My only suggestion is that you dump the values as bits and see where they differ
Definitely worth a try, but it appears not to have helped much.
So .... I changed the original Inline::C script to:
use strict;
use warnings;
use Inline C => Config =>
BUILD_NOISY => 1,
USING => 'ParseRegExp',
#CLEAN_AFTER_BUILD => 0,
;
use Inline C => <<'EOC';
#include <stdio.h>
int foo(void) {
_Decimal64 d64 = 0.DD, neg_zero, pos_zero = 0.DD;
void *pd64 = &d64, *pneg_zero = &neg_zero, *ppos_zero = &pos_zero;
int i;
neg_zero = pos_zero * -1.DD;
d64 *= -1.DD;
if(d64 != pos_zero) printf("!= 0\n");
else printf("== 0\n");
if(d64 != neg_zero) printf("!= -0\n");
else printf("== -0\n");
for(i = 7; i >= 0; i--)
printf("%02X", ((unsigned char*)pd64)[i]);
printf("\n");
for(i = 7; i >= 0; i--)
printf("%02X", ((unsigned char*)pneg_zero)[i]);
printf("\n");
for(i = 7; i >= 0; i--)
printf("%02X", ((unsigned char*)ppos_zero)[i]);
printf("\n");
return 0;
}
EOC
foo();
It now outputs:
!= 0
== -0
B1C0000000000000
B1C0000000000000
31C0000000000000
"B1C000..." is a _Decimal64 -0, and "31C000..." a _Decimal64 0.
The first bit is the sign bit, the next 10 bits encode the exponent, and the 54-bit significand is an implicit 0 bit followed by the remaining 53 bits (all 0).
When I run that revised C code as a C program it outputs (correctly):
== 0
== -0
B1C0000000000000
B1C0000000000000
31C0000000000000
I also modified the Inline::C rendition that was getting it right to:
use strict;
use warnings;
use Inline C => Config =>
BUILD_NOISY => 1,
USING => 'ParseRegExp',
#CLEAN_AFTER_BUILD => 0,
;
use Inline C => <<'EOC';
#include <stdio.h>
void _is_zero(_Decimal64 d64) {
_Decimal64 neg_zero, pos_zero = 0.DD;
void *pd64 = &d64, *pneg_zero = &neg_zero, *ppos_zero = &pos_zero;
int i;
neg_zero = pos_zero * -1.DD;
if(d64 != pos_zero) printf("!= 0\n");
else printf("== 0\n");
if(d64 != neg_zero) printf("!= -0\n");
else printf("== -0\n");
for(i = 7; i >= 0; i--)
printf("%02X", ((unsigned char*)pd64)[i]);
printf("\n");
for(i = 7; i >= 0; i--)
printf("%02X", ((unsigned char*)pneg_zero)[i]);
printf("\n");
for(i = 7; i >= 0; i--)
printf("%02X", ((unsigned char*)ppos_zero)[i]);
printf("\n");
}
int foo(void) {
_Decimal64 d64 = 0.DD;
d64 *= -1.DD;
_is_zero(d64);
return 0;
}
EOC
foo();
It still outputs (correctly):
== 0
== -0
B1C0000000000000
B1C0000000000000
31C0000000000000
It's as though the
!= operation (in the problem script) believes that the values it's comparing are unsigned.
Cheers,
Rob
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