Re: status of quadruple precision arithmetic in g95 and gfortran?

Herman D. Knoble <SkipKnobleLESS@xxxxxxxxxxxxxxx> wrote in
news:4dni22t33u3i6u6ctruig5iltu9he5d6im@xxxxxxx:

You are right about the cost of QP. Skip Knoble

Program Qtime
! Sample Program to illustrate DP versus QP compute times:
! Intel Fortran V9.0-5748 on AMD Opteron 852 with O2.

integer, parameter :: QDP = selected_real_kind(30)
real(kind=QDP) :: x, sum
real :: T1,T2, Seconds
integer :: i, pulses, PPS

x=1.5_QDP
sum=0.0_QDP
CALL SYSTEM_CLOCK(COUNT=Pulses,COUNT_RATE=PPS)
T1 = REAL(Pulses,QDP)/PPS

Do I=1,100000000
sum=sum+I*x
end do

CALL SYSTEM_CLOCK(COUNT=Pulses,COUNT_RATE=PPS)
T2 = REAL(Pulses,QDP)/PPS
Seconds=T2-T1
print *, " Time in seconds: ",Seconds
print *, "QDP=",QDP
print *, "Sum=",Sum

end Program Qtime


Output for: integer, parameter :: QDP = selected_real_kind(15)

Time in seconds: 0.5800781
QDP= 8
Sum= 7.500000080627340E+015


Why doesn't double precision produce a better result here?


Output for: integer, parameter :: QDP = selected_real_kind(30)
Time in seconds: 5.750000
QDP= 16
Sum= 7500000075000000.00000000000000000

On Tue, 28 Mar 2006 14:20:04 GMT, Tim Prince
<tprince@xxxxxxxxxxxxxxxxxx> wrote:

-|Bernhard Enders wrote:

<snip>

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