get_hash_mod Module Reference

Functions/Subroutines
subroutine, public	get_hash (a, asize, hash, lreduce)
subroutine, private	bitsum (a, asize, hash, lreduce)

Function/Subroutine Documentation

bitsum()

subroutine, private get_hash_mod::bitsum ( real(r8), dimension(:), intent(in) a, integer, intent(in) asize, integer(i8b) hash, logical, intent(in), optional lreduce )

private

Definition at line 169 of file get_hash.F.

!***********************************************************************
!                                                                      !
!  Computes the checksum of a 1D floating-point by casting each value  !
!  to an integer to faciliate the invariant order of the sum in tiled  !
!  parallel applications. A real number can be represented with a set  !
!  64-bit integers (Hallberg and Adcroft, 2014).                       !
!                                                                      !
!  Reference:                                                          !
!                                                                      !
!    Hallberg, R. and A. Adcroft, 2014: An order-invariant real-to-    !
!      integer conversion sum, Parallel Computing, 40, 140-143,        !
!      doi:10.1016/j.parco.2014.04.007.                                !
!                                                                      !
!***********************************************************************
!
!  Imported variable declarations.
!
      logical, intent(in), optional :: Lreduce
!
      integer, intent(in) :: Asize
 
      integer(i8b) :: hash
!
      real(r8), intent(in) :: A(:)
!
!  Local variable declarations.
!
      integer, parameter :: Ak = kind(a)
      integer :: i, j
!
      integer(i8b) :: Ac, Asum
#if defined DISTRIBUTE && (defined JEDI || defined PIO_LIB)
      integer(i8b) :: ibuffer(1)
!
      character (len=3) :: op_handle(1)
#endif
!
!-----------------------------------------------------------------------
!  Compute checksum by counting bit-by-bit and summing.
!-----------------------------------------------------------------------
!
!  Here, the "POPCNT" function counts the number of set bits in a
!  machine instruction.  For example, for two 8-bit words operated
!  with XOR, we get
!
!    00100110
!    01100000
!   ----------
!    01000110
!
!    POPCNT(01000110) = 3       'counts the number of bits set to 1'
!
!  The POPCNT is available in all modern Fortran compilers and CPU
!  architectures.
!
      asum=0_i8b
      DO i=1,asize
        ac=popcnt(transfer(abs(a(i)), 1_ak))
        asum=asum+ac
      END DO
      hash=asum
 
#if defined DISTRIBUTE && (defined JEDI || defined PIO_LIB)
!
!  If PIO library data processing, sum across all processes. Recall that
!  one or several PETs are reading and or writing data, so we need a
!  global reduction of the checksum, which is order invariant for parallel
!  tiles. The integer arithmetic has no truncation errors. Notice that
!  such reduction is not required in I/0 processed by the master node
!  and Lreduce=.FALSE in such cases.
!
      IF (PRESENT(lreduce)) THEN
        IF (lreduce) THEN
          ibuffer(1)=asum
          op_handle(1)='SUM'
          CALL mp_reduce (1, 1, 1, ibuffer, op_handle)
          hash=ibuffer(1)
        END IF
      END IF
#endif
!
      RETURN

Referenced by get_hash().

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get_hash()

subroutine, public get_hash_mod::get_hash	(	real(r8), dimension(:), intent(in)	a,
		integer, intent(in)	asize,
		integer(i8b), intent(out)	hash,
		logical, intent(in), optional	lreduce )

Definition at line 71 of file get_hash.F.

!***********************************************************************
!
!
!  Imported variable declarations.
!
      logical, intent(in), optional :: Lreduce
!
      integer, intent(in) :: Asize
      integer(i8b), intent(out) :: hash
!
      real(r8), intent(in) :: A(:)
!
!  Local variable declarations.
!
      logical, save :: first = .true.
!
!-----------------------------------------------------------------------
!  Compute checksum for the requested floating point vector.
!-----------------------------------------------------------------------
!
      hash=0_i8b
!
      SELECT CASE (uppercase(trim(hashmethod)))
#ifdef ADLER32_CHECKSUM
        CASE ('ADLER32')
          CALL adler32 (a, asize, hash)
#endif
        CASE ('BITSUM')
          CALL bitsum (a, asize, hash, lreduce)
#ifdef CRC32_CHECKSUM
        CASE ('CRC32')
          IF (first) THEN
            first=.false.
            CALL crc32_ini                  ! compute CRC-32 look table
          END IF
          CALL crc32 (a, asize, hash)
#endif
        CASE DEFAULT
          WRITE (stdout,10) trim(hashmethod)
          exit_flag=5
      END SELECT
!
  10  FORMAT (/,' GET_HASH - Illegal checksum method: ',a)
!
      RETURN

References bitsum(), mod_scalars::exit_flag, mod_scalars::hashmethod, mod_iounits::stdout, and strings_mod::uppercase().

Referenced by get_ngfld_nf90(), get_ngfld_pio(), get_ngfldr_nf90(), get_ngfldr_pio(), nf_fread2d_mod::nf_fread2d::nf90_fread2d(), nf_fread2d_bry_mod::nf_fread2d_bry::nf90_fread2d_bry(), nf_fread3d_mod::nf_fread3d::nf90_fread3d(), nf_fread3d_bry_mod::nf_fread3d_bry::nf90_fread3d_bry(), nf_fread4d_mod::nf_fread4d::nf90_fread4d(), nf_fread2d_mod::nf_fread2d::pio_fread2d(), nf_fread2d_bry_mod::nf_fread2d_bry::pio_fread2d_bry(), nf_fread3d_mod::nf_fread3d::pio_fread3d(), nf_fread3d_bry_mod::nf_fread3d_bry::pio_fread3d_bry(), nf_fread4d_mod::nf_fread4d::pio_fread4d(), stats_mod::stats_2dfld(), stats_mod::stats_3dfld(), and stats_mod::stats_4dfld().

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