Manual Reference Pages - leadz (3fortran)

NAME

LEADZ(3) - [BIT:COUNT] Number of leading zero bits of an integer

SYNOPSIS

result = leadz(i)

         elemental integer function leadz(i)

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

CHARACTERISTICS

o I may be an integer of any kind.

o the return value is a default integer type.

DESCRIPTION

LEADZ(3) returns the number of leading zero bits of an integer.

OPTIONS

o I : integer to count the leading zero bits of.

RESULT

The number of leading zero bits, taking into account the kind of the input value. If all the bits of I are zero, the result value is BIT_SIZE(I).
The result may also be thought of as BIT_SIZE(I)-1-K where K is the position of the leftmost 1 bit in the input I. Positions are from 0 to bit-size(), with 0 at the right-most bit.

EXAMPLES

Sample program:

    program demo_leadz
    implicit none
    integer :: value, i
    character(len=80) :: f

      ! make a format statement for writing a value as a bit string
      write(f,’("(b",i0,".",i0,")")’)bit_size(value),bit_size(value)

      ! show output for various integer values
      value=0
      do i=-150, 150, 50
         value=i
         write (*,’("LEADING ZERO BITS=",i3)’,advance=’no’) leadz(value)
         write (*,’(" OF VALUE ")’,advance=’no’)
         write(*,f,advance=’no’) value
         write(*,’(*(1x,g0))’) "AKA",value
      enddo
      ! Notes:
      ! for two’s-complements programming environments a negative non-zero
      ! integer value will always start with a 1 and a positive value with 0
      ! as the first bit is the sign bit. Such platforms are very common.
    end program demo_leadz

Results:

LEADING ZERO BITS= 0 OF VALUE 11111111111111111111111101101010 AKA -150 LEADING ZERO BITS= 0 OF VALUE 11111111111111111111111110011100 AKA -100 LEADING ZERO BITS= 0 OF VALUE 11111111111111111111111111001110 AKA -50 LEADING ZERO BITS= 32 OF VALUE 00000000000000000000000000000000 AKA 0 LEADING ZERO BITS= 26 OF VALUE 00000000000000000000000000110010 AKA 50 LEADING ZERO BITS= 25 OF VALUE 00000000000000000000000001100100 AKA 100 LEADING ZERO BITS= 24 OF VALUE 00000000000000000000000010010110 AKA 150

STANDARD

Fortran 2008

o	I may be an integer of any kind.
o	the return value is a default integer type.