(*)Write full checksums to restarts

  Change the types returned from the 5 rotated_field_chksum from integer to
integer(kind=int64), so that the full 64-byte checksums are returned.  Without
this change, the checksums that are written to MOM6 restart files or interpreted
from them are truncated to the latter half of their length.  This changes the
checksums that are written to the restart files, but both before and after this
change the values that are written are the same as those that are generated
after reading the restart with the same version of the code.  The code can run
across this change by setting RESTART_CHECKSUMS_REQUIRED = False for the run
segment where the transition occurs.  The solutions themselves are bitwise
identical.

src/framework/MOM_checksums.F90

@@ -5,14 +5,14 @@ module MOM_checksums
 
 use MOM_array_transform, only : rotate_array, rotate_array_pair, rotate_vector
 use MOM_array_transform, only : allocate_rotated_array
-use MOM_coms, only : PE_here, root_PE, num_PEs, sum_across_PEs
-use MOM_coms, only : min_across_PEs, max_across_PEs
-use MOM_coms, only : reproducing_sum, field_chksum
-use MOM_error_handler, only : MOM_error, FATAL, is_root_pe
-use MOM_file_parser, only : log_version, param_file_type
-use MOM_hor_index, only : hor_index_type, rotate_hor_index
+use MOM_coms,            only : PE_here, root_PE, num_PEs, sum_across_PEs
+use MOM_coms,            only : min_across_PEs, max_across_PEs
+use MOM_coms,            only : reproducing_sum, field_chksum
+use MOM_error_handler,   only : MOM_error, FATAL, is_root_pe
+use MOM_file_parser,     only : log_version, param_file_type
+use MOM_hor_index,       only : hor_index_type, rotate_hor_index
 
-use iso_fortran_env, only: error_unit
+use iso_fortran_env,     only : error_unit, int32, int64
 
 implicit none ; private
 
@@ -2092,7 +2092,7 @@ function rotated_field_chksum_real_0d(field, pelist, mask_val, turns) &
   integer, optional, intent(in) :: pelist(:)  !< PE list of ranks to checksum
   real,    optional, intent(in) :: mask_val   !< FMS mask value
   integer, optional, intent(in) :: turns      !< Number of quarter turns
-  integer :: chksum                           !< checksum of scalar
+  integer(kind=int64) :: chksum               !< checksum of scalar
 
   if (present(turns)) call MOM_error(FATAL, "Rotation not supported for 0d fields.")
 
@@ -2107,7 +2107,7 @@ function rotated_field_chksum_real_1d(field, pelist, mask_val, turns) &
   integer,  optional, intent(in) :: pelist(:) !< PE list of ranks to checksum
   real,     optional, intent(in) :: mask_val  !< FMS mask value
   integer,  optional, intent(in) :: turns     !< Number of quarter turns
-  integer :: chksum                           !< checksum of array
+  integer(kind=int64) :: chksum               !< checksum of array
 
   if (present(turns)) call MOM_error(FATAL, "Rotation not supported for 1d fields.")
 
@@ -2122,7 +2122,7 @@ function rotated_field_chksum_real_2d(field, pelist, mask_val, turns) &
   integer,        optional, intent(in) :: pelist(:) !< PE list of ranks to checksum
   real,           optional, intent(in) :: mask_val  !< FMS mask value
   integer,        optional, intent(in) :: turns     !< Number of quarter turns
-  integer :: chksum                                 !< checksum of array
+  integer(kind=int64) :: chksum                     !< checksum of array
 
   ! Local variables
   real, allocatable :: field_rot(:,:)  ! A rotated version of field, with the same units
@@ -2149,7 +2149,7 @@ function rotated_field_chksum_real_3d(field, pelist, mask_val, turns) &
   integer,        optional, intent(in) :: pelist(:) !< PE list of ranks to checksum
   real,           optional, intent(in) :: mask_val  !< FMS mask value
   integer,        optional, intent(in) :: turns     !< Number of quarter turns
-  integer :: chksum                                 !< checksum of array
+  integer(kind=int64) :: chksum                     !< checksum of array
 
   ! Local variables
   real, allocatable :: field_rot(:,:,:)  ! A rotated version of field, with the same units
@@ -2176,7 +2176,7 @@ function rotated_field_chksum_real_4d(field, pelist, mask_val, turns) &
   integer,        optional, intent(in) :: pelist(:) !< PE list of ranks to checksum
   real,           optional, intent(in) :: mask_val  !< FMS mask value
   integer,        optional, intent(in) :: turns     !< Number of quarter turns
-  integer :: chksum                                 !< checksum of array
+  integer(kind=int64) :: chksum                     !< checksum of array
 
   ! Local variables
   real, allocatable :: field_rot(:,:,:,:)  ! A rotated version of field, with the same units