Fortran 90の組み込み関数 `COUNT` の使用方法の確認

main.f08

! ==================================================================================================================================
! 
! # objective #
! Check how to use an intrinsic funcion: `count`
! 
! # reference #
! https://gcc.gnu.org/onlinedocs/gfortran/COUNT.html
! 
! # compiler version #
! gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04) 
! 
! ==================================================================================================================================

program main

    ! <module>s to import
    use, intrinsic :: iso_fortran_env


    ! require all variables to be explicitly declared
    implicit none


    ! constant(s) for this <program>
    integer(INT32) , parameter :: num_samples = 10_INT32 ** 8_INT32
    real(REAL64)   , parameter :: boundary    = 0.5_REAL64


    ! variable(s) for this <program>
    integer(INT32)               :: iter
    logical        , allocatable :: mask(:)
    integer(INT32)               :: retval_count_func
    integer(INT32)               :: retval_count_loop
    real(REAL64)   , allocatable :: sample(:)


    ! STEP.01
    ! allocate the array to store samples
    allocate( sample (num_samples) )
    allocate( mask   (num_samples) )


    ! STEP.02
    ! generate samples
    call random_number( harvest= sample(:) )


    ! STEP.03
    ! adjust the range of samples
    sample(:) = 2 * sample(:) - 1.0_REAL64


    ! STEP.04
    ! test the intrinsic function `count`
    mask(:)           = abs( sample(:) ) .le. boundary
    retval_count_func = count( mask= mask(:) )

    retval_count_loop = 0_INT32

    do iter = 1_INT32 , num_samples , 1_INT32
        if ( mask(iter) ) retval_count_loop = retval_count_loop + 1_INT32
    end do


    ! STEP.05
    ! show the result
    print *, 'total : ' , num_samples
    print *, 'func  : ' , retval_count_func
    print *, 'loop  : ' , retval_count_loop

end program main

! ==================================================================================================================================
! EOF
! ==================================================================================================================================

Makefile

FCFLAGS = -ffree-line-length-none -O2 -pedantic -std=f2008 -Wall -Wextra # -fbacktrace -fbounds-check 
OBJS    = ./main.o

main.exe: $(OBJS)
	gfortran $(FCFLAGS) -o ./main.exe $(OBJS)

%.o: %.f08
	gfortran $(FCFLAGS) -c $<

clean:
	rm ./*.mod ./*.o