https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94981
Bug ID: 94981
Summary: Wrong casts on Power machines dealing with fctiwuz
instruction
Product: gcc
Version: 9.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: tony.reix at atos dot net
Target Milestone: ---
There are several issues dealing with GCC 8.30 and 9.3.0 (and also 10), for C
and C++, on AIX and Fedora/PPC64LE .
This appears when casting a float/double/long-double to an unsigned type, with
different cases.
This is related to the assembly instruction fctiwuz .
Here are 3 programs showing all the cases, with a reference to Fedora/x86_64.
Also, it looks like there are missing tests in GCC.
# cat double.c
#include <stdio.h>
int main()
{
double d = -2;
char c = (char)d;
signed char sc = (signed char)d;
printf("%d\n", (int)c);
printf("%d\n", (int)sc);
return 0;
}
# cat vector.cc
#include <vector>
#include <iostream>
double const dbl[4] = { 10, -1, -2, 4 };
int main()
{
double d = -2;
char c = (char)d;
std::cout << (int)c << std::endl;
std::vector<char> v(&dbl[0], &dbl[4]);
for (auto it = begin (v); it != end (v); ++it) {
std::cout << (int)*it << std::endl;
}
return 0;
}
Bug is same if "char" is replaced by "unsigned short" or "unsigned int".
So, the issue seems to appear on:
- AIX when converting a "double", a "float", or a long double" toward:
char, unsigned char, unsigned short, unsigned int, unsigned long
in 32-bit and 64-bit.
- Linux/Power when converting a "double" or a "float" toward an "unsigned"
type.
On AIX and Linux/Power.
double -2 --> char
float -2 --> char
C |
C++
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
| Default | -fsigned-char | -funsigned-char | Default |
-fsigned-char | -funsigned-char |
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
Fedora/x86_64 | signed | signed
|
9.3.1 20200408| -2 | -2 | 254 | -2 |
-2 | 254 |
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
Fedora/Power | signed, but: neg zeroed | signed, but:
neg zeroed |
9.3.1 20200408| 0 | -2 | 0 | 0 |
-2 | 0 | BUG
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
AIX | |
|
6.3.0 | unsigned | unsigned
|
| 254 | -2 | 254 | 254 |
-2 | 254 |
8.4.0 & 9.3.0 | signed, but: neg zeroed | signed, but:
neg zeroed |
| 0 | -2 | 0 | 0 |
-2 | 0 | BUG !!
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
long double -2 --> char
C |
C++
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
| Default | -fsigned-char | -funsigned-char | Default |
-fsigned-char | -funsigned-char |
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
Fedora/x86_64 | signed | signed
|
9.3.1 20200408| -2 | -2 | 254 | -2 |
-2 | 254 |
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
Fedora/Power | unsigned | unsigned
|
9.3.1 20200408| 254 | -2 | 254 | 254 |
-2 | 254 | BUG ??
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
AIX | |
|
6.3.0 | unsigned | unsigned
|
| 254 | -2 | 254 | 254 |
-2 | 254 |
8.4.0 & 9.3.0 | signed, but: neg zeroed | signed, but:
neg zeroed |
| 0 | -2 | 0 | 0 |
-2 | 0 | BUG !
--------------|-----------|---------------|-----------------|-----------|---------------|-----------------|
# cat cast.c
#include <stdio.h>
int main()
{
float f = -2;
double d = -2;
long double ld = -2;
char c;
unsigned char uc;
unsigned short us;
unsigned int ui;
unsigned long ul;
printf(" %5s %5s %5s %5s %5s\n", "c", "uc", "us", "ui",
"ul");
c = (char)f;
uc = (unsigned char)f;
us = (unsigned short)f;
ui = (unsigned int)f;
ul = (unsigned long)f;
printf("float: %5d %5d %5d %5d %5d\n", (int)c, (int)uc, (int)us,
(int)ui, (int)ul);
c = (char)d;
uc = (unsigned char)d;
us = (unsigned short)d;
ui = (unsigned int)d;
ul = (unsigned long)d;
printf("double: %5d %5d %5d %5d %5d\n", (int)c, (int)uc, (int)us,
(int)ui, (int)ul);
c = (char)ld;
uc = (unsigned char)ld;
us = (unsigned short)ld;
ui = (unsigned int)ld;
ul = (unsigned long)ld;
printf("long double: %5d %5d %5d %5d %5d\n", (int)c, (int)uc, (int)us,
(int)ui, (int)ul);
return 0;
}
Fedora/x86_64 : OK
c uc us ui ul
float: -2 254 65534 -2 -2
double: -2 254 65534 -2 -2
long double: -2 254 65534 -2 -2
Fedora/Power : KO
c uc us ui ul
float: 0 0 0 0 0
double: 0 0 0 0 0
long double: 254 254 65534 -2 0
AIX GCC 6.3.0 : OK
c uc us ui ul
float: 254 254 65534 -2 -2
double: 254 254 65534 -2 -2
long double: 254 254 65534 -2 -2
AIX GCC 8.4.0 & 9.3.0 32bit or 64bit : KO
c uc us ui ul
float: 0 0 0 0 0
double: 0 0 0 0 0
long double: 0 0 0 0 0
