On Fri, 10 Sep 2021, Patrick Northon via Mingw-w64-public wrote:
Finally, here's the patch to change double formatting in hexadecimal. As you
can see, I managed to find a way to fix it with little changes. Only a few
minor adjustments needed.
Awesome! I appreciate that you managed to reuse the whole formatting
function as is.
In trying out a couple different cases comparing them to glibc, I spotted
one difference, reproducible with this snippet:
union {
double f;
uint64_t i;
} u = { .i = 0x0008000000000000ULL };
printf("%a\n", u.f);
printf("%.0a\n", u.f);
With your implementation, this prints:
0x0.8p-1022
0x1p-1022
However with glibc, this prints:
0x0.8p-1022
0x0p-1022
This looks wrong to me though, and I'd say your version is correct.
Surprisingly though, UCRT also prints the same here. As those probably
don't share the implementation, it would imply that there's some reason
for it (that I don't see).
On macOS, this case prints
0x1p-1023
0x1p-1023
which is another correct way of handling it (although different from how
glibc handles denormals).
// Martin
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