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Manual Reference Pages  - shifta (3fortran)

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NAME

SHIFTA(3) - [BIT:SHIFT] Right shift with fill

SYNOPSIS

result = shifta(i, shift )

         elemental integer(kind=KIND) function shifta(i, shift)

          integer(kind=KIND),intent(in) :: i
          integer(kind=**),intent(in) :: shift

CHARACTERISTICS

o	a kind designated as ** may be any supported kind for the type
o	I is an integer of any kind
o	SHIFT is an integer of any kind
o	the result will automatically be of the same type, kind and rank as I.

DESCRIPTION

SHIFTA(3) returns a value corresponding to I with all of the bits shifted right by SHIFT places and the vacated bits on the left filled with the value of the original left-most bit.

OPTIONS

o	I : The initial value to shift and fill
o	SHIFT : how many bits to shift right. It shall be nonnegative and less than or equal to BIT_SIZE(I). or the value is undefined. If SHIFT is zero the result is I.

RESULT

The result has the value obtained by shifting the bits of I to the right SHIFT bits and replicating the leftmost bit of I in the left SHIFT bits (Note the leftmost bit in "two’s complement" representation is the sign bit).

Bits shifted out from the right end are lost.

If SHIFT is zero the result is I.

EXAMPLES

Sample program:

    program demo_shifta
    use,intrinsic :: iso_fortran_env, only : int8, int16, int32, int64
    implicit none
    integer(kind=int32) :: ival
    integer             :: shift
    integer(kind=int32) :: oval
    integer(kind=int32),allocatable :: ivals(:)
    integer             :: i
    integer(kind=int8)  :: arr(2,2)=reshape([2,4,8,16],[2,2])

      ! basic usage
      write(*,*)shifta(100,3)

      ! loop through some interesting values
       shift=5

       ivals=[ -1, -0, +0, +1, &
       & int(b"01010101010101010101010101010101"), &
       & int(b"10101010101010101010101010101010"), &
       & int(b"00000000000000000000000000011111") ]

       ! does your platform distinguish between +0 and -0?
       ! note the original leftmost bit is used to fill in the vacated bits

       write(*,’(/,"SHIFT =  ",i0)’) shift
       do i=1,size(ivals)
          ival=ivals(i)
          write(*,’(  "I =      ",b32.32," == ",i0)’) ival,ival
          oval=shifta(ival,shift)
          write(*,’(  "RESULT = ",b32.32," == ",i0)’) oval,oval
       enddo
       ! elemental
       write(*,*)"characteristics of the result are the same as input"
       write(*,’(*(g0,1x))’) &
         & "kind=",kind(shifta(arr,3)), "shape=",shape(shifta(arr,3)), &
         & "size=",size(shifta(arr,3)) !, "rank=",rank(shifta(arr,3))

    end program demo_shifta

Results:

     >           12
     >
     > SHIFT =  5
     > I =      11111111111111111111111111111111 == -1
     > RESULT = 11111111111111111111111111111111 == -1
     > I =      00000000000000000000000000000000 == 0
     > RESULT = 00000000000000000000000000000000 == 0
     > I =      00000000000000000000000000000000 == 0
     > RESULT = 00000000000000000000000000000000 == 0
     > I =      00000000000000000000000000000001 == 1
     > RESULT = 00000000000000000000000000000000 == 0
     > I =      01010101010101010101010101010101 == 1431655765
     > RESULT = 00000010101010101010101010101010 == 44739242
     > I =      10101010101010101010101010101010 == -1431655766
     > RESULT = 11111101010101010101010101010101 == -44739243
     > I =      00000000000000000000000000011111 == 31
     > RESULT = 00000000000000000000000000000000 == 0
     >  characteristics of the result are the same as input
     > kind= 1 shape= 2 2 size= 4

STANDARD

Fortran 2008

SEE ALSO

SHIFTL(3), SHIFTR(3), ISHFT(3), ISHFTC(3)

fortran-lang intrinsic descriptions (license: MIT) @urbanjost

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Nemo Release 3.1

shifta (3fortran)

April 28, 2024

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