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Hi all Below is the result of some debugging. I have isolated some code from a bigger project and have put it into a stand-alone project.
I basically don't understand why I can do right bit-shifting and AND'ing on single line, when I can't do left bit-shifting and AND'ing on single line.
If it isn't a bug, then what have I missed?
I have included many comments to describe my problem
#include <ADUC832.H> #include <string.h> void main(void) { char ascii[] = "MC"; unsigned char pdu[3]; int w=0, r=0, len; char ch1, ch2, rr, rl; /* This is what I want to do: while-loop run 1: 1: Assign to var 'ch1': ch1 = 'M' (= 0x4D = 0100 1101) 2: Assign to var 'ch2': ch2 = 'C' (= 0x43 = 0100 0011) 3: Assign to var 'w' : w = 0 4: OR together the following: ((ch1 >>(w%7))&0x7F) | ((ch2 <<(7-(w%7)))&0xFF); <=> 0100 1101 | 1000 0000 <=> 1100 1101 <=> 0xCD while-loop run 2: 1: Assign to var 'ch1': ch1 = 'C' (= 0x43 = 0100 0011) 2: Assign to var 'ch2': ch2 = 0x00 3: Assign to var 'w' : w = 1 4: OR together the following: ((ch1 >>(w%7))&0x7F) | ((ch2 <<(7-(w%7)))&0xFF); <=> 0010 0001 | 0000 0000 <=> 0010 0001 <=> 0x21 */ len=strlen(ascii); while (r<len) { // ------ First OR-part ----------------------- // -------Both versions below are OK ---------- // -- VER 1: OK // ch1 = ascii[r]; // rr = (w%7); // ch1 = (ch1 >> rr) & 0x7F; // -- VER 2: OK ch1 = (ascii[r] >> (w%7)) & 0x7F; // Bit-shifting and AND'ing // may be done in one line // ------ Second OR-part ----------------------------- //------- Both versions below are NOT OK ?? ---------- // -- VER 1: OK ch2 = ascii[r+1]; rl = (7-(w%7)); ch2 = (ch2 << rl) & ((char)0xFF); // Bit shift and AND'ing can be // done in one line, IF type cast // is used - why? // ch2 = ch2 & 0xFF; // If splitting into new line // type cast is not required? // -- VER 2: NOT OK // ch2 = (ascii[r+1] << (7-(w%7))) & 0xFF; // type cast doesn't help // ch2 = ch2 & 0xFF; // AND'ing must be on seperate line ? //---------------------------------------------------------------- // IS THIS A BUG ?? //---------------------------------------------------------------- // Why can we bit-shift and do the AND'ing in a single line // for the first OR-part above, but cannot do it for the second // OR-part where bit-shifting and AND'ing must be on two seperate // lines ??? //---------------------------------------------------------------- // ------ Do the actual OR'ing ------- pdu[w]= (ch1 | ch2) ; if ((w%7)==6) r++; r++; w++; } pdu[w]=0; // terminator //---------------------------------------------------------------- // Run to here in debugger and look at content of // local variable 'pdu'. // When using 'NOT OK' versions from above // pdu will contain {0x4D, 0x21, 0x00} // and not {0xCD, 0x21, 0x00} as the 'OK' versions // produce. //---------------------------------------------------------------- while(1); }
I did not go for an extended study of the C standard to see what was right and what was wrong
Still refusing to read the manual, then?
but I do believe that whether the typecast is required or not should be the same in both cases
Facts, man, facts. This is engineering, not religion.
I sent an 'inconsistency report' to support
Oh dear.
Why would I, as you see I solved the problem.
I have succesfully coded C for more than 15 years and really do not have any interest, whatsoever, in why things are as they are. That I know enough to program in C and figure out what is wrong when it does not work is more than enough for me.
Of course - and fortunately, I do not have the ability to code C in such a way that no one can figure out what it is doing. That part I leave to those that "study every detail of the manual".
I have had Kochans book since day one and that is my manual. Yes, you probably need a severe study of e.g. K&R to find out if a union will have an odd or even length when it is a long and 5 chars, but I REALLY do not care about such.
Erik
Is that so terrible, I did not send a 'bug report', I did not request a fix, I stated "no reply required". I just pointed out the (if you insist - percieved) inconsistency. If the Keil people study decide there is no inconsistency, I am sure they have a trashcan.
No. You changed the code around until it gave the result you expected. There was no problem to solve other than your false expectations.
I have succesfully coded C for more than 15 years and really do not have any interest, whatsoever, in why things are as they are.
This is exactly the reason there is so much sloppy, buggy code out there. When using a language like 'C' you need to have a good understanding of what is going on behind the scenes. I'm afraid that the best way of doing that is... reading the manual.
That I know enough to program in C and figure out what is wrong when it does not work is more than enough for me.
Thing is, in the example you gave you didn't figure out what was wrong. You did not understand why the code behaved the way it did.
You seem to have a very negative attitude to those who read the manual. This is strange considering the frequency with which you encourage others to do so.
I have had Kochans book since day one and that is my manual.
Well, either the book is inadequate or you haven't read it. Let's see: I wonder if I can guess which one is the case?
I just pointed out the (if you insist - percieved) inconsistency.
There is no inconsistency. If you had understood the code you had written you would not have been surprised by the result.
I did not send a 'bug report'
Let's think about this: You had two pieces of code that you thought should give the same result. That means that either you were wrong or the compiler was wrong. I don't imagine you emailed Keil to tell them you were wrong, did you?
Is that so terrible
Yes. Read the manual instead of wasting peoples time.
You seem to have a very negative attitude to those who read the manual. This is strange considering the frequency with which you encourage others to do so. absolutely NOT! I just have " very negative attitude" about your hammering that "your" manual is mandatory. My 'manual' has sufficed me for 15 years. You may, very well know more about the intricacies of special cases in C, I have no probloem with that, I do not need them.
I have had Kochans book since day one and that is my manual. Well, either the book is inadequate or you haven't read it. Let's see: I wonder if I can guess which one is the case? The book in not "inadequate", and I have read it (and still refer to it on occasion); that it might not cover every nook and cranny of the finer, more obscure, details of the language (which, if you use them, will result in code that only the few chosen can understand) is not a problem for me.
I am more interested in studying the finer details of what to code than the finer details of how to code. I have seen lots of s**t from 'professional fully implemeted understanding of C' and none from 'professional fully implemeted understanding of the processor'
Read the manual instead of wasting peoples time.
1) did I ask YOU to waste time posting here.
2) if you took the time to read the thread (instead of wasting it as you state you do by responding here) you would see that I did not start this thread, just posted that what I had seen might be an answer to the OPs problem.
3) you are welcome to 'hate' me, my skin is thick.
Ps could your attitude against me be that you are offended that I often post "this is not a processor to just willy nilly code C for. You actually need to know the hardware and THINK, not just code 'good C'". I know you will not agree but '51 C is not "just C"
absolutely NOT! I just have " very negative attitude" about your hammering that "your" manual is mandatory.
The 'C' standard defines the language and is therefore the best reference. I would suggest that if you dispute this you are plain wrong.
that it might not cover every nook and cranny of the finer, more obscure, details of the language (which, if you use them, will result in code that only the few chosen can understand) is not a problem for me.
The problem you encountered was with arithmetic using simple integer data types. If your book doesn't cover that it is seriously flawed. I suspect it probably does and the real problem is that you haven't read the appropriate section.
I am more interested in studying the finer details of what to code than the finer details of how to code.
A programming language is a tool. If you aren't prepared to learn how the tool works you won't be able to use it properly. In the context of a programming language this will result in buggy, inefficient code.
did I ask YOU to waste time posting here.
No. I was thinking of the support people who have to read the same old questions over and over again from those who haven't read the manual.
if you took the time to read the thread (instead of wasting it as you state you do by responding here) you would see that I did not start this thread, just posted that what I had seen might be an answer to the OPs problem
I did read the thread and I did notice that you didn't start it. I also noticed that you had again posted code showing a fundamental lack of understanding of the 'C' language and thought that I'd take the opportunity to offer you more encouragement to read the manual and improve your programming skills.
you are welcome to 'hate' me, my skin is thick
Please don't confuse a little constructive criticism with hatred. This is a professional forum not a playground.
You actually need to know the hardware and THINK, not just code 'good C'".
Of course. But you do need to be able to code good 'C'.
I know you will not agree but '51 C is not "just C"
'C' is 'C'. Just because you are using it on an 8051 is no excuse to write poor 'C'.
Read the manual!
I have seem that from ever so many that are totally fluent in C never from someone that is "fluent in the '51".
just an example A Cidiot will have switches all over the place when an if, else if construct is much more efficient in Keil C. yes, I have studied the tool.
Of course. But you do need to be able to code good 'C'. please define "good C", my definition is "bug free" and efficient, not "elegant".
'C' is 'C'. Just because you are using it on an 8051 is no excuse to write poor 'C'. see above.
Please don't confuse a little constructive criticism with hatred. This is a professional forum not a playground. First please note the quotes, I used a word that did not fit exactly. Constructive criticism my a.., I posted a question, what about just answerinmg it straight.
Again, I succesfully code functional time efficient bug free systems, what is the problem?. That I do not 'like' 'char' is that a problem?.That I wonder why a typecast that I did insert is only needed in one case, is that a problem?. That I have found that some 'elegant' C constructs are inefficient when running on '51 hardware and thus advise against them is that a problem?. Should I preact the gospel of "real C" and ignore the platform I work on?. I once laid off a person who reacted to "change that, it takes too long to process" with "then it will not be rea;l C". My 'gospel' is fast code, since my area requires that.
please define "good C", my definition is "bug free" and efficient, not "elegant".
You can't write bug free or efficient code if you don't understand the rules of the programming language you're using.
Returning to the example you posted:
You had a simple piece of code that didn't give the results you expected. So, rather than find out why it behaved as it did you modified it until it did give the result you expected. By the end of this process you had no idea *why* one piece of code appeared to work and the other didn't.
The problem with this 'hack it and see' approach is that you cannot be sure that the code that does appear to give the correct result is actually correct, as you continue to believe the code that gives the wrong result should also be correct. Finally your misplaced self confidence leads you to assume that you've encountered an 'inconsistency' in the way the compiler generates code and that you have stumbled on a workaround.
This might be an acceptable approach for a hobbyist but it certainly isn't for a professional.
Again, I succesfully code functional time efficient bug free systems, what is the problem?
The problem is that they most probably aren't bug free.
That I wonder why a typecast that I did insert is only needed in one case, is that a problem?
Yes, it is. If you don't understand why you needed to use the cast then you are quite possibly just masking a problem. There are very few situations in 'C' where it is necessary to use a cast.
Should I preact the gospel of "real C" and ignore the platform I work on?
Why do you think that writing correct 'C' code somehow precludes understanding the target platform? You seem to think that if you learn how to write correct 'C' then somehow you won't be able to target the 8051? Or am I missing the point?
My 'gospel' is fast code, since my area requires that.
Maybe, but all areas require correct code.
you sure are. The Cidiots preach using malloc, function pointers, switch etc regardless of the platform and compiler
My 'gospel' is fast code, since my area requires that. Maybe, but all areas require correct code. Agreed, but what makes you think my bug free code is not correct? is that because use C instead of preaching it? or is that because I will use many lines for clarity rather than to cram as much as possible into one line to achieve the same in an incomprehensible way? or is that because I think execution time instead of elegance? or is that beacuse I actually occasionally check the assembler output to see if the compiler is time efficient in compiling a given construct however 'right' it may be to a Cidiot? or is it because I do not suppress warnings, but fix them? My original post in this thread was triggered by a warning that DID show the line with the problem, which I then fixed.
I am rally amazed that you can think that the more than a million units running with my code in them without complaints are an indication that they most probably aren't bug free