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Let me tell you a story about a guy named Jed...
A long long time ago (pre-ANSI C), in a galaxy far far away I had worked for a company that had to develop internal "C" coding standards and "Jed" worked on one aspect of the standard while I worked on another. We would hold weekly meetings to reconcile our differences. In attendance, we had other professionals for simple sanity checking and to gain insights from different points of view.
Chris was one of our attendees and was a very experienced software veteran who had plenty of code in various satellite systems orbiting our planet today. By then, Chris was in upper management and graced us with his wisdom when he could.
Well during one of our weekly meetings, "Jed" and I got into a simple disagreement on a Rule about header files. We were at an impasse, so we waited for Chris to arrive and have him make the final decision: about five of us professional engineers were in the room.
When Chris arrived, he heard the arguments, and quickly announced that I was right. (Hence, Jed was wrong).
Well, Jed freaked out and wanted to take the guy outside and teach him a lesson! ... Jed was red-faced, quickly stood up, even took a step towards Chris, and said "Chris, lets just step outside and settle this! I am right and you don't know what you're talking about!" etc etc.
The other attendees and I were duly impressed over Jed's technique of handling technical disagreements. Especially with upper management.
Instead of Jed trying to learn that he *might* be wrong, Jed leaped into the confrontation method of getting his way. Bullies do this because they lack the brain-power to reason through a disagreement. It is a childish trait.
Children are at a huge disadvantage when arguing with "an adult" (or somebody who is much smarter than they are) and they will become very frustrated over their strong desire to assert themselves and their inability to win the mental sparring. They will get physical and/or verbally abusive. Some people out grow this, and some don't.
I think Jed showed his 'abilities' quite well. I find that this is true with so many people on so many subjects. I've seen this behavior many times over. I've seen it here on this forum.
When an "Original Poster", asks a question and people try to answer it (after much refinement of the OP's question) you get these side-bar posts where somebody will start attacking another poster's efforts. And I mean 'attack' and not augment or refine.
I don't have a problem with correcting or clarifying others, or even the occasional sprinkling of sarcasm, but when it is ALWAYS devolves into some vindictive vitriol between a brisling poster and the rest of 'us,' I wonder if it is out of ignorance, malice, or some twisted form of self-entertainment. All three of which are adolescent behaviors. (en.wikipedia.org/.../Adolescence)
Since the regular players here are detail oriented and thus they are savvy enough to know who I'm talking about, I don't think I have to name names.
He is critical enough to figure it out himself, so I would expect that the offender would read this and ask himself if he is demonstrating Ignorance, Malice, Entertainment, or is he being an adult and providing a constructive post before he does so.
And, I hope his "Mea Clupea" (en.wikipedia.org/.../Mea_culpa) will be a silent one, because I'm kind of tired of reading his Hostile Postings (HP).
</rant> --Cpt. Vince Foster 2nd Cannon Place Fort Marcy Park, VA
Jack, Erik,
I don't know how Keil handle bit fields for the C51, but for an ARM it is certainly a bad idea to use them, due to the following reasons:
* Jack must agree with me that bit fields are not really a solid part of the C standard. compilers seem to have artistic freedom when dealing with them which can yield more or less efficient code (packing of structures...). * because all ARM registers are 32 bit, 2 instructions are required to test a bit: a shift to right, then a separate instruction to test the value.
it is much faster to use a 32 bit integer as a container for your bit fields.
I wonder: what is more efficient for a C51? using a bit field or an 8 bit integer?
Tamir,
A bit in C51 is there to specifically use the bit storage area of the CPU. There is a block of 128 bits that are a little like prime real estate. They are particularly useful for boolean operations.
C51 has access to this area with a specific extension.
When considering porting, they are not such a big issue - And I see the usual stubborness being exhibited by a certain poster.
Generally, I would not consider using the bit directly within the code, but would instead use a typedef such as:
#if C51 typedef bit Flag; #else typedef unsigned char Flag; #endif
This is put into a header file with all other port related details.
So whats so difficult about it? Nothing!
Rob, according to whoever hides behind "Jack Sprat", you are wrong, I quote: "Wrapping code in preprocessor directives doesn't make it portable - in fact, it makes it clear that it is non-portable."
evidently you are supposed to make your code portable without using "preprocessor directives"
Erik
Well taken to extremes, that is sheer nonsense; but I do not think (or hope) this is what is being said.
I have plenty of code that runs on different cores where the only difference is a single 'processor/core specific' header file.
At the very least, typedefs that provide specific width variables (e.g., 8, 16, 32) is nothing short of essential.
* Jack must agree with me that bit fields are not really a solid part of the C standard.
If Jack did agree with that, I'd have to disagree with Jack. Until then I'll just disagree with you.
Bit fields are quite a solid part of the C standard. Their only weak aspect lies in many people's idea of what they should be used for. Suffice it to say that, like pretty much all of C's data structures, they're intended for internal data of a C program, but not for its external interfaces.
compilers seem to have artistic freedom when dealing with them which can yield more or less efficient code (packing of structures...).
You have that backwards. Compilers have been granted all that freedom intentionally, to allow them to generate more efficient code. If you find inefficiency, blame it on the platform or the compiler.
If Jack did agree with that, I'd have to disagree with Jack. Until then I'll just disagree with you. verbiage, I think yes, bit fields are described fully in the standard, I guess whoever wrote "not really a solid part" really should have written "this is a section where almost every other word is 'implementation defined'"
The "no easy seamless portability" issues comes to a large extent from the 'implementation defined' sections of the standard. That C would have been miserable to process on some processors had these thing not been 'implementation defined' is another story.
I, for one, "have a lot of fun" processing some data which is a bunch of structures written by a processor where the byte order is "the other way around".
Well, like I just said, writing them to files is exactly what C structs are not for. Don't blame programmer's silly decisions on their tools.
Hans-Bernhard, I did not have control over this, it was so, long before I joined the company. Anyhow, without going into non-disclosure requirements, I think it is the most effective form for transferring this which hold about 75 groups of totally varying information.
Anyhow, if you have a better idea for how to transfer in one transmission about 75 groups of totally varying types of information I would love to hear it since gen 4 of this is about to be defined.
Experienced developers packs/unpacks all data themselves when sending the data on communication links or keeping non-volatile data.
This isn't a limitation of bit fields. But it is always a stupid idea to transmit raw memory structures or to to permanently store raw memory structures.
It doesn't matter if we talk about bit fields or if we talk about unions or even just an array of integers. The data should have a known format. Either pre-defined or containing flags that tells the load code which byte order to expect.
Transmitted or stored data should be described by a 100% complete document and the load/save code should make sure that the document and the reality matches.
By taking care of these issues, I don't have to worry about the next compiler changing the algorithm for packing structures or allocating bit fields from high or low bit. And if I did store the data in an internal flash sector of my ARM, I can modify the code a bit and instead write the same data to a SD memory and move that SD memory to a PC and correctly read the data. Or I can add XMODEM and transmit the saved data to a different unit using whatever processor and it will be able to process the XMODEM data and use the same code to restore the original information.
Experienced developers packs/unpacks all data themselves when sending the data on communication links or keeping non-volatile data. easy when you control both ends, I do not. This isn't a limitation of bit fields. But it is always a stupid idea to transmit raw memory structures or to to permanently store raw memory structures. please define 'raw' ? Transmitted or stored data should be described by a 100% complete document it is, of course, how else could i use it?
erik