assembly in future C standard HCF Gerry Wheeler

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  • 1. getc/fgets
    Below is a fragment from a program that calculates statistics on x,y data. I want the user to be able to predict one or more predicted values of y from x, given the line of best fit. I have a procedural problem. predict: printf("\npredict y? (y/n): "); if((getc(stdin)=='n')) exit(EXIT_SUCCESS); //if((fgets(response, 1, stdin)=="n")) exit(EXIT_SUCCESS); else { printf("\nenter x: "); scanf("%lf", &xdatum); printf("\ny = %f\n", y_int + (slope * xdatum)); fflush(stdin); goto predict; } It works fine using getc, but when I use fgets execution jumps directly into the else{} block and prompts for x without waiting for user response to the y/n prompt. What am I doing wrong? Richard
  • 2. Justification for "->"?
    A quick search of this group and its FAQ, and elsewhere, have not answered this question to my satisfaction. Apologies if I missed something obvious, either in the literature or my reasoning. Can someone tell me why "->" exists? The compiler knows the difference between a structure and a pointer to a structure, so why can't it just let me write "foo.bar" in both cases and not have to go back and rewrite things when I later decide I want a pointer instead of a value or vice versa? I often change my mind about whether e.g. a function should receive a pointer or the thing itself, and it's mildly inconvenient to have to change all the code that references the members. Is there a historical reason? I read that dmr article on the history of C, and he mentions a time when "foo->bar" would work regardless of the type of "foo", with "bar" just describing an offset and the type of the member value, but this confuses me -- was one not allowed to use the same member name in two different structure types? But even if the original reason was related to this, why was the division kept after the type system got stronger?
  • 3. Unused arguments
    Hi I am considering extending the lcc-win32 compiler to accept int fn(int a, int b,double) { // body of the function } This allows the programmer to specify that the third parameter is not used within the function's body. Does anyone here see a problem with this extension? jacob
  • 4. implement a stack using two queues
    Can any body tell me How to implement a stack using two queues Thax in advance

Re: assembly in future C standard HCF Gerry Wheeler

Postby Walter Banks » Sat, 04 Nov 2006 22:35:39 GMT

As this thread wanders off topic this industry was introduced to a new
mnemonic in Byte article about decoding the undocumented
Motorola 6800 instructions. The HCF (Halt Catch Fire) opcode $DD
or $D9. HFC locked up the processor and cycled the address bus
The author of that article was Gerry Wheeler.

Gerry Wheeler, 54, died October 15, 2006, advanced non-Hodgkins
lymphoma cancer. Gerry made significant contributions to the technology
of the embedded systems world and was a key part of the development
of many household name products.

Programmer, Ham KG4NBB, author, father, husband, active commuity
participant Gerry will be missed by all.

w..


Similar Threads:

1.assembly in future C standard

Peter Nilsson < XXXX@XXXXX.COM > wrote:

(Crossposted to comp.std.c, with followups directed there, hopefully
 appropriately.  The original post discussed the possibility of whether
 __asm or something similar to it would be added to the C standard.)

> Contrary to Richard Heathfield's categorical statement, it is not an
> absolute given that there will never be an asm keyword in C. But it
> is unlikely because it's already clear that the asm keyword in C++ has
> not served to truly standardise the syntax of inline assembly.

One idea that was not mentioned in the original thread (I imagine for
good reason, because it's a half-baked and probably stupid idea that
occurred to me reading your post) would be to allow for some kind of
conditional assembly, just perhaps something like

#pragma assemble
#pragma X86 /* Inner pragma's implementation-defined */
  /* Inline assembly, which the implementation can ignore or not */
#pragma no-assemble
  /* Stock C code for implementations that can't or won't accept the
   * assemble pragma: */
  for( i=1; i < 10; i++ ) {
    foo();
    /* ... */
  }
#pragma end-assemble

The end result would be something like "If the implementation attempts
to inline the assembly code contained within a #pragma assemble
directive, the behavior is implementation-defined.  Otherwise the
assembly code shall be ignored and the C code contained within any
corresponding #pragma no-assemble directive shall be compiled as
though no directives were present."  It would require adding some
duties to the #pragma directive, but it would allow implementors to
take a reasonable shot at using targetted assembly instructions when
appropriate and available, and reverting to ordinary C otherwise.

I'm sure there are reasons why this is stupid and/or impossible, or it
would have been done already :-)

> At the end of the day, the committee could probably spend many man
> weeks deciding issues on an __asm keyword, but for what? Most
> implementations will keep their existing syntax, and most programmers
> who use inline assembly will no doubt continue to prefer the localised
> syntax because it's less cumbersome than any standard syntax.

Indeed, but it's an interesting thought experiment to consider how the
committee *might* add assembly to C if they chose to do so.  (Well,
interesting to me, at least.)

-- 
C. Benson Manica           | I *should* know what I'm talking about - if I
cbmanica(at)gmail.com      | don't, I need to know.  Flames welcome.



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