Manual Reference Pages - btest (3fortran)

NAME

BTEST(3) - [BIT:INQUIRY] Tests a bit of an integer value.

SYNOPSIS

result = btest(i,pos)

         elemental logical function btest(i,pos)

          integer(kind=**),intent(in)  :: i
          integer(kind=**),intent(in)  :: pos

CHARACTERISTICS

o I is an integer of any kind

o POS is a integer of any kind

o the result is a default logical

DESCRIPTION

BTEST(3) returns logical .true. if the bit at POS in I is set to 1. Position zero is the right-most bit. Bit position increases from right to left up to BITSIZE(I)-1.

OPTIONS

o I : The integer containing the bit to be tested

o POS : The position of the bit to query. it must be a valid position for the value I; ie. 0 <= POS <= BIT_SIZE(I).

RESULT

The result is a logical that has the value .true. if bit position POS of I has the value 1 and the value .false. if bit POS of I has the value 0.
Positions of bits in the sequence are numbered from right to left, with the position of the rightmost bit being zero.

EXAMPLES

Sample program:

    program demo_btest
    implicit none
    integer :: i, j, pos, a(2,2)
    logical :: bool
    character(len=*),parameter :: g=’(*(g0))’

         i = 32768 + 1024 + 64
        write(*,’(a,i0,"=>",b32.32,/)’)’Looking at the integer: ’,i

        ! looking one bit at a time from LOW BIT TO HIGH BIT
        write(*,g)’from bit 0 to bit ’,bit_size(i),’==>’
        do pos=0,bit_size(i)-1
            bool = btest(i, pos)
            write(*,’(l1)’,advance=’no’)bool
        enddo
        write(*,*)

        ! a binary format the hard way.
        ! Note going from bit_size(i) to zero.
        write(*,*)
        write(*,g)’so for ’,i,’ with a bit size of ’,bit_size(i)
        write(*,’(b32.32)’)i
        write(*,g)merge(’^’,’_’,[(btest(i,j),j=bit_size(i)-1,0,-1)])
        write(*,*)
        write(*,g)’and for ’,-i,’ with a bit size of ’,bit_size(i)
        write(*,’(b32.32)’)-i
        write(*,g)merge(’^’,’_’,[(btest(-i,j),j=bit_size(i)-1,0,-1)])

        ! elemental:
        !
        a(1,:)=[ 1, 2 ]
        a(2,:)=[ 3, 4 ]
        write(*,*)
        write(*,’(a,/,*(i2,1x,i2,/))’)’given the array a ...’,a
        ! the second bit of all the values in a
        write(*,’(a,/,*(l2,1x,l2,/))’)’the value of btest (a, 2)’,btest(a,2)
        ! bits 1,2,3,4 of the value 2
        write(*,’(a,/,*(l2,1x,l2,/))’)’the value of btest (2, a)’,btest(2,a)
    end program demo_btest

Results:

      > Looking at the integer: 33856=>11111111111111110111101111000000
      >
      > 00000000000000001000010001000000
      > 11111111111111110111101111000000
      > 1000010001000000
      > 11111111111111110111101111000000
      > from bit 0 to bit 32==>
      > FFFFFFTFFFTFFFFTFFFFFFFFFFFFFFFF
      >
      > so for 33856 with a bit size of 32
      > 00000000000000001000010001000000
      > ________________^____^___^______
      >
      > and for -33856 with a bit size of 32
      > 11111111111111110111101111000000
      > ^^^^^^^^^^^^^^^^_^^^^_^^^^______
      >
      > given the array a ...
      >  1  3
      >  2  4
      >
      > the value of btest (a, 2)
      >  F  F
      >  F  T
      >
      > the value of btest (2, a)
      >  T  F
      >  F  F

STANDARD

Fortran 95

o	I is an integer of any kind
o	POS is a integer of any kind
o	the result is a default logical

o	I : The integer containing the bit to be tested
o	POS : The position of the bit to query. it must be a valid position for the value I; ie. 0 <= POS <= BIT_SIZE(I).

Manual Reference Pages - btest (3fortran)

NAME

SYNOPSIS

CHARACTERISTICS

DESCRIPTION

OPTIONS

RESULT

EXAMPLES

STANDARD

SEE ALSO