https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128624
Bug ID: 128624
Summary: wrong code at -O0: (unsigned)(_Decimal64)2147483648
gives 0 (libbid sentinel 0x80000000 is also a valid
result)
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Keywords: dfp, wrong-code
Severity: normal
Priority: P3
Component: libgcc
Assignee: unassigned at gcc dot gnu.org
Reporter: jeffchen006 at gmail dot com
Target Milestone: ---
int printf(const char *, ...);
int main(void) {
_Decimal64 d = 2147483648.DD;
printf("%u\n", (unsigned)d);
}
$ gcc -O0 t.c && ./a.out
0
$ gcc -O1 t.c && ./a.out
2147483648
Expected: 2147483648. 2^31 is exact in _Decimal64 and fits in unsigned int, so
the result must be 2147483648. -O1 folds the conversion at compile time and is
correct. -O0 calls __bid_fixunsddsi, which is wrong.
Suspected cause: libgcc/config/libbid/_dd_to_usi.c, _td_to_usi.c, _sd_to_usi.c:
"if (res == 0x80000000) res = 0;". The invalid sentinel is equal to the valid
result 2^31. The _to_udi.c files have the same problem with 0x8000000000000000
((unsigned long long)(_Decimal128)9223372036854775808 gives 0). Code is from
the 2007 libbid import (200359e888d).
Known to fail: 8.5.0, 10.5.0, 11.4.0, 12.5.0, 13.4.0, 14.3.0, 15.2.0, 16.2.0,
17.0.
-O0 -fsanitize=undefined,address is clean.
gcc version 17.0.0 20261111 (experimental) (a2a11abfad3), x86_64-pc-linux-gnu
Configured with: --enable-languages=c,c++ --disable-multilib
--disable-bootstrap --enable-checking=release
