On Wed, 2019-01-23 at 20:09 +0100, Michal Sudolsky wrote:
> I am tempted to note that -1 is stored in 8-bit integer in exactly
> same way as 0xFF.
Hi,
I used the code below with gcc 8.1.1 with this result (the result will
make sense when the code is read):
[0] is -1; same:0/1/0 as signed:-1/255 as unsigned:4294967295/255 switch
match: s:1 u:0
[1] is 0; same:1/1/1 as signed:0/0 as unsigned:0/0 switch match: s:1 u:1
[2] is 1; same:1/1/1 as signed:1/1 as unsigned:1/1 switch match: s:1 u:1
[3] is 255; same:0/0/1 as signed:-1/255 as unsigned:4294967295/255 switch
match: s:0 u:1
what it should write is to have the 'same' triple all ones in at least
one column, not any of them zeros. You can see that 0xff and -1 are not
the same when it comes to comparison, either with a real enum value or
with signed and unsigned integers. I believe (according to my
experience) that enums are like *signed* integers. Thus one might be
careful what replacement type is used and which values will be assigned
to it.
The change mabri committed doesn't fix anything to upstream, it fixes a
thing only to Francesco's private (and modified) checkout. The change
also doesn't break anything upstream. Unless, some time later, someone
decides to make Unknown -1 or anything like that. Then, hopefully, the
compiler will claim something, thus it'll be noticed.
Bye,
zyx
The used code follows. It generates compiler warnings with the switch-
es, which is for good when looking for mistakes:
----------------------------------------------------
/* g++ test.cpp -o test && ./test */
#include <stdio.h>
typedef enum {
enMinusOne = -1,
enZero = 0,
enOne = 1,
enFF = 0xFF
} EN;
int
main (void)
{
signed char n_int8;
unsigned char n_uint8;
bool smatch, umatch;
int ii;
EN ens[4] = { enMinusOne, enZero, enOne, enFF };
for (ii = 0; ii < 4; ii++) {
n_int8 = ens[ii];
n_uint8 = ens[ii];
#define test_switch(_val,_res) \
switch (_val) { \
case enMinusOne: _res = ii == 0; break; \
case enZero: _res = ii == 1; break; \
case enOne: _res = ii == 2; break; \
case enFF: _res = ii == 3; break; \
default: _res = false; break; \
}
test_switch (n_int8, smatch);
test_switch (n_uint8, umatch);
#undef test_switch
printf ("[%d] is %d; same:%d/%d/%d as signed:%d/%d as
unsigned:%u/%u switch match: s:%d u:%d\n", ii, ens[ii],
n_int8 == n_uint8, n_int8 == ens[ii], n_uint8 ==
ens[ii],
n_int8, n_uint8, n_int8, n_uint8,
smatch, umatch);
}
return 0;
}
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