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继this thread后，我想将一个单/双精度实数“AA”转换为一个整数“II”来计算分布式变量的校验和。Fortran和MPI_Reduce如何处理整数溢出？
以下评论，我已经使用内在的'转移'，并完全改写这篇文章。下面是一个小Fortran模块，可用于计算分布式数组的校验和，这取决于库2DECOMP&FFT。该模块似乎在我的工作站上工作（gfortran 4.9.2，openmpi 1.6.5,4个处理器）。任何意见/评论，可能会提高代码的可移植性将不胜感激。关于可移植性的主要问题是：Fortran和MPI_reduce是否按照标准以相同的方式处理整数溢出？
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
你是什么意思的“演员”？你想使用相同的位模式而不是数值（例如'transfer'）？ – francescalus
@francescalus谢谢，我不知道转让，这正是我需要的。它是标准/便携式吗？ – user1824346
你应该明白* cast *这个词是不明确的，你只需解释你对一些代码做了什么。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我们无法从水晶球上看出你的意思。 –