| Message ID | 20180511071052.1443-1-ptesarik@suse.com |
|---|---|
| State | New |
| Headers | show |
| Series | [1/1] Fix conversion from uint64 to float128 | expand |
On Fri, 11 May 2018 09:10:52 +0200 Petr Tesarik <ptesarik@suse.com> wrote: > The significand is passed to normalizeRoundAndPackFloat128() as high > first, low second. The current code passes the integer first, so the > result is incorrectly shifted left by 64 bits. > > This bug affects the emulation of s390x instruction CXLGBR (convert > from logical 64-bit binary-integer operand to extended BFP result). I forgot to add a simple reproducer: #include <stdio.h> #include <stdlib.h> int main(int argc, char **argv) { unsigned long long x = atoll(argv[1]); long double d = x; printf("%llu -> %Lf\n", x, d); return 0; } On a real s390x, I get this: linux-nig1:~ # ./cast 1 1 -> 1.000000 An s390x emulated with (unpatched) qemu-system-s390x gives: linux-2s2c:~ # ./cast 1 1 -> 18446744073709551616.000000 That is 2^64. Petr T
On 11 May 2018 at 08:10, Petr Tesarik <ptesarik@suse.com> wrote: > The significand is passed to normalizeRoundAndPackFloat128() as high > first, low second. The current code passes the integer first, so the > result is incorrectly shifted left by 64 bits. > > This bug affects the emulation of s390x instruction CXLGBR (convert > from logical 64-bit binary-integer operand to extended BFP result). > > Cc: qemu-stable@nongnu.org > Signed-off-by: Petr Tesarik <ptesarik@suse.com> > --- > fpu/softfloat.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fpu/softfloat.c b/fpu/softfloat.c > index 70e0c40a1c..386805475b 100644 > --- a/fpu/softfloat.c > +++ b/fpu/softfloat.c > @@ -3139,7 +3139,7 @@ float128 uint64_to_float128(uint64_t a, float_status *status) > if (a == 0) { > return float128_zero; > } > - return normalizeRoundAndPackFloat128(0, 0x406E, a, 0, status); > + return normalizeRoundAndPackFloat128(0, 0x406E, 0, a, status); > } Reviewed-by: Peter Maydell <peter.maydell@linaro.org> thanks -- PMM
On 05/11/2018 12:10 AM, Petr Tesarik wrote: > The significand is passed to normalizeRoundAndPackFloat128() as high > first, low second. The current code passes the integer first, so the > result is incorrectly shifted left by 64 bits. > > This bug affects the emulation of s390x instruction CXLGBR (convert > from logical 64-bit binary-integer operand to extended BFP result). > > Cc: qemu-stable@nongnu.org > Signed-off-by: Petr Tesarik <ptesarik@suse.com> > --- > fpu/softfloat.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Queued, thanks. r~
diff --git a/fpu/softfloat.c b/fpu/softfloat.c index 70e0c40a1c..386805475b 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -3139,7 +3139,7 @@ float128 uint64_to_float128(uint64_t a, float_status *status) if (a == 0) { return float128_zero; } - return normalizeRoundAndPackFloat128(0, 0x406E, a, 0, status); + return normalizeRoundAndPackFloat128(0, 0x406E, 0, a, status); }
The significand is passed to normalizeRoundAndPackFloat128() as high first, low second. The current code passes the integer first, so the result is incorrectly shifted left by 64 bits. This bug affects the emulation of s390x instruction CXLGBR (convert from logical 64-bit binary-integer operand to extended BFP result). Cc: qemu-stable@nongnu.org Signed-off-by: Petr Tesarik <ptesarik@suse.com> --- fpu/softfloat.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)