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繼this thread後，我想將一個單/雙精度實數「AA」轉換爲一個整數「II」來計算分佈式變量的校驗和。Fortran和MPI_Reduce如何處理整數溢出？
以下評論，我已經使用內在的'轉移'，並完全改寫這篇文章。下面是一個小Fortran模塊，可用於計算分佈式數組的校驗和，這取決於庫2DECOMP&FFT。該模塊似乎在我的工作站上工作（gfortran 4.9.2，openmpi 1.6.5,4個處理器）。任何意見/評論，可能會提高代碼的可移植性將不勝感激。關於可移植性的主要問題是：Fortran和MPI_reduce是否按照標準以相同的方式處理整數溢出？
module checksum
use MPI
use decomp_2d, only : mytype, nrank, &
xsize, ysize, zsize, &
transpose_x_to_y, transpose_y_to_z, &
transpose_z_to_y, transpose_y_to_x
implicit none
private ! Make everything private unless declared public
real(mytype), parameter :: xx=1.
integer, parameter, public :: chksum_size = size(transfer(xx,(/0,0/)))
integer, dimension(chksum_size) :: chkr1, chkr2, chkr3
logical, save :: chksum_is_working
! Temporary work variables/arrays
integer :: code
integer, dimension(chksum_size) :: tmprchk
public :: init_chksum, chksum, equal_chksum
contains
!
! Function to compute the checksum of a real 3D array var
!
function chksum(var,nx,ny,nz)
integer, intent(in) :: nx, ny, nz
real(mytype), dimension(nx,ny,nz), intent(in) :: var
integer, dimension(chksum_size) :: chksum
tmprchk = sum(transfer(var,(/0,0/)))
call MPI_ALLREDUCE(tmprchk,chksum,chksum_size,MPI_INTEGER,MPI_SUM,MPI_COMM_WORLD,code)
end function chksum
!
! Subroutine to make sure input arrays have the same checksum
! First/second/third array are in X/Y/Z pencil
! If switch is provided, reference array is var3.
! Otherwise, reference array is var1
!
subroutine equal_chksum(var1, var2, var3, switch)
real(mytype), dimension(xsize(1),xsize(2),xsize(3)), intent(inout) :: var1
real(mytype), dimension(ysize(1),ysize(2),ysize(3)), intent(inout) :: var2
real(mytype), dimension(zsize(1),zsize(2),zsize(3)), intent(inout) :: var3
logical, optional, intent(in) :: switch
if (chksum_is_working) then ! compute checksums
chkr1 = chksum(var1,xsize(1),xsize(2),xsize(3))
chkr2 = chksum(var2,ysize(1),ysize(2),ysize(3))
chkr3 = chksum(var3,zsize(1),zsize(2),zsize(3))
else ! generate checksums
chkr1 = 1
chkr2 = 2
chkr3 = 3
endif
if (present(switch)) then
if (any(chkr3.ne.chkr2)) call transpose_z_to_y(var3,var2)
if (any(chkr3.ne.chkr1)) call transpose_y_to_x(var2,var1)
else
if (any(chkr1.ne.chkr2)) call transpose_x_to_y(var1,var2)
if (any(chkr1.ne.chkr3)) call transpose_y_to_z(var2,var3)
endif
end subroutine equal_chksum
!
! Subroutine used to check we have a working checksum
!
subroutine init_chksum(var1,var2,var3)
real(mytype), dimension(xsize(1),xsize(2),xsize(3)), intent(out) :: var1
real(mytype), dimension(ysize(1),ysize(2),ysize(3)), intent(out) :: var2
real(mytype), dimension(zsize(1),zsize(2),zsize(3)), intent(out) :: var3
! Same random data inside all arrays
call random_number(var1)
call transpose_x_to_y(var1,var2)
call transpose_y_to_z(var2,var3)
! Compute checksums
chkr1 = chksum(var1,xsize(1),xsize(2),xsize(3))
chkr2 = chksum(var2,ysize(1),ysize(2),ysize(3))
chkr3 = chksum(var3,zsize(1),zsize(2),zsize(3))
! Check checksums
if (any(chkr1.ne.chkr2).or.any(chkr1.ne.chkr3)) then
chksum_is_working = .false.
if (nrank.eq.0) print *,'Checksums based on integer overflow do not work'
else
chksum_is_working = .true.
endif
end subroutine init_chksum
end module checksum
你是什麼意思的「演員」？你想使用相同的位模式而不是數值（例如'transfer'）？ – francescalus
@francescalus謝謝，我不知道轉讓，這正是我需要的。它是標準/便攜式嗎？ – user1824346
你應該明白* cast *這個詞是不明確的，你只需解釋你對一些代碼做了什麼。例如在C++中有reinterpret_cast，dynamic_cast，static_cast和更多http://stackoverflow.com/questions/332030/when-should-static-cast-dynamic-cast-const-cast-and-reinterpret-cast-be-used我們無法從水晶球上看出你的意思。 –