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In a recent posting elrond@titan.tsd.arlut.utexas.edu (Brad Hlista) writes:
| I am having a problem of getting an allocated block of far memory
| to return float values.  Here is how variables are declared and dereferenced:

| far *ptr;

I think this is the big part.  An int pointer is not the same as a float
pointer.  The following program works for me (MSC).

#include <stdio.h>
#include <malloc.h>
int main(void);

int main()
{
    int i;
    float far *start;
    float far *p;

    start = (float far *) _fmalloc(1000*sizeof(float));

    if (start != NULL) {
        printf("Good.\n");
        for (p=start,i=0 ; i<1000 ; i++)
            *(p++) = 3.1415927;
        for (p=start,i=0 ; i<10 ; i++)
            printf("%f\n", *(p++));
    }
    else
        printf("Oh shit.\n");
    return(0);
}

-- 
Jim Wright
jwright@atanasoff.cs.iastate.edu

In article <565@titan.tsd.arlut.utexas.edu> elrond@titan.tsd.arlut.utexas.edu (Brad Hlista) writes:
|I am having a problem of getting an allocated block of far memory
|to return float values.  Here is how variables are declared and dereferenced:
|
|far *ptr;
|
|main()
|{
|int i;
|
|	ptr=(float *) farmalloc(100000);
|
|	f(i=0;i<1000;i++)
|		*(ptr+i)=3.1415927;

Should be:	*((float *)(ptr+i)) = 3.1415927;

	Otherwise the "far" declaration of "ptr"
	will force a type conversion to the default
	of type "int". The way you have it the
	contents of of *(ptr+i)" contains an int
	value which is coerced back to float
	in the printf statement.

|	for(i=0;i<10;i++)
|		printf(" %f", (float) *(ptr+i) ) ;  /* is yielding 3.00000 */

Should be	printf(" %f", *((float *)(ptr+i)) ) ;  /* is yielding 3.1415927 */

|}
|
|Can someone please help me understand what is going on?
|Thanks.

	You need to ensure that either by default
	or by explicit declaration that
	sizeof(far) == sizeof(float); is there a
	"far long" type? Better yet, a "far float"?

	I didn't actually try this so if your compiler
	barfs on "*((float *)ptr)" where "ptr" is a
	"far *" declaration, well... you could try
	"far float * ptr;", etc...

Cheers,
-- 
  .::.	 Bruce Becker	Toronto, Ont.
w \@@/	 Internet: bdb@becker.UUCP, bruce@gpu.utcs.toronto.edu
 `/c/-e	 BitNet:   BECKER@HUMBER.BITNET
_/  \_	 In the future the term "wife" will have no gender significance

Two suggestions:

  1)  Your main problem is that you need to use the declaration:

      far float *ptr;

      I won't even try to explain what happens otherwise.

  2)  You really should use "ptr[i]" rather than "*(ptr+i)".  It effectively
      does the same thing, but it makes for much cleaner and much more
      readable code.

In article <990@becker.UUCP> bdb@becker.UUCP (Bruce Becker) writes:
Bruce> Xref: sics.se alt.msdos.programmer:153 comp.sys.ibm.pc:29919

Bruce> In article <565@titan.tsd.arlut.utexas.edu> elrond@titan.tsd.arlut.utexas.edu (Brad Hlista) writes:

Bruce> |far *ptr;

Bruce> |main()

[... unimportant things deleted ...]

Bruce> |	f(i=0;i<1000;i++)
Bruce> |		*(ptr+i)=3.1415927;

Bruce> Should be:	*((float *)(ptr+i)) = 3.1415927;

(* GAACK *) This means you should use the i'th INTEGER location, not float!
Wow. The effect when printing out would be quite a sight...

No, the correct syntax would be : *((float *)ptr + i)

This way, you tell the compiler that ptr really is a float pointer, then
offset the whole thing with i.

In your solution, the offset would be 2*i bytes (2 = sizeof(int)). In mine,
the offset would be 4*i bytes (4=sizeof(float)) !!!!

Bruce> |	for(i=0;i<10;i++)
Bruce> |		printf(" %f", (float) *(ptr+i) ) ;  /* is yielding 3.00000 */

Bruce> Should be	printf(" %f", *((float *)(ptr+i)) ) ;  /* is yielding 3.1415927 */

Likewise here. Use *((float)ptr + i) instead !

Bruce> 	sizeof(far) == sizeof(float); is there a
Bruce> 	"far long" type? Better yet, a "far float"?

Wow. sizeof(far) ! Never seen that before. This would mean 'far int', which is
not (as far as I know) permitted in TC.
far is only applied on pointer and functions, to tell the compiler you need a
4-byte adress to get those objects. Thus, far is a modifier, not a type.
Now, about int. int is the same as short in TC, a 2-byte integer. float is a
4-byte float.

One IMPORTANT rule when you program in C: NEVER assume anything about the size
of differnet types. NEVER !!!!!

Bruce> 	I didn't actually try this so if your compiler
Bruce> 	barfs on "*((float *)ptr)" where "ptr" is a
Bruce> 	"far *" declaration, well... you could try
Bruce> 	"far float * ptr;", etc...

Quite surprising. I just tried it with Turbo C v 2.0, writing 
*((float *)ptr+i), and it worked just nice. writing *((float *)(ptr+i)) gave
me 0.000000 when I tried it...


--
Tommy Levitte 
	gizmo@nada.kth.se
	gizmo@kicki.stacken.kth.se
	gizmo@ttt.kth.se