rdieee.f

计算线性趋势 回归系数 主要用于气象站点值的线性趋势计算

      subroutine rdieee(rieee,a,num)
!$$$  SUBPROGRAM DOCUMENTATION BLOCK
!                .      .    .                                       .
! SUBPROGRAM:    rdieee 
!   PRGMMR: Gilbert         ORG: W/NP11    DATE: 2000-05-09
!
! ABSTRACT: This subroutine reads a list of real values in 
!   32-bit IEEE floating point format.
!
! PROGRAM HISTORY LOG:
! 2000-05-09  Gilbert
!
! USAGE:    CALL rdieee(rieee,a,num)
!   INPUT ARGUMENT LIST:
!     rieee    - Input array of floating point values in 32-bit IEEE format.
!     num      - Number of floating point values to convert.
!
!   OUTPUT ARGUMENT LIST:      
!     a        - Output array of real values.
!
! REMARKS: None
!
! ATTRIBUTES:
!   LANGUAGE: Fortran 90
!   MACHINE:  IBM SP
!
!$$$

      real(4),intent(in) :: rieee(num)
      real,intent(out) :: a(num)
      integer,intent(in) :: num

      integer(4) :: ieee

      real,save :: two23
      real,save :: two126
      integer,save :: once=0

      if ( once .EQ. 0 ) then
         once=1
         two23=scale(1.0,-23)
         two126=scale(1.0,-126)
      endif

      do j=1,num
!
!  Transfer IEEE bit string to integer variable
!
        ieee=transfer(rieee(j),ieee)
!
!  Extract sign bit, exponent, and mantissa
!
        isign=ibits(ieee,31,1)
        iexp=ibits(ieee,23,8)
        imant=ibits(ieee,0,23)
        sign=1.0
        if (isign.eq.1) sign=-1.0
        
        if ( (iexp.gt.0).and.(iexp.lt.255) ) then
          temp=2.0**(iexp-127)
          a(j)=sign*temp*(1.0+(two23*real(imant)))

        elseif ( iexp.eq.0 ) then
          if ( imant.ne.0 ) then
            a(j)=sign*two126*two23*real(imant)
          else
            a(j)=sign*0.0
          endif

        elseif ( iexp.eq.255 ) then
          a(j)=sign*huge(a(j))

        endif

      enddo

      return
      end