On Wed, May 19, 2021 at 02:32:02PM +0200, Tobias Burnus wrote:
> Regarding gfortran.dg/pr96711.f90:
>
> On my x86-64-gnu-linux, it PASSes.
> On our powerpc64le-linux-gnu it FAILS with
> 'STOP 3' (→ also scan-dump count) and 'STOP 4'.
>
> Contrary to PR96983's bug summary, I don't get an ICE.
>
>
> On powerpc64le-linux-gnu, the following condition evaluates true (→ 'STOP
> 3'):
>
> real(16) :: y ! 128bit REAL
> integer(16), parameter :: k2 = nint (2 / epsilon (y), kind(k2))
> integer(16), parameter :: m2 = 10384593717069655257060992658440192_16
> !2**113
> if (k2 /= m2) stop 3
>
> On x86_64-linux-gnu, k2 == m2 — but on powerpc64le-linux-gnu,
> k2 == 2**106 instead of 2**113.
>
> My solution is to permit also 2**106 besides 2**113.
>
> @PowerPC maintainers: Does this make sense? – It seems to work on our
> PowerPC
> but with all the new 'long double' changes, does it also work for you?
I do not understand Fortran well enough, could you explain what the code
is supposed to do?
> PR fortran/96983
> * gfortran.dg/pr96711.f90:
You're missing the actual entry here, fwiw.
> - integer(16), parameter :: m2 = 10384593717069655257060992658440192_16
> !2**113
> + integer(16), parameter :: m2 = 10384593717069655257060992658440192_16
> !2**113 ! Some systems like x86-64
> + integer(16), parameter :: m2a = 81129638414606681695789005144064_16
> !2**106 ! Some systems like PowerPC
If you use double-double ("ibm long double") a number is represented as
the sum of two double precision numbers, while if you use IEEE quad
precision floating point you get a 112-bit fraction (and a leading one).
The most significant of the two DP numbers is the whole rounded to DP.
The actual precision varies, it depends on various factors :-/
Segher
> integer(16), volatile :: m
> x = 2 / epsilon (x)
> y = 2 / epsilon (y)
> m = nint (x, kind(m))
> ! print *, m
> if (k1 /= m1) stop 1
> if (m /= m1) stop 2
> m = nint (y, kind(m))
> ! print *, m
> - if (k2 /= m2) stop 3
> - if (m /= m2) stop 4
> + if (k2 /= m2 .and. k2 /= m2a) stop 3
> + if (m /= m2 .and. m /= m2a) stop 4
> end program
