On 23.03.22 17:26, Thomas Huth wrote: > Reported by Paul Eggert in > https://lists.gnu.org/archive/html/bug-gnulib/2021-09/msg00050.html > > This program currently prints different results when run with TCG instead > of running on real s390x hardware: > > #include <stdio.h> > > int overflow_32 (int x, int y) > { > int sum; > return __builtin_sub_overflow (x, y, &sum); > } > > int overflow_64 (long long x, long long y) > { > long sum; > return __builtin_sub_overflow (x, y, &sum); > } > > int a1 = 0; > int b1 = -2147483648; > long long a2 = 0L; > long long b2 = -9223372036854775808L; > > int main () > { > { > int a = a1; > int b = b1; > printf ("a = 0x%x, b = 0x%x\n", a, b); > printf ("no_overflow = %d\n", ! overflow_32 (a, b)); > } > { > long long a = a2; > long long b = b2; > printf ("a = 0x%llx, b = 0x%llx\n", a, b); > printf ("no_overflow = %d\n", ! overflow_64 (a, b)); > } > } > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/618 > Suggested-by: Bruno Haible <br...@clisp.org> > Signed-off-by: Thomas Huth <th...@redhat.com> > --- > target/s390x/tcg/cc_helper.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/target/s390x/tcg/cc_helper.c b/target/s390x/tcg/cc_helper.c > index e11cdb745d..b2e8d3d9f5 100644 > --- a/target/s390x/tcg/cc_helper.c > +++ b/target/s390x/tcg/cc_helper.c > @@ -151,7 +151,7 @@ static uint32_t cc_calc_add_64(int64_t a1, int64_t a2, > int64_t ar) > > static uint32_t cc_calc_sub_64(int64_t a1, int64_t a2, int64_t ar) > { > - if ((a1 > 0 && a2 < 0 && ar < 0) || (a1 < 0 && a2 > 0 && ar > 0)) { > + if ((a1 >= 0 && a2 < 0 && ar < 0) || (a1 < 0 && a2 > 0 && ar > 0)) { > return 3; /* overflow */ > } else { > if (ar < 0) { > @@ -211,7 +211,7 @@ static uint32_t cc_calc_add_32(int32_t a1, int32_t a2, > int32_t ar) > > static uint32_t cc_calc_sub_32(int32_t a1, int32_t a2, int32_t ar) > { > - if ((a1 > 0 && a2 < 0 && ar < 0) || (a1 < 0 && a2 > 0 && ar > 0)) { > + if ((a1 >= 0 && a2 < 0 && ar < 0) || (a1 < 0 && a2 > 0 && ar > 0)) { > return 3; /* overflow */ > } else { > if (ar < 0) {
Again, intuitively I'd check for a) Subtracting a negative number from a positive one -> Adding two positive numbers should result in the result being bigger than the first parameter. a1 > 0 && a2 < 0 && ar < a1 a) Subtracting a positive number from a negative one -> Adding two negative numbers should result in something that's smaller than the first parameter a1 < 0 && a2 > 0 && ar > a1 But maybe I am missing something :) -- Thanks, David / dhildenb
