Rounding on PowerPC with KIND=16

[Jerry DeLisle]

On 02/13/2015 01:11 PM, Jerry DeLisle wrote:
> If you run this program on x86-64 vs Power PC, the Power PC appears to have an
> off by one spacing.  I assume this means the least significant bit is off or we
> are converting wrong when we write it.  I suspect this is a known issue, but was
> wondering if anyone has explored it?  Could it have something to do with endianess?
>
> Jerry
>
> program testit
> use ISO_FORTRAN_ENV
>    implicit none
>    integer, parameter :: np = 16
>    character(50) :: astring
>    integer :: i, l, n
>    real(kind=np) :: r, s, t, u
>
>    r = 1.0_np
>    s = 10.0_np
>    t = r/s
>    u = (t + spacing(t)) * s
>
>    print "(g0)", r
>    print "(g0)", s
>    print "(g0)", t
>    print "(g0)", u
>    print "(g0)", t + spacing(t)
>    print "(g0)", t - spacing(t)
>    write(astring, "(g0)"), t
>    print *, len(trim(astring)), "   ", trim(astring)
>
> end program
>

Sample Output

x86-64:

1.00000000000000000000000000000000000
10.0000000000000000000000000000000000
.100000000000000000000000000000000005
1.00000000000000000000000000000000019
.100000000000000000000000000000000017
.999999999999999999999999999999999928E-0001
           37    .100000000000000000000000000000000005

PowerPC

1.00000000000000000000000000000000000
10.0000000000000000000000000000000000
.999999999999999999999999999999996919E-0001
1.00000000000000000000000000000000000
.100000000000000000000000000000001233
.999999999999999999999999999999981511E-0001
           43    .999999999999999999999999999999996919E-0001