Manual Reference Pages - leadz (3)

NAME

leadz(3f) - [FORTRAN:INTRINSIC:BIT INQUIRY] Number of leading zero bits of an integer

SYNTAX

result = leadz(i)

DESCRIPTION

LEADZ returns the number of leading zero bits of an integer.

ARGUMENTS

I Shall be of type INTEGER.

RETURN VALUE

The type of the return value is the same as a default INTEGER. If all the bits of I are zero, the result value is bit_size(i).

EXAMPLE

Sample program:

    program demo_leadz
    implicit none
    integer :: value, i
    character(len=80) :: f
      write(*,’(*(g0))’)’BIT_SIZE=’,bit_size(value)
      ! 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=0,bit_size(value)-1
         write (*,’("LEADING ZERO BITS=",i3,1x)’) leadz(value)
         write (*,’(" FOR VALUE ")’,advance=’no’)
         write(*,f,advance=’no’) value
         write(*,’(*(1x,g0))’) "OR",value
         value=value+2**(i)
      enddo
    end program demo_leadz

Results:

BIT_SIZE=32 LEADING ZERO BITS= 32 FOR VALUE 00000000000000000000000000000000 OR 0 LEADING ZERO BITS= 31 FOR VALUE 00000000000000000000000000000001 OR 1 LEADING ZERO BITS= 30 FOR VALUE 00000000000000000000000000000011 OR 3 LEADING ZERO BITS= 29 FOR VALUE 00000000000000000000000000000111 OR 7 LEADING ZERO BITS= 28 FOR VALUE 00000000000000000000000000001111 OR 15 LEADING ZERO BITS= 27 FOR VALUE 00000000000000000000000000011111 OR 31 LEADING ZERO BITS= 26 FOR VALUE 00000000000000000000000000111111 OR 63 LEADING ZERO BITS= 25 FOR VALUE 00000000000000000000000001111111 OR 127 LEADING ZERO BITS= 24 FOR VALUE 00000000000000000000000011111111 OR 255 LEADING ZERO BITS= 23 FOR VALUE 00000000000000000000000111111111 OR 511 LEADING ZERO BITS= 22 FOR VALUE 00000000000000000000001111111111 OR 1023 LEADING ZERO BITS= 21 FOR VALUE 00000000000000000000011111111111 OR 2047 LEADING ZERO BITS= 20 FOR VALUE 00000000000000000000111111111111 OR 4095 LEADING ZERO BITS= 19 FOR VALUE 00000000000000000001111111111111 OR 8191 LEADING ZERO BITS= 18 FOR VALUE 00000000000000000011111111111111 OR 16383 LEADING ZERO BITS= 17 FOR VALUE 00000000000000000111111111111111 OR 32767 LEADING ZERO BITS= 16 FOR VALUE 00000000000000001111111111111111 OR 65535 LEADING ZERO BITS= 15 FOR VALUE 00000000000000011111111111111111 OR 131071 LEADING ZERO BITS= 14 FOR VALUE 00000000000000111111111111111111 OR 262143 LEADING ZERO BITS= 13 FOR VALUE 00000000000001111111111111111111 OR 524287 LEADING ZERO BITS= 12 FOR VALUE 00000000000011111111111111111111 OR 1048575 LEADING ZERO BITS= 11 FOR VALUE 00000000000111111111111111111111 OR 2097151 LEADING ZERO BITS= 10 FOR VALUE 00000000001111111111111111111111 OR 4194303 LEADING ZERO BITS= 9 FOR VALUE 00000000011111111111111111111111 OR 8388607 LEADING ZERO BITS= 8 FOR VALUE 00000000111111111111111111111111 OR 16777215 LEADING ZERO BITS= 7 FOR VALUE 00000001111111111111111111111111 OR 33554431 LEADING ZERO BITS= 6 FOR VALUE 00000011111111111111111111111111 OR 67108863 LEADING ZERO BITS= 5 FOR VALUE 00000111111111111111111111111111 OR 134217727 LEADING ZERO BITS= 4 FOR VALUE 00001111111111111111111111111111 OR 268435455 LEADING ZERO BITS= 3 FOR VALUE 00011111111111111111111111111111 OR 536870911 LEADING ZERO BITS= 2 FOR VALUE 00111111111111111111111111111111 OR 1073741823 LEADING ZERO BITS= 1 FOR VALUE 01111111111111111111111111111111 OR 2147483647

STANDARD

[[Fortran 2008]] and later

CLASS

[[Elemental procedure|Elemental function]]

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