Support of int32 index array in sort_index

doc/specs/stdlib_sorting.md

@@ -24,17 +24,18 @@ module's `string_type` type.
 
 ## Overview of the module
 
-The module `stdlib_sorting` defines several public entities, one
-default integer parameter, `int_index`, and four overloaded
+The module `stdlib_sorting` defines several public entities, two
+default integer parameters, `int_index` and `int_index_low`, and four overloaded
 subroutines: `ORD_SORT`, `SORT`, `RADIX_SORT` and `SORT_INDEX`. The
 overloaded subroutines also each have several specific names for
 versions corresponding to different types of array arguments.
 
-### The `int_index` parameter
+### The parameters `int_index` and `int_index_low`
 
-The `int_index` parameter is used to specify the kind of integer used
-in indexing the various arrays. Currently the module sets `int_index`
-to the value of `int64` from the `stdlib_kinds` module.
+The parameters `int_index` and `int_index_low` are used to specify the kind of integer used
+in indexing the various arrays. Currently the module sets `int_index` and
+`int_index_low`
+to the value of `int64` and `int32` from the `stdlib_kinds` module, respectively.
 
 ### The module subroutines
 
@@ -414,7 +415,7 @@ It is an `intent(inout)` argument. On input it
 will be an array whose sorting indices are to be determined. On return
 it will be the sorted array.
 
-`index`: shall be a rank one integer array of kind `int_index` and of
+`index`: shall be a rank one integer array of kind `int_index` or `int_index_low` and of
 the size of `array`. It is an `intent(out)` argument. On return it
 shall have values that are the indices needed to sort the original
 array in the desired direction.
@@ -426,8 +427,8 @@ memory for internal record keeping. If associated with an array in
 static storage, its use can significantly reduce the stack memory
 requirements for the code. Its contents on return are undefined.
 
-`iwork` (optional): shall be a rank one integer array of kind
-`int_index`, and shall have at least `size(array)/2` elements. It
+`iwork` (optional): shall be a rank one integer array of the same kind
+of the array `index`, and shall have at least `size(array)/2` elements. It
 is an `intent(out)` argument.  It is intended to be used as "scratch"
 memory for internal record keeping. If associated with an array in
 static storage, its use can significantly reduce the stack memory
@@ -457,6 +458,12 @@ different on return
 
 ##### Examples
 
+Sorting a rank one array with `sort_index`:
+
+```Fortran
+{!example/sorting/example_sort_index.f90!}
+```
+
 Sorting a related rank one array:
 
 ```Fortran
@@ -504,7 +511,7 @@ Sorting an array of a derived type based on the data in one component
 
 ```fortran
     subroutine sort_a_data( a_data, a, work, index, iwork )
-        ! Sort `a_data` in terms or its component `a`
+        ! Sort `a_data` in terms of its component `a`
         type(a_type), intent(inout)      :: a_data(:)
         integer(int32), intent(inout)    :: a(:)
         integer(int32), intent(out)    :: work(:)

example/sorting/CMakeLists.txt

@@ -1,4 +1,5 @@
 ADD_EXAMPLE(ord_sort)
 ADD_EXAMPLE(sort)
+ADD_EXAMPLE(sort_index)
 ADD_EXAMPLE(radix_sort)
-ADD_EXAMPLE(sort_bitset)
+ADD_EXAMPLE(sort_bitset)

example/sorting/example_sort_index.f90

@@ -0,0 +1,15 @@
+program example_sort_index
+  use stdlib_sorting, only: sort_index
+  implicit none
+  integer, allocatable :: array(:)
+  integer, allocatable :: index(:)
+
+  array = [5, 4, 3, 1, 10, 4, 9]
+  allocate(index, mold=array)
+
+  call sort_index(array, index)
+
+  print *, array   !print [1, 3, 4, 4, 5, 9, 10]
+  print *, index   !print [4, 3, 2, 6, 1, 7, 5]
+
+end program example_sort_index

src/stdlib_sorting.fypp

@@ -6,6 +6,8 @@
 #:set CHAR_TYPES_ALT_NAME = list(zip(["character(len=*)"], ["character(len=len(array))"], ["char"]))
 #:set BITSET_TYPES_ALT_NAME = list(zip(BITSET_TYPES, BITSET_TYPES, BITSET_KINDS))
 
+#:set INT_INDEX_TYPES_ALT_NAME = list(zip(["int_index", "int_index_low"], ["integer(int_index)", "integer(int_index_low)"], ["default", "low"]))
+
 #! For better code reuse in fypp, make lists that contain the input types,
 #! with each having output types and a separate name prefix for subroutines
 #! This approach allows us to have the same code for all input types.
@@ -138,6 +140,8 @@ module stdlib_sorting
     private
 
     integer, parameter, public :: int_index = int64 !! Integer kind for indexing
+    integer, parameter, public :: int_index_low = int32 !! Integer kind for indexing using less than `huge(1_int32)` values
+
 
 ! Constants for use by tim_sort
     integer, parameter :: &
@@ -147,14 +151,16 @@ module stdlib_sorting
         max_merge_stack = int( ceiling( log( 2._dp**64 ) / &
                                log(1.6180339887_dp) ) )
 
-    type run_type
+#:for ki, ti, namei in INT_INDEX_TYPES_ALT_NAME
+    type run_type_${namei}$
 !! Version: experimental
 !!
 !! Used to pass state around in a stack among helper functions for the
 !! `ORD_SORT` and `SORT_INDEX` algorithms
-        integer(int_index) :: base = 0
-        integer(int_index) :: len = 0
-    end type run_type
+        ${ti}$ :: base = 0
+        ${ti}$ :: len = 0
+    end type run_type_${namei}$
+#:endfor
 
     public ord_sort
 !! Version: experimental
@@ -515,23 +521,25 @@ module stdlib_sorting
 !! non-decreasing sort, but if the optional argument `REVERSE` is present
 !! with a value of `.TRUE.` the indices correspond to a non-increasing sort.
 
-#:for t1, t2, name1 in IRSCB_TYPES_ALT_NAME
-        module subroutine ${name1}$_sort_index( array, index, work, iwork, &
+#:for ki, ti, namei in INT_INDEX_TYPES_ALT_NAME
+    #:for t1, t2, name1 in IRSCB_TYPES_ALT_NAME
+        module subroutine ${name1}$_sort_index_${namei}$( array, index, work, iwork, &
             reverse )
 !! Version: experimental
 !!
-!! `${name1}$_sort_index( array, index[, work, iwork, reverse] )` sorts
+!! `${name1}$_sort_index_${namei}$( array, index[, work, iwork, reverse] )` sorts
 !! an input `ARRAY` of type `${t1}$`
 !! using a hybrid sort based on the `"Rust" sort` algorithm found in `slice.rs`
 !! and returns the sorted `ARRAY` and an array `INDEX` of indices in the
 !! order that would sort the input `ARRAY` in the desired direction.
             ${t1}$, intent(inout)                     :: array(0:)
-            integer(int_index), intent(out)           :: index(0:)
+            ${ti}$, intent(out)                      :: index(0:)
             ${t2}$, intent(out), optional             :: work(0:)
-            integer(int_index), intent(out), optional :: iwork(0:)
+            ${ti}$, intent(out), optional            :: iwork(0:)
             logical, intent(in), optional             :: reverse
-        end subroutine ${name1}$_sort_index
+        end subroutine ${name1}$_sort_index_${namei}$
 
+    #:endfor
 #:endfor
 
     end interface sort_index

src/stdlib_sorting_ord_sort.fypp

@@ -186,7 +186,7 @@ contains
 ! 1. len(-3) > len(-2) + len(-1)
 ! 2. len(-2) > len(-1)
             integer(int_index) :: r
-            type(run_type), intent(in), target :: runs(0:)
+            type(run_type_default), intent(in), target :: runs(0:)
 
             integer(int_index) :: n
             logical :: test
@@ -277,7 +277,7 @@ contains
 
             integer(int_index) :: array_size, finish, min_run, r, r_count, &
                 start
-            type(run_type) :: runs(0:max_merge_stack-1), left, right
+            type(run_type_default) :: runs(0:max_merge_stack-1), left, right
 
             array_size = size(array, kind=int_index)
 
@@ -326,7 +326,7 @@ contains
                 end do Insert
                 if ( start == 0 .and. finish == array_size - 1 ) return
 
-                runs(r_count) = run_type( base = start, &
+                runs(r_count) = run_type_default( base = start, &
                                           len = finish - start + 1 )
                 finish = start-1
                 r_count = r_count + 1
@@ -342,7 +342,7 @@ contains
                                        right % base + right % len - 1 ), &
                                 left % len, buf )
 
-                    runs(r) = run_type( base = left % base, &
+                    runs(r) = run_type_default( base = left % base, &
                                         len = left % len + right % len )
                     if ( r == r_count - 3 ) runs(r+1) = runs(r+2)
                     r_count = r_count - 1