intrinsic.texi

理解和实践操作系统的一本好书

@code{BESYN(N, X)} computes the Bessel function of the second kind of order
@var{N} of @var{X}.

If both arguments are arrays, their ranks and shapes shall conform.

@item @emph{Standard}:
GNU extension

@item @emph{Class}:
Elemental function

@item @emph{Syntax}:
@code{RESULT = BESYN(N, X)}

@item @emph{Arguments}:
@multitable @columnfractions .15 .70
@item @var{N} @tab Shall be a scalar or an array of type  @code{INTEGER(*)}.
@item @var{X} @tab Shall be a scalar or an array of type  @code{REAL(*)}.
@end multitable

@item @emph{Return value}:
The return value is a scalar of type @code{REAL(*)}.

@item @emph{Example}:
@smallexample
program test_besyn
  real(8) :: x = 1.0_8
  x = besyn(5,x)
end program test_besyn
@end smallexample

@item @emph{Specific names}:
@multitable @columnfractions .20 .20 .20 .25
@item Name               @tab Argument            @tab Return type     @tab Standard
@item @code{DBESYN(N,X)} @tab @code{INTEGER(*) N} @tab @code{REAL(8)}  @tab GNU extension
@item                    @tab @code{REAL(8)    X} @tab                 @tab 
@end multitable
@end table



@node BIT_SIZE
@section @code{BIT_SIZE} --- Bit size inquiry function
@fnindex BIT_SIZE
@cindex bits, number of
@cindex size of a variable, in bits

@table @asis
@item @emph{Description}:
@code{BIT_SIZE(I)} returns the number of bits (integer precision plus sign bit)
represented by the type of @var{I}.

@item @emph{Standard}:
F95 and later

@item @emph{Class}:
Inquiry function

@item @emph{Syntax}:
@code{RESULT = BIT_SIZE(I)}

@item @emph{Arguments}:
@multitable @columnfractions .15 .70
@item @var{I} @tab The type shall be @code{INTEGER(*)}.
@end multitable

@item @emph{Return value}:
The return value is of type @code{INTEGER(*)}

@item @emph{Example}:
@smallexample
program test_bit_size
    integer :: i = 123
    integer :: size
    size = bit_size(i)
    print *, size
end program test_bit_size
@end smallexample
@end table



@node BTEST
@section @code{BTEST} --- Bit test function
@fnindex BTEST
@cindex bits, testing

@table @asis
@item @emph{Description}:
@code{BTEST(I,POS)} returns logical @code{.TRUE.} if the bit at @var{POS}
in @var{I} is set.

@item @emph{Standard}:
F95 and later

@item @emph{Class}:
Elemental function

@item @emph{Syntax}:
@code{RESULT = BTEST(I, POS)}

@item @emph{Arguments}:
@multitable @columnfractions .15 .70
@item @var{I} @tab The type shall be @code{INTEGER(*)}.
@item @var{POS} @tab The type shall be @code{INTEGER(*)}.
@end multitable

@item @emph{Return value}:
The return value is of type @code{LOGICAL}

@item @emph{Example}:
@smallexample
program test_btest
    integer :: i = 32768 + 1024 + 64
    integer :: pos
    logical :: bool
    do pos=0,16
        bool = btest(i, pos) 
        print *, pos, bool
    end do
end program test_btest
@end smallexample
@end table


@node C_ASSOCIATED
@section @code{C_ASSOCIATED} --- Status of a C pointer
@fnindex C_ASSOCIATED
@cindex association status, C pointer
@cindex pointer, C association status

@table @asis
@item @emph{Description}:
@code{C_ASSOICATED(c_prt1[, c_ptr2])} determines the status of the C pointer @var{c_ptr1}
or if @var{c_ptr1} is associated with the target @var{c_ptr2}.

@item @emph{Standard}:
F2003 and later

@item @emph{Class}:
Inquiry function

@item @emph{Syntax}:
@code{RESULT = C_ASSOICATED(c_prt1[, c_ptr2])}

@item @emph{Arguments}:
@multitable @columnfractions .15 .70
@item @var{c_ptr1} @tab Scalar of the type @code{C_PTR} or @code{C_FUNPTR}.
@item @var{c_ptr2} @tab (Optional) Scalar of the same type as @var{c_ptr1}.
@end multitable

@item @emph{Return value}:
The return value is of type @code{LOGICAL}; it is @code{.false.} if either
@var{c_ptr1} is a C NULL pointer or if @var{c_ptr1} and @var{c_ptr2}
point to different addresses.

@item @emph{Example}:
@smallexample
subroutine association_test(a,b)
  use iso_c_binding, only: c_associated, c_loc, c_ptr
  implicit none
  real, pointer :: a
  type(c_ptr) :: b
  if(c_associated(b, c_loc(a))) &
     stop 'b and a do not point to same target'
end subroutine association_test
@end smallexample

@item @emph{See also}:
@ref{C_LOC}, @ref{C_FUNLOC}
@end table


@node C_FUNLOC
@section @code{C_FUNLOC} --- Obtain the C address of a procedure
@fnindex C_FUNLOC
@cindex pointer, C address of procedures

@table @asis
@item @emph{Description}:
@code{C_FUNLOC(x)} determines the C address of the argument.

@item @emph{Standard}:
F2003 and later

@item @emph{Class}:
Inquiry function

@item @emph{Syntax}:
@code{RESULT = C_FUNLOC(x)}

@item @emph{Arguments}:
@multitable @columnfractions .15 .70
@item @var{x} @tab Interoperable function or pointer to such function.
@end multitable

@item @emph{Return value}:
The return value is of type @code{C_FUNPTR} and contains the C address
of the argument.

@item @emph{Example}:
@smallexample
module x
  use iso_c_binding
  implicit none
contains
  subroutine sub(a) bind(c)
    real(c_float) :: a
    a = sqrt(a)+5.0
  end subroutine sub
end module x
program main
  use iso_c_binding
  use x
  implicit none
  interface
    subroutine my_routine(p) bind(c,name='myC_func')
      import :: c_funptr
      type(c_funptr), intent(in) :: p
    end subroutine
  end interface
  call my_routine(c_funloc(sub))
end program main
@end smallexample

@item @emph{See also}:
@ref{C_ASSOCIATED}, @ref{C_LOC}, @ref{C_F_POINTER}, @ref{C_F_PROCPOINTER}
@end table


@node C_F_PROCPOINTER
@section @code{C_F_PROCPOINTER} --- Convert C into Fortran procedure pointer
@fnindex C_F_PROCPOINTER
@cindex pointer, C address of pointers

@table @asis
@item @emph{Description}:
@code{C_F_PROCPOINTER(cptr, fptr)} Assign the target of the C function pointer
@var{cptr} to the Fortran procedure pointer @var{fptr}.

Note: Due to the currently lacking support of procedure pointers in GNU Fortran
this function is not fully operable.

@item @emph{Standard}:
F2003 and later

@item @emph{Class}:
Subroutine

@item @emph{Syntax}:
@code{CALL C_F_PROCPOINTER(cptr, fptr)}

@item @emph{Arguments}:
@multitable @columnfractions .15 .70
@item @var{cptr}  @tab scalar of the type @code{C_FUNPTR}. It is
		       @code{INTENT(IN)}.
@item @var{fptr}  @tab procedure pointer interoperable with @var{cptr}. It is
		       @code{INTENT(OUT)}.
@end multitable

@item @emph{Example}:
@smallexample
program main
  use iso_c_binding
  implicit none
  abstract interface
    function func(a)
      import :: c_float
      real(c_float), intent(in) :: a
      real(c_float) :: func
    end function
  end interface
  interface
     function getIterFunc() bind(c,name="getIterFunc")
       import :: c_funptr
       type(c_funptr) :: getIterFunc
     end function
  end interface
  type(c_funptr) :: cfunptr
  procedure(func), pointer :: myFunc
  cfunptr = getIterFunc()
  call c_f_procpointer(cfunptr, myFunc)
end program main
@end smallexample

@item @emph{See also}:
@ref{C_LOC}, @ref{C_F_POINTER}
@end table


@node C_F_POINTER
@section @code{C_F_POINTER} --- Convert C into Fortran pointer
@fnindex C_F_POINTER
@cindex pointer, convert C to Fortran

@table @asis
@item @emph{Description}:
@code{C_F_POINTER(cptr, fptr[, shape])} Assign the target the C pointer
@var{cptr} to the Fortran pointer @var{fptr} and specify its
shape.

@item @emph{Standard}:
F2003 and later

@item @emph{Class}:
Subroutine

@item @emph{Syntax}:
@code{CALL C_F_POINTER(cptr, fptr[, shape])}

@item @emph{Arguments}:
@multitable @columnfractions .15 .70
@item @var{cptr}  @tab scalar of the type @code{C_PTR}. It is
		       @code{INTENT(IN)}.
@item @var{fptr}  @tab pointer interoperable with @var{cptr}. It is
		       @code{INTENT(OUT)}.
@item @var{shape} @tab (Optional) Rank-one array of type @code{INTEGER}
                       with @code{INTENT(IN)}. It shall be present
		       if and only if @var{fptr} is an array. The size
		       must be equal to the rank of @var{fptr}.
@end multitable

@item @emph{Example}:
@smallexample
program main
  use iso_c_binding
  implicit none
  interface
    subroutine my_routine(p) bind(c,name='myC_func')
      import :: c_ptr
      type(c_ptr), intent(out) :: p
    end subroutine
  end interface
  type(c_ptr) :: cptr
  real,pointer :: a(:)
  call my_routine(cptr)
  call c_f_pointer(cptr, a, [12])
end program main
@end smallexample

@item @emph{See also}:
@ref{C_LOC}, @ref{C_F_PROCPOINTER}
@end table


@node C_LOC
@section @code{C_LOC} --- Obtain the C address of an object
@fnindex C_LOC
@cindex procedure pointer, convert C to Fortran

@table @asis
@item @emph{Description}:
@code{C_LOC(x)} determines the C address of the argument.

@item @emph{Standard}:
F2003 and later

@item @emph{Class}:
Inquiry function

@item @emph{Syntax}:
@code{RESULT = C_LOC(x)}

@item @emph{Arguments}:
@multitable @columnfractions .15 .70
@item @var{x} @tab Associated scalar pointer or interoperable scalar
		   or allocated allocatable variable with @code{TARGET}
		   attribute.
@end multitable

@item @emph{Return value}:
The return value is of type @code{C_PTR} and contains the C address
of the argument.

@item @emph{Example}:
@smallexample
subroutine association_test(a,b)
  use iso_c_binding, only: c_associated, c_loc, c_ptr
  implicit none
  real, pointer :: a
  type(c_ptr) :: b
  if(c_associated(b, c_loc(a))) &
     stop 'b and a do not point to same target'
end subroutine association_test
@end smallexample

@item @emph{See also}:
@ref{C_ASSOCIATED}, @ref{C_FUNLOC}, @ref{C_F_POINTER}, @ref{C_F_PROCPOINTER}
@end table


@node CEILING
@section @code{CEILING} --- Integer ceiling function
@fnindex CEILING
@cindex ceiling
@cindex rounding, ceiling

@table @asis
@item @emph{Description}:
@code{CEILING(X)} returns the least integer greater than or equal to @var{X}.

@item @emph{Standard}:
F95 and later

@item @emph{Class}:
Elemental function

@item @emph{Syntax}:
@code{RESULT = CEILING(X [, KIND])}

@item @emph{Arguments}:
@multitable @columnfractions .15 .70
@item @var{X} @tab The type shall be @code{REAL(*)}.
@item @var{KIND} @tab (Optional) An @code{INTEGER(*)} initialization
                      expression indicating the kind parameter of
		      the result.
@end multitable

@item @emph{Return value}:
The return value is of type @code{INTEGER(KIND)}

@item @emph{Example}:
@smallexample
program test_ceiling
    real :: x = 63.29
    real :: y = -63.59
    print *, ceiling(x) ! returns 64
    print *, ceiling(y) ! returns -63
end program test_