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C Library Functions  - atomic_fetch_xor (3)

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NAME

ATOMIC_FETCH_XOR(3) - [ATOMIC:BIT MANIPULATION] Atomically fetch and perform a bitwise XOR operation

SYNOPSIS

call atomic_fetch_xor (atom, value, old [,stat] )

         subroutine atomic_fetch_xor (atom, value, old, stat)

CHARACTERISTICS

o	ATOM: A scalar coarray or coindexed variable of integer type with kind ATOMIC_INT_KIND.
o	VALUE: A scalar of the same type as ATOM.
o	OLD: A scalar of the same type and kind as ATOM.
o	STAT (optional): A scalar default-kind integer.

DESCRIPTION

ATOMIC_FETCH_XOR(ATOM, VALUE, OLD, STAT) atomically stores the value of ATOM in OLD and performs a bitwise XOR operation between ATOM and VALUE, storing the result in ATOM.

When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

The result is the bitwise XOR (e.g., 1100 XOR 1010 = 0110).

It is useful for toggling bits atomically.

OPTIONS

o	ATOM : Scalar coarray or coindexed variable of integer type with atomic_int_kind kind.
o	VALUE : Scalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
o	OLD : Scalar of the same type and kind as ATOM.
o	STAT : (optional) Scalar default-kind integer variable.

EXAMPLES

Sample program:

    program demo_atomic_fetch_xor

      use iso_fortran_env
      implicit none
      integer(atomic_int_kind) :: flags[*], old
      integer :: stat, me

      if (this_image() == 1) flags = int(b’1100’, atomic_int_kind)
      sync all

      me = this_image()
      call atomic_fetch_xor(flags[1], int(b’1010’, atomic_int_kind), old, stat)

      if (stat /= 0) print *, "Image", me, ": Failed with STAT =", stat
      print *, "Image", me, ": Old =", old
      sync all

      if (this_image() == 1) print *, "Final flags:", flags
    end program demo_atomic_fetch_xor

Expected Output (4 images, order varies)

        > Image 1: Old = 12
        > Image 2: Old = 6
        > Image 3: Old = 6
        > Image 4: Old = 6
        > Final flags: 6

STANDARD

TS 18508

SEE ALSO

ATOMIC_DEFINE(3), ATOMIC_XOR(3), ISO_FORTRAN_ENV(3),

ATOMIC_FETCH_ADD(3), ATOMIC_FETCH_AND(3),

ATOMIC_FETCH_OR(3)

See ISO_FORTRAN_ENV for constants like ATOMIC_INT_KIND, STAT_STOPPED_IMAGE, and STAT_FAILED_IMAGE.

Fortran intrinsic descriptions

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Nemo Release 3.1

atomic_fetch_xor (3)

June 29, 2025

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