Troubling Alignment (I think) issue.

[Kevin]

Hey, I was hoping someone out here might be able to clue me in on some
alignment issues I'm having. Hopefully I can explain this best
through code below. ACSign and MyACSign functions below get compiled
(gcc) into one library, where as the code that executes these
functions gets compiled into a seperate library. Calls to MyACSign
work fine, calls to the straight ACSign do not and I believe it is due
to alignment issues, but I can't pinpoint how. This <i>should</ihave
been very elementary. Any help is of course greatly appreciated,

- Kevin
Function Code:
************************************************** ******************
double ACSign ( double a) {
if (a 0.0)
return(1.0);
else if (a < 0.0)
return(-1.0);
}

double * MyACSign (double * a) {
if (*a 0.0)
*a = 1.0;
else if (*a < 0.0)
*a = -1.0;
return a;
}

Execution Code:
************************************************** ******************
double test = 0 ;
double test1 = 0;
test = 0.707107;
test1 = test * -1;

printf("Locations: %u, %u\r\n", &test, &test1);

printf("0Double: %f, %f", test, test1);
printf("1Double: %f, %f", ACSign(test), ACSign(test1));
printf("2Double: %i, %i", (char)ACSign(test), (char)ACSign(test1));

printf("3Double: %f, %f", 0.707107, -0.707107);
printf("4Double: %f, %f", ACSign(0.707107), ACSign(-0.707107));
printf("5Double: %i, %i", (char)ACSign(0.707107),
(char)ACSign(-0.707107));

printf("6Double: %f, %f", test, test1);
printf("7Double: %f, %f", *(double*)MyACSign(&test),
*(double*)MyACSign(&test1));
printf("8Double: %i, %i", (char)*(double*)MyACSign(&test),
(char)*(double*)MyACSign(&test1));
************************************************** ******************
The output I get is:
Locations: 4263558272, 4263558264
0Double: 0.707107, -0.707107
1Double: 0.707107, -0.707107
2Double: -98, -98
3Double: 0.707107, -0.707107
4Double: 0.707107, 0.000000
5Double: -98, -98
6Double: 0.707107, -0.707107
7Double: 1.000000, -1.000000
8Double: 1, -1

[Ben Pfaff]

Kevin <ke********@gmail.comwrites:

Hey, I was hoping someone out here might be able to clue me in on some
alignment issues I'm having.

I doubt your problems have anything to do with alignment.
Rather, I suspect that you are not properly declaring the
functions in a header file, e.g.
double ACSign(double);
double *MyACSign(double *);
The prototypes (the bits in parentheses) are optional but they
help the compiler to check the calls.
--
char a[]="\n .CJacehknorstu";int putchar(int);int main(void){unsigned long b[]
={0x67dffdff,0x9aa9aa6a,0xa77ffda9,0x7da6aa6a,0xa6 7f6aaa,0xaa9aa9f6,0x11f6},*p
=b,i=24;for(;p+=!*p;*p/=4)switch(0[p]&3)case 0:{return 0;for(p--;i--;i--)case+
2:{i++;if(i)break;else default:continue;if(0)case 1:putchar(a[i&15]);break;}}}

[santosh]

On Wednesday 07 Nov 2007 1:57 am Kevin <ke********@gmail.comwrote in
article <11**********************@i38g2000prf.googlegroups .com>:

Hey, I was hoping someone out here might be able to clue me in on some
alignment issues I'm having. Hopefully I can explain this best
through code below. ACSign and MyACSign functions below get compiled
(gcc) into one library, where as the code that executes these
functions gets compiled into a seperate library. Calls to MyACSign
work fine, calls to the straight ACSign do not and I believe it is due
to alignment issues, but I can't pinpoint how. This <i>should</ihave
been very elementary. Any help is of course greatly appreciated,

- Kevin
Function Code:
************************************************** ******************
double ACSign ( double a) {
if (a 0.0)
return(1.0);

Both the parenthesis and the decimal point are unnecessary.

else if (a < 0.0)
return(-1.0);

Similarly here.

}

double * MyACSign (double * a) {
if (*a 0.0)
*a = 1.0;
else if (*a < 0.0)
*a = -1.0;
return a;
}

Execution Code:
************************************************** ******************
double test = 0 ;
double test1 = 0;
test = 0.707107;
test1 = test * -1;

printf("Locations: %u, %u\r\n", &test, &test1);

No. To print pointers use the '%p' specifier and cast the corresponding
argument to void *. Also the '\r' is not only not necessary but may
cause problems. The C Standard library translates a '\n' to whatever
the system uses as end-of-line.

printf("0Double: %f, %f", test, test1);
printf("1Double: %f, %f", ACSign(test), ACSign(test1));
printf("2Double: %i, %i", (char)ACSign(test), (char)ACSign(test1));

What's the point in casting a double value to a char and then passing
them inccorrectly to printf after telling it to look for an int? Use
the '%c' format to print a char.

printf("3Double: %f, %f", 0.707107, -0.707107);
printf("4Double: %f, %f", ACSign(0.707107), ACSign(-0.707107));
printf("5Double: %i, %i", (char)ACSign(0.707107),

Same problems again. Besides what are you expecting to see after a lossy
cast?

(char)ACSign(-0.707107));

printf("6Double: %f, %f", test, test1);
printf("7Double: %f, %f", *(double*)MyACSign(&test),

No. Use *(MyACSign(&test)).

*(double*)MyACSign(&test1));

Similarly.

printf("8Double: %i, %i", (char)*(double*)MyACSign(&test),
(char)*(double*)MyACSign(&test1));

Again this mysterious cast to a char value.

************************************************** ******************
The output I get is:
Locations: 4263558272, 4263558264
0Double: 0.707107, -0.707107
1Double: 0.707107, -0.707107
2Double: -98, -98
3Double: 0.707107, -0.707107
4Double: 0.707107, 0.000000
5Double: -98, -98
6Double: 0.707107, -0.707107
7Double: 1.000000, -1.000000
8Double: 1, -1

As you have invoked undefined behaviour in several places you could get
any kind of output. I suggest you fix the obvious errors and recompile
and rerun.

[Kevin]

Bingo, I stumbled upon the same answer at the same time - thanks!. I
missed the implied declaration warning in the compiling code and my
partners missed this one function in the header.

Thanks again!

- Kevin
On Nov 6, 3:37 pm, Ben Pfaff <[e-mail]:

Kevin <[e-mail]:

Hey, I was hoping someone out here might be able to clue me in on some
alignment issues I'm having.

I doubt your problems have anything to do with alignment.
Rather, I suspect that you are not properly declaring the
functions in a header file, e.g.
double ACSign(double);
double *MyACSign(double *);
The prototypes (the bits in parentheses) are optional but they
help the compiler to check the calls.
--
char a[]="\n .CJacehknorstu";int putchar(int);int main(void){unsigned long b[]
={0x67dffdff,0x9aa9aa6a,0xa77ffda9,0x7da6aa6a,0xa6 7f6aaa,0xaa9aa9f6,0x11f6}*,*p
=b,i=24;for(;p+=!*p;*p/=4)switch(0[p]&3)case 0:{return 0;for(p--;i--;i--)case+
2:{i++;if(i)break;else default:continue;if(0)case 1:putchar(a[i&15]);break;}}}

[John Gordon]

In <11**********************@i38g2000prf.googlegroups .comKevin <ke********@gmail.comwrites:

Calls to MyACSign work fine, calls to the straight ACSign do not

You're more likely to get useful responses if you describe *exactly* what
is wrong, rather than just saying "it doesn't work".

The output I get is:
Locations: 4263558272, 4263558264
0Double: 0.707107, -0.707107
1Double: 0.707107, -0.707107
2Double: -98, -98
3Double: 0.707107, -0.707107
4Double: 0.707107, 0.000000
5Double: -98, -98
6Double: 0.707107, -0.707107
7Double: 1.000000, -1.000000
8Double: 1, -1

Which of these do you think are wrong, and what were you expecting instead?

--
John Gordon A is for Amy, who fell down the stairs
go****@panix.com B is for Basil, assaulted by bears
-- Edward Gorey, "The Gashlycrumb Tinies"

[Eric Sosman]

Kevin wrote On 11/06/07 15:27,:

Hey, I was hoping someone out here might be able to clue me in on some
alignment issues I'm having. Hopefully I can explain this best
through code below. ACSign and MyACSign functions below get compiled
(gcc) into one library, where as the code that executes these
functions gets compiled into a seperate library. Calls to MyACSign
work fine, calls to the straight ACSign do not and I believe it is due
to alignment issues, but I can't pinpoint how. This <i>should</ihave
been very elementary. Any help is of course greatly appreciated,

My bet is that the calling code has no declarations
for the called functions. This will cause a C99 compiler
to emit a diagnostic, but causes older compilers to assume
that the undeclared function returns an `int' value. Since
the two functions actually return `double' and `double*',
the behavior is undefined. In one case you get garbage:
the returned `double' is getting treated as an `int', or
the function's value is getting plucked from an integer
register instead of from the floating-point register where
the function put it, or something of that sort. In the
other case, it looks like you're lucking out: the `double*'
value seems to be returned in the same way an `int' would
have been, and the conversion from `int' to `double*' is
apparently not damaging it -- but that's not something you
can count on.

double ACSign ( double a) {
if (a 0.0)
return(1.0);
else if (a < 0.0)
return(-1.0);

... and if a == 0.0 exactly ...?

}

--
Er*********@sun.com

[Keith Thompson]

santosh <sa*********@gmail.comwrites:

On Wednesday 07 Nov 2007 1:57 am Kevin <ke********@gmail.comwrote in
article <11**********************@i38g2000prf.googlegroups .com>:

[...]

>double ACSign ( double a) {
if (a 0.0)
return(1.0);

Both the parenthesis and the decimal point are unnecessary.

> else if (a < 0.0)
return(-1.0);

Similarly here.

>}

[...]

Yes, the parentheses are unnecessary, and as a matter of style
I strongly prefer *not* to use extra parentheses. So:
return 1.0;
rather than
return(1.0);
The latter looks too much like a function call, and it isn't one.
(But it's perfectly legal, and K&R1 used that style.)

As for the decimal point, presumably you aren't suggesting
return 10;
rather than
return 1.0;
8-)}

I prefer to use floating-point literals for floating-point numbers.
Yes, you can use
return 1;
but ``1'' is of type int, and is implicitly converted to double. The
compiler will almost certainly generate exactly the same code as for
return 1.0;
but I find the more explicit form clearer.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
Looking for software development work in the San Diego area.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Richard Heathfield]

Keith Thompson said:

Keith Thompson (The_Other_Keith) [...]
<http://www.ghoti.net/~kst>

On that page, you write:

"Versions of this page are available at
<http://www.users.cts.com/king/k/kst/and..."

but the cts link is dead.

No skin, etc, but I thought you might like to know! :-)

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Keith Thompson]

Richard Heathfield <rj*@see.sig.invalidwrites:

Keith Thompson said:

>Keith Thompson (The_Other_Keith) [...]
<http://www.ghoti.net/~kst>

On that page, you write:

"Versions of this page are available at
<http://www.users.cts.com/king/k/kst/and..."

but the cts link is dead.

No skin, etc, but I thought you might like to know! :-)

Yeah, my cts.com account died years ago, and I haven't updated my
ghoti.net home page in even longer. I suppose I should either update
it or drop it from my sig.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
Looking for software development work in the San Diego area.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Richard Heathfield]

Keith Thompson said:

<snip>

Yeah, my cts.com account died years ago, and I haven't updated my
ghoti.net home page in even longer. I suppose I should either update
it or drop it from my sig.

I'd leave it until tomorrow if I were you.

Oh, you did. :-)

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Nick Keighley]

On 6 Nov, 20:46, santosh <[e-mail]:

On Wednesday 07 Nov 2007 1:57 am Kevin <[e-mail] in
article <[e-mail] .com>:

<snip>

printf("Locations: %u, %u\r\n", &test, &test1);

No. To print pointers use the '%p' specifier and cast the corresponding
argument to void *. Also the '\r' is not only not necessary but may
cause problems. The C Standard library translates a '\n' to whatever
the system uses as end-of-line.

very rarely explicit \r is needed when the system output doesn't
match the required output. I've even had to generate \r\r\n!
I suppose the output should have been binary rather than text.
I can't rememeber if it was.

<snip>

--
Nick Keighley

[santosh]

On Wednesday 07 Nov 2007 2:13 pm Nick Keighley
<ni******************@hotmail.comwrote in article
<11**********************@57g2000hsv.googlegroups. com>:

On 6 Nov, 20:46, santosh <[e-mail]:

>On Wednesday 07 Nov 2007 1:57 am Kevin <[e-mail]
in article <[e-mail] .com>:

<snip>

printf("Locations: %u, %u\r\n", &test, &test1);

No. To print pointers use the '%p' specifier and cast the
corresponding argument to void *. Also the '\r' is not only not
necessary but may cause problems. The C Standard library translates a
'\n' to whatever the system uses as end-of-line.

very rarely explicit \r is needed when the system output doesn't
match the required output. I've even had to generate \r\r\n!
I suppose the output should have been binary rather than text.
I can't rememeber if it was.

<snip>

Is such an implementation non-conforming as per the Standard?

[Charlie Gordon]

"santosh" <sa*********@gmail.coma écrit dans le message de news:
fg**********@registered.motzarella.org...

On Wednesday 07 Nov 2007 1:57 am Kevin <ke********@gmail.comwrote in
article <11**********************@i38g2000prf.googlegroups .com>:

>Hey, I was hoping someone out here might be able to clue me in on some
alignment issues I'm having. Hopefully I can explain this best
through code below. ACSign and MyACSign functions below get compiled
(gcc) into one library, where as the code that executes these
functions gets compiled into a seperate library. Calls to MyACSign
work fine, calls to the straight ACSign do not and I believe it is due
to alignment issues, but I can't pinpoint how. This <i>should</ihave
been very elementary. Any help is of course greatly appreciated,

- Kevin
Function Code:
************************************************* *******************
double ACSign ( double a) {
if (a 0.0)
return(1.0);

Both the parenthesis and the decimal point are unnecessary.

> else if (a < 0.0)
return(-1.0);

Similarly here.

>}

I'm amazed you noticed the extra parentheses and decimal points, and fail to
point at the much more major problem in ACSign: it does not return anything
if a is 0 ;-)
To properly account for negative zero, it should probably return a.

double ACSign(double a) {
return a < 0 ? -1 : a 0 ? 1 : a;
}

If we don't care about negative zeroes, ACSign should probably return an int
and can be made even more obscure:

int ACSign(double a) { return (a 0) - (a < 0); }

Any half decent compiler would have complained about the missing return if
configured properly. Indeed it is a shame that most of them don't complain
for such obvious bugs when invoked without extra flags.

--
Chqrlie.