. Regards Kevin Edited 2025-03-11 07:11 by Bleep |
||||
| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2121 |
To be clear about this - my point of reference for all this is Micromite Mk2 (PIC32MX170-based). The graphic above shows the VARTBL memory layout for that 'mite, which does not use hashed variables and is unlikely ever to do so - being considered "finished" and updates to the firmware are for serious bugs only. Each variable there takes 64 bytes in the table - I can account for around 50 of them so not that bad at all and a small price to pay to keep things a nice "CPU-sized" number. The "worst waste" is using undimensioned strings - they are all 255 bytes long - even A$="Hello World!" and the syntactically accepted LENGTH is ignored for single variables. I think this extends to all 'mite flavours - anyone? You can make things a bit better if you are REALLY low on RAM by making sure all your string variables are part of an array and then using LENGTH, but it doesn't make for easy reading and there is a tiny speed penalty. Using a CONST to identify specific members of the array can help, but it's an awful faf and arguably just moving the problem to flash storage from RAM (but this does save 500 bytes): 'very convuluted but you get the idea Const Greeting=1 Const Goodbye=2 Option Base 1 Dim m$(2) =("wotcha","tata") Length 10 Print m$(Greeting) Print m$(Goodbye) In all honesty, I have yet to be seriously hampered by this and it really doesn't stop me sleeping. Birds. Birds stop me sleeping. h Edited 2025-03-11 21:26 by CaptainBoing |
||||
| twofingers Guru Joined: 02/06/2014 Location: GermanyPosts: 1456 |
I think this is only correct for PicoMites for lengths of 8 characters or more. https://www.thebackshed.com/forum/ViewTopic.php?FID=16&TID=17750 Regards Michael causality ≠ correlation ≠ coincidence |
||||
| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4721 |
Integers and floats are 64 bits (8 bytes). For integers and floats a reserved memory block is used (28kbyte) that is not part of the dynamic heap. A string up to 8 characters fits inside 64bits, and could become part of this reserved memory block (so it is not part of the dynamic heap). That is pefectly in line with Captains vatrtable analysis above (March 10 post). Volhout Edited 2025-03-11 22:08 by Volhout PicomiteVGA PETSCII ROBOTS |
||||
thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4200 |
- Each MMBasic variable takes ~64 bytes in the variable table. - Most of this is used by the name, type, dimensions, etc. - 8 of these bytes are used for storage, enough for a 64-bit FLOAT, INTEGER, a very short string (7/8 chars? - but not on Micromites or currently MMB4L) or a pointer into the heap for a larger string or array. - Space on the heap is always allocated in 256 byte pages ... hence a larger string always taking 256 bytes and the minimum allocation for an array being 256 bytes. Best wishes, Tom MMBasic for Linux, Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
||||
| thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4200 |
On reflection I suspect it is one byte containing the current length and *7* characters. Tom MMBasic for Linux, Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
||||
| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9800 |
Doesn't work like that. The vartbl entry still contains a pointer so nothing else needs changing. For short strings it points to the second element of the dimension array which is repurposed to contain the string |
||||
| Page 1 of 2 |
|||||
 Print this page |
