From fe02d4b3af099f155296e0a1eee136ed2f229388 Mon Sep 17 00:00:00 2001
From: jalvesz <jose.alves@transvalor.com>
Date: Tue, 3 Sep 2024 22:04:46 +0200
Subject: [PATCH 01/15] elemental swap

---
 doc/specs/stdlib_math.md           | 32 ++++++++++++++++++++++
 example/math/CMakeLists.txt        |  1 +
 example/math/example_math_swap.f90 | 33 +++++++++++++++++++++++
 src/stdlib_math.fypp               | 43 +++++++++++++++++++++++++++++-
 4 files changed, 108 insertions(+), 1 deletion(-)
 create mode 100644 example/math/example_math_swap.f90

diff --git a/doc/specs/stdlib_math.md b/doc/specs/stdlib_math.md
index f8cf15227..71806a9dc 100644
--- a/doc/specs/stdlib_math.md
+++ b/doc/specs/stdlib_math.md
@@ -61,6 +61,38 @@ Here inputs are of type `real` and kind `sp`
 {!example/math/example_clip_real.f90!}
 ```
 
+<!-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -->
+### `swap` function
+
+#### Description
+
+Swaps the values in `lhs` and `rhs`.
+
+#### Syntax
+
+`call` [[stdlib_math(module):swap(interface)]] ` (lhs, rhs)`
+
+#### Status
+
+Experimental
+
+#### Class
+
+Elemental function.
+
+#### Argument(s)
+
+`lhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character` type. This argument is `intent(inout)`.
+`rhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character` type. This argument is `intent(inout)`.
+
+Note: All arguments must have same `type` and same `kind`.
+
+#### Example
+
+```fortran
+{!example/math/example_math_swap.f90!}
+```
+
 ### `gcd` function
 
 #### Description
diff --git a/example/math/CMakeLists.txt b/example/math/CMakeLists.txt
index 0a1411bb9..8b834f348 100644
--- a/example/math/CMakeLists.txt
+++ b/example/math/CMakeLists.txt
@@ -15,4 +15,5 @@ ADD_EXAMPLE(math_argpi)
 ADD_EXAMPLE(math_deg2rad)
 ADD_EXAMPLE(math_rad2deg)
 ADD_EXAMPLE(math_is_close)
+ADD_EXAMPLE(math_swap)
 ADD_EXAMPLE(meshgrid)
diff --git a/example/math/example_math_swap.f90 b/example/math/example_math_swap.f90
new file mode 100644
index 000000000..444e3c713
--- /dev/null
+++ b/example/math/example_math_swap.f90
@@ -0,0 +1,33 @@
+program example_math_swap
+    use stdlib_math, only: swap
+    implicit none
+    
+    block
+        integer :: x, y
+        x = 9
+        y = 18
+        call swap(x,y)
+    end block
+
+    block
+        real :: x, y
+        x = 4.0
+        y = 8.0
+        call swap(x,y)
+    end block
+
+    block
+        real :: x(3), y(3)
+        x = [1.0,2.0,3.0]
+        y = [4.0,5.0,6.0]
+        call swap(x,y)
+    end block
+
+    block
+        character(5) :: x, y
+        x = 'abcde'
+        y = 'fghij'
+        call swap(x,y)
+    end block
+
+end program example_math_swap  
\ No newline at end of file
diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index 92a946cd9..d94b1ecfd 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -8,7 +8,7 @@ module stdlib_math
 
     implicit none
     private
-    public :: clip, gcd, linspace, logspace
+    public :: clip, swap, gcd, linspace, logspace
     public :: EULERS_NUMBER_SP, EULERS_NUMBER_DP
 #:if WITH_QP
     public :: EULERS_NUMBER_QP
@@ -42,6 +42,17 @@ module stdlib_math
     #:endfor
     end interface clip
 
+    interface swap
+      #:for k1, t1 in INT_KINDS_TYPES + REAL_KINDS_TYPES
+      module procedure :: swap_${k1}$
+      #:endfor
+      #:for k1, t1 in CMPLX_KINDS_TYPES
+      module procedure :: swap_c${k1}$
+      #:endfor
+      module procedure :: swap_bool
+      module procedure :: swap_str
+    end interface
+
     !> Returns the greatest common divisor of two integers
     !> ([Specification](../page/specs/stdlib_math.html#gcd))
     !>
@@ -509,5 +520,35 @@ contains
     end function gcd_${k1}$
 
     #:endfor
+
+    #:for k1, t1 in INT_KINDS_TYPES + REAL_KINDS_TYPES
+    elemental subroutine swap_${k1}$(lhs, rhs)
+        ${t1}$, intent(inout) :: lhs, rhs
+        ${t1}$ :: temp
+        temp = lhs; lhs = rhs; rhs = temp
+    end subroutine
+
+    #:endfor
+
+    #:for k1, t1 in CMPLX_KINDS_TYPES
+    elemental subroutine swap_c${k1}$(lhs, rhs)
+        ${t1}$, intent(inout) :: lhs, rhs
+        ${t1}$ :: temp
+        temp = lhs; lhs = rhs; rhs = temp
+    end subroutine
+
+    #:endfor
+
+    elemental subroutine swap_bool(lhs, rhs)
+        logical, intent(inout) :: lhs, rhs
+        logical :: temp
+        temp = lhs; lhs = rhs; rhs = temp
+    end subroutine
+
+    elemental subroutine swap_str(lhs, rhs)
+        character(1), intent(inout) :: lhs, rhs
+        character(1) :: temp
+        temp = lhs; lhs = rhs; rhs = temp
+    end subroutine
     
 end module stdlib_math

From 0fa4450f9ab288baa424da8729788f37cb9cf6ea Mon Sep 17 00:00:00 2001
From: jalvesz <jose.alves@transvalor.com>
Date: Tue, 3 Sep 2024 23:51:08 +0200
Subject: [PATCH 02/15] add tests, change string swap

---
 src/stdlib_math.fypp            |  8 ++---
 test/math/test_stdlib_math.fypp | 60 ++++++++++++++++++++++++++++++++-
 2 files changed, 63 insertions(+), 5 deletions(-)

diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index d94b1ecfd..1e41a6781 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -545,10 +545,10 @@ contains
         temp = lhs; lhs = rhs; rhs = temp
     end subroutine
 
-    elemental subroutine swap_str(lhs, rhs)
-        character(1), intent(inout) :: lhs, rhs
-        character(1) :: temp
-        temp = lhs; lhs = rhs; rhs = temp
+    elemental subroutine swap_str(lhs,rhs)
+        character(*), intent(inout) :: lhs, rhs
+        character(len=max(len(lhs),len(rhs))) :: temp
+        temp = lhs ; lhs = rhs ; rhs = temp
     end subroutine
     
 end module stdlib_math
diff --git a/test/math/test_stdlib_math.fypp b/test/math/test_stdlib_math.fypp
index 1f64622e4..f38f2d7bb 100644
--- a/test/math/test_stdlib_math.fypp
+++ b/test/math/test_stdlib_math.fypp
@@ -4,7 +4,7 @@
 
 module test_stdlib_math
     use testdrive, only : new_unittest, unittest_type, error_type, check, skip_test
-    use stdlib_math, only: clip, arg, argd, argpi, arange, is_close, all_close, diff, &
+    use stdlib_math, only: clip, swap, arg, argd, argpi, arange, is_close, all_close, diff, &
                            arange, deg2rad, rad2deg
     use stdlib_kinds, only: int8, int16, int32, int64, sp, dp, xdp, qp
     implicit none
@@ -38,6 +38,15 @@ contains
             new_unittest("clip-real-quad", test_clip_rqp), &
             new_unittest("clip-real-quad-bounds", test_clip_rqp_bounds) &
             
+            !> Tests swap
+            #:for k1, t1 in INT_KINDS_TYPES + REAL_KINDS_TYPES
+            , new_unittest("swap_${k1}$", test_swap_${k1}$) &
+            #:endfor
+            #:for k1, t1 in CMPLX_KINDS_TYPES
+            , new_unittest("swap_c${k1}$", test_swap_c${k1}$) &
+            #:endfor
+            , new_unittest("swap_str", test_swap_str) &
+
             !> Tests for arg/argd/argpi
             #:for k1 in CMPLX_KINDS
             , new_unittest("arg-cmplx-${k1}$", test_arg_${k1}$) &
@@ -246,6 +255,55 @@ contains
 
     end subroutine test_clip_rqp_bounds
 
+    #:for k1, t1 in INT_KINDS_TYPES + REAL_KINDS_TYPES
+    subroutine test_swap_${k1}$(error)
+        type(error_type), allocatable, intent(out) :: error
+        ${t1}$ :: x(3), y(3)
+        
+        x = [${t1}$ :: 1, 2, 3]
+        y = [${t1}$ :: 4, 5, 6]
+
+        call swap(x,y)
+        
+        call check(error, all( x == [${t1}$ :: 4, 5, 6] ) )
+        if (allocated(error)) return
+        call check(error, all( y == [${t1}$ :: 1, 2, 3] ) )
+        if (allocated(error)) return
+    end subroutine test_swap_${k1}$
+    #:endfor
+
+    #:for k1, t1 in CMPLX_KINDS_TYPES
+    subroutine test_swap_c${k1}$(error)
+        type(error_type), allocatable, intent(out) :: error
+        ${t1}$ :: x(3), y(3)
+        
+        x = cmplx( [1, 2, 3] , [4, 5, 6] )
+        y = cmplx( [4, 5, 6] , [1, 2, 3] )
+
+        call swap(x,y)
+        
+        call check(error, all( x == cmplx( [4, 5, 6] , [1, 2, 3] ) ) )
+        if (allocated(error)) return
+        call check(error, all( y == cmplx( [1, 2, 3] , [4, 5, 6] ) ) )
+        if (allocated(error)) return
+    end subroutine test_swap_c${k1}$
+    #:endfor
+
+    subroutine test_swap_str(error)
+        type(error_type), allocatable, intent(out) :: error
+        character(5) :: x(2), y(2)
+        
+        x = ['abcde','fghij'] 
+        y = ['fghij','abcde']
+
+        call swap(x,y)
+        
+        call check(error, all( x == ['fghij','abcde'] ) )
+        if (allocated(error)) return
+        call check(error, all( y == ['abcde','fghij']  ) )
+        if (allocated(error)) return
+    end subroutine test_swap_str
+
     #:for k1 in CMPLX_KINDS
     subroutine test_arg_${k1}$(error)
         type(error_type), allocatable, intent(out) :: error

From 0daa4d8903ac5df59af488ea7f3a3d56046bbe9d Mon Sep 17 00:00:00 2001
From: jalvesz <jose.alves@transvalor.com>
Date: Sun, 8 Sep 2024 21:35:13 +0200
Subject: [PATCH 03/15] add self swap tests

---
 test/math/test_stdlib_math.fypp | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/test/math/test_stdlib_math.fypp b/test/math/test_stdlib_math.fypp
index f38f2d7bb..8accb8bb4 100644
--- a/test/math/test_stdlib_math.fypp
+++ b/test/math/test_stdlib_math.fypp
@@ -269,6 +269,12 @@ contains
         if (allocated(error)) return
         call check(error, all( y == [${t1}$ :: 1, 2, 3] ) )
         if (allocated(error)) return
+
+        ! check self swap
+        call swap(x,x)
+
+        call check(error, all( x == [${t1}$ :: 4, 5, 6] ) )
+        if (allocated(error)) return
     end subroutine test_swap_${k1}$
     #:endfor
 
@@ -286,6 +292,12 @@ contains
         if (allocated(error)) return
         call check(error, all( y == cmplx( [1, 2, 3] , [4, 5, 6] ) ) )
         if (allocated(error)) return
+
+        ! check self swap
+        call swap(x,x)
+        
+        call check(error, all( x == cmplx( [4, 5, 6] , [1, 2, 3] ) ) )
+        if (allocated(error)) return
     end subroutine test_swap_c${k1}$
     #:endfor
 
@@ -302,6 +314,12 @@ contains
         if (allocated(error)) return
         call check(error, all( y == ['abcde','fghij']  ) )
         if (allocated(error)) return
+
+        ! check self swap
+        call swap(x,x)
+        
+        call check(error, all( x == ['fghij','abcde'] ) )
+        if (allocated(error)) return
     end subroutine test_swap_str
 
     #:for k1 in CMPLX_KINDS

From 5a75fa3fa369a7549bf6ec846feec38363e02176 Mon Sep 17 00:00:00 2001
From: jalvesz <jose.alves@transvalor.com>
Date: Mon, 9 Sep 2024 18:57:08 +0200
Subject: [PATCH 04/15] add swap for stdlib string_type

---
 doc/specs/stdlib_math.md           |  4 ++--
 example/math/example_math_swap.f90 |  8 ++++++++
 src/stdlib_math.fypp               |  8 ++++++++
 test/math/test_stdlib_math.fypp    | 23 +++++++++++++++++++++++
 4 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/doc/specs/stdlib_math.md b/doc/specs/stdlib_math.md
index 71806a9dc..1889f1591 100644
--- a/doc/specs/stdlib_math.md
+++ b/doc/specs/stdlib_math.md
@@ -82,8 +82,8 @@ Elemental function.
 
 #### Argument(s)
 
-`lhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character` type. This argument is `intent(inout)`.
-`rhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character` type. This argument is `intent(inout)`.
+`lhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character`, `string_type` type. This argument is `intent(inout)`.
+`rhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character`, `string_type` type. This argument is `intent(inout)`.
 
 Note: All arguments must have same `type` and same `kind`.
 
diff --git a/example/math/example_math_swap.f90 b/example/math/example_math_swap.f90
index 444e3c713..cba9b37f6 100644
--- a/example/math/example_math_swap.f90
+++ b/example/math/example_math_swap.f90
@@ -30,4 +30,12 @@ program example_math_swap
         call swap(x,y)
     end block
 
+    block
+        use stdlib_string_type
+        type(string_type) :: x, y
+        x = 'abcde'
+        y = 'fghij'
+        call swap(x,y)
+    end block
+
 end program example_math_swap  
\ No newline at end of file
diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index 1e41a6781..ece280554 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -51,6 +51,7 @@ module stdlib_math
       #:endfor
       module procedure :: swap_bool
       module procedure :: swap_str
+      module procedure :: swap_stt
     end interface
 
     !> Returns the greatest common divisor of two integers
@@ -550,5 +551,12 @@ contains
         character(len=max(len(lhs),len(rhs))) :: temp
         temp = lhs ; lhs = rhs ; rhs = temp
     end subroutine
+
+    elemental subroutine swap_stt(lhs,rhs)
+        use stdlib_string_type
+        type(string_type), intent(inout) :: lhs, rhs
+        type(string_type) :: temp
+        temp = lhs ; lhs = rhs ; rhs = temp
+    end subroutine
     
 end module stdlib_math
diff --git a/test/math/test_stdlib_math.fypp b/test/math/test_stdlib_math.fypp
index 8accb8bb4..c477ebdbc 100644
--- a/test/math/test_stdlib_math.fypp
+++ b/test/math/test_stdlib_math.fypp
@@ -46,6 +46,7 @@ contains
             , new_unittest("swap_c${k1}$", test_swap_c${k1}$) &
             #:endfor
             , new_unittest("swap_str", test_swap_str) &
+            , new_unittest("swap_stt", test_swap_stt) &
 
             !> Tests for arg/argd/argpi
             #:for k1 in CMPLX_KINDS
@@ -322,6 +323,28 @@ contains
         if (allocated(error)) return
     end subroutine test_swap_str
 
+    subroutine test_swap_stt(error)
+        use stdlib_string_type
+        type(error_type), allocatable, intent(out) :: error
+        type(string_type) :: x(2), y(2)
+        
+        x = ['abcde','fghij'] 
+        y = ['fghij','abcde']
+
+        call swap(x,y)
+        
+        call check(error, all( x == ['fghij','abcde'] ) )
+        if (allocated(error)) return
+        call check(error, all( y == ['abcde','fghij']  ) )
+        if (allocated(error)) return
+
+        ! check self swap
+        call swap(x,x)
+        
+        call check(error, all( x == ['fghij','abcde'] ) )
+        if (allocated(error)) return
+    end subroutine test_swap_stt
+
     #:for k1 in CMPLX_KINDS
     subroutine test_arg_${k1}$(error)
         type(error_type), allocatable, intent(out) :: error

From e9b9c106e66e0f506959777c2caceca3a5d54a71 Mon Sep 17 00:00:00 2001
From: jalvesz <102541118+jalvesz@users.noreply.github.com>
Date: Tue, 10 Sep 2024 09:41:38 +0200
Subject: [PATCH 05/15] Update doc/specs/stdlib_math.md

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>
---
 doc/specs/stdlib_math.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/specs/stdlib_math.md b/doc/specs/stdlib_math.md
index 1889f1591..96399daeb 100644
--- a/doc/specs/stdlib_math.md
+++ b/doc/specs/stdlib_math.md
@@ -62,7 +62,7 @@ Here inputs are of type `real` and kind `sp`
 ```
 
 <!-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -->
-### `swap` function
+### `swap` subroutine
 
 #### Description
 

From e35beca192e3b70b71d37e2d591f59b7c0081753 Mon Sep 17 00:00:00 2001
From: jalvesz <102541118+jalvesz@users.noreply.github.com>
Date: Tue, 10 Sep 2024 09:41:50 +0200
Subject: [PATCH 06/15] Update doc/specs/stdlib_math.md

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>
---
 doc/specs/stdlib_math.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/specs/stdlib_math.md b/doc/specs/stdlib_math.md
index 96399daeb..3e510e26a 100644
--- a/doc/specs/stdlib_math.md
+++ b/doc/specs/stdlib_math.md
@@ -78,7 +78,7 @@ Experimental
 
 #### Class
 
-Elemental function.
+Elemental subroutine.
 
 #### Argument(s)
 

From 6a30b2ff974aaa9a0a27aa730e0ece321c8b13ac Mon Sep 17 00:00:00 2001
From: jalvesz <jose.alves@transvalor.com>
Date: Tue, 10 Sep 2024 21:33:08 +0200
Subject: [PATCH 07/15] autodoc

---
 src/stdlib_math.fypp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index ece280554..c302f5621 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -42,6 +42,10 @@ module stdlib_math
     #:endfor
     end interface clip
 
+    !> Swap the values of the lhs and rhs arguments
+    !> ([Specification](../page/specs/stdlib_math.html#swap))
+    !>
+    !> Version: experimental
     interface swap
       #:for k1, t1 in INT_KINDS_TYPES + REAL_KINDS_TYPES
       module procedure :: swap_${k1}$

From 1993d628402a8cb9fc90fca78da222f73fcfb393 Mon Sep 17 00:00:00 2001
From: jalvesz <jose.alves@transvalor.com>
Date: Wed, 11 Sep 2024 23:57:46 +0200
Subject: [PATCH 08/15] add bitset support

---
 doc/specs/stdlib_math.md           |  4 +--
 example/math/example_math_swap.f90 |  8 ++++++
 src/stdlib_math.fypp               | 14 +++++++--
 test/math/test_stdlib_math.fypp    | 46 ++++++++++++++++++++++++++++++
 4 files changed, 68 insertions(+), 4 deletions(-)

diff --git a/doc/specs/stdlib_math.md b/doc/specs/stdlib_math.md
index 3e510e26a..8fa32084b 100644
--- a/doc/specs/stdlib_math.md
+++ b/doc/specs/stdlib_math.md
@@ -82,8 +82,8 @@ Elemental subroutine.
 
 #### Argument(s)
 
-`lhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character`, `string_type` type. This argument is `intent(inout)`.
-`rhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character`, `string_type` type. This argument is `intent(inout)`.
+`lhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character`, `string_type`, `bitset` type. This argument is `intent(inout)`.
+`rhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character`, `string_type`, `bitset` type. This argument is `intent(inout)`.
 
 Note: All arguments must have same `type` and same `kind`.
 
diff --git a/example/math/example_math_swap.f90 b/example/math/example_math_swap.f90
index cba9b37f6..8a34853c8 100644
--- a/example/math/example_math_swap.f90
+++ b/example/math/example_math_swap.f90
@@ -38,4 +38,12 @@ program example_math_swap
         call swap(x,y)
     end block
 
+    block
+        use stdlib_bitsets
+        type(bitset_64) :: x, y
+        call x%from_string('0000')
+        call y%from_string('1111')
+        call swap(x,y)
+    end block
+
 end program example_math_swap  
\ No newline at end of file
diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index c302f5621..bc26365d3 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -1,7 +1,7 @@
 #:include "common.fypp"
 #:set IR_KINDS_TYPES = INT_KINDS_TYPES + REAL_KINDS_TYPES
 #:set RC_KINDS_TYPES = REAL_KINDS_TYPES + CMPLX_KINDS_TYPES
-
+#:set BITSET_KINDS_TYPES = list(zip(BITSET_KINDS, BITSET_TYPES))
 module stdlib_math
     use stdlib_kinds, only: int8, int16, int32, int64, sp, dp, xdp, qp
     use stdlib_optval, only: optval
@@ -47,7 +47,7 @@ module stdlib_math
     !>
     !> Version: experimental
     interface swap
-      #:for k1, t1 in INT_KINDS_TYPES + REAL_KINDS_TYPES
+      #:for k1, t1 in INT_KINDS_TYPES + REAL_KINDS_TYPES + BITSET_KINDS_TYPES
       module procedure :: swap_${k1}$
       #:endfor
       #:for k1, t1 in CMPLX_KINDS_TYPES
@@ -562,5 +562,15 @@ contains
         type(string_type) :: temp
         temp = lhs ; lhs = rhs ; rhs = temp
     end subroutine
+
+    #:for k1, t1 in BITSET_KINDS_TYPES
+    elemental subroutine swap_${k1}$(lhs,rhs)
+        use stdlib_bitsets
+        ${t1}$, intent(inout) :: lhs, rhs
+        ${t1}$ :: temp
+        temp = lhs ; lhs = rhs ; rhs = temp
+    end subroutine
+
+    #:endfor
     
 end module stdlib_math
diff --git a/test/math/test_stdlib_math.fypp b/test/math/test_stdlib_math.fypp
index c477ebdbc..834b2f1dd 100644
--- a/test/math/test_stdlib_math.fypp
+++ b/test/math/test_stdlib_math.fypp
@@ -345,6 +345,52 @@ contains
         if (allocated(error)) return
     end subroutine test_swap_stt
 
+    subroutine test_swap_bitset_64(error)
+        use stdlib_bitsets
+        type(error_type), allocatable, intent(out) :: error
+        type(bitset_64) :: x, y, u, v
+        
+        x = [.true.,.false.,.true.,.false.] 
+        u = x
+        y = [.false.,.true.,.false.,.true.]
+        v = y
+        call swap(x,y)
+        
+        call check(error, x == v )
+        if (allocated(error)) return
+        call check(error, y == u  )
+        if (allocated(error)) return
+
+        ! check self swap
+        call swap(x,x)
+        
+        call check(error, x == v )
+        if (allocated(error)) return
+    end subroutine test_swap_bitset_64
+
+    subroutine test_swap_bitset_large(error)
+        use stdlib_bitsets
+        type(error_type), allocatable, intent(out) :: error
+        type(bitset_large) :: x, y, u, v
+        
+        x = [.true.,.false.,.true.,.false.] 
+        u = x
+        y = [.false.,.true.,.false.,.true.]
+        v = y
+        call swap(x,y)
+        
+        call check(error, x == v )
+        if (allocated(error)) return
+        call check(error, y == u )
+        if (allocated(error)) return
+
+        ! check self swap
+        call swap(x,x)
+        
+        call check(error, x == v )
+        if (allocated(error)) return
+    end subroutine test_swap_bitset_large
+
     #:for k1 in CMPLX_KINDS
     subroutine test_arg_${k1}$(error)
         type(error_type), allocatable, intent(out) :: error

From 66175e7ae11cf1b06f57276cd2e42bf6187865f1 Mon Sep 17 00:00:00 2001
From: jalvesz <102541118+jalvesz@users.noreply.github.com>
Date: Sun, 15 Sep 2024 21:14:19 +0200
Subject: [PATCH 09/15] Update src/stdlib_math.fypp

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>
---
 src/stdlib_math.fypp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index bc26365d3..7959b541a 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -557,7 +557,7 @@ contains
     end subroutine
 
     elemental subroutine swap_stt(lhs,rhs)
-        use stdlib_string_type
+        use stdlib_string_type, only: string_type
         type(string_type), intent(inout) :: lhs, rhs
         type(string_type) :: temp
         temp = lhs ; lhs = rhs ; rhs = temp

From c2a0bada9bf42e0839318d9178369ec008b1f64a Mon Sep 17 00:00:00 2001
From: jalvesz <102541118+jalvesz@users.noreply.github.com>
Date: Sun, 15 Sep 2024 21:15:19 +0200
Subject: [PATCH 10/15] Update src/stdlib_math.fypp

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>
---
 src/stdlib_math.fypp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index 7959b541a..4a026785d 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -43,7 +43,7 @@ module stdlib_math
     end interface clip
 
     !> Swap the values of the lhs and rhs arguments
-    !> ([Specification](../page/specs/stdlib_math.html#swap))
+    !> ([Specification](../page/specs/stdlib_math.html#swap_subroutine))
     !>
     !> Version: experimental
     interface swap

From 7370020e002c4f75b050869bb316b1a6f26b1857 Mon Sep 17 00:00:00 2001
From: jalvesz <jose.alves@transvalor.com>
Date: Sun, 15 Sep 2024 21:39:05 +0200
Subject: [PATCH 11/15] move swap bitset within same fypp loop as for integers
 and reals

---
 src/stdlib_math.fypp | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index 4a026785d..49c63cd51 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -5,6 +5,7 @@
 module stdlib_math
     use stdlib_kinds, only: int8, int16, int32, int64, sp, dp, xdp, qp
     use stdlib_optval, only: optval
+    use stdlib_bitsets, only: bitset_64, bitset_large
 
     implicit none
     private
@@ -526,7 +527,7 @@ contains
 
     #:endfor
 
-    #:for k1, t1 in INT_KINDS_TYPES + REAL_KINDS_TYPES
+    #:for k1, t1 in INT_KINDS_TYPES + REAL_KINDS_TYPES + BITSET_KINDS_TYPES
     elemental subroutine swap_${k1}$(lhs, rhs)
         ${t1}$, intent(inout) :: lhs, rhs
         ${t1}$ :: temp
@@ -562,15 +563,5 @@ contains
         type(string_type) :: temp
         temp = lhs ; lhs = rhs ; rhs = temp
     end subroutine
-
-    #:for k1, t1 in BITSET_KINDS_TYPES
-    elemental subroutine swap_${k1}$(lhs,rhs)
-        use stdlib_bitsets
-        ${t1}$, intent(inout) :: lhs, rhs
-        ${t1}$ :: temp
-        temp = lhs ; lhs = rhs ; rhs = temp
-    end subroutine
-
-    #:endfor
     
 end module stdlib_math

From a72bca6fd909dfe642187e3d9788361341be821d Mon Sep 17 00:00:00 2001
From: jalvesz <102541118+jalvesz@users.noreply.github.com>
Date: Mon, 16 Sep 2024 17:47:24 +0200
Subject: [PATCH 12/15] Update src/stdlib_math.fypp

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>
---
 src/stdlib_math.fypp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index 49c63cd51..31ad628e9 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -553,7 +553,7 @@ contains
 
     elemental subroutine swap_str(lhs,rhs)
         character(*), intent(inout) :: lhs, rhs
-        character(len=max(len(lhs),len(rhs))) :: temp
+        character(len=:), allocatable :: temp
         temp = lhs ; lhs = rhs ; rhs = temp
     end subroutine
 

From 111996497a40fef5b2a5c5d65872518b62a5112d Mon Sep 17 00:00:00 2001
From: jalvesz <jose.alves@transvalor.com>
Date: Wed, 18 Sep 2024 20:18:38 +0200
Subject: [PATCH 13/15] add warning regarding swap on characters

---
 doc/specs/stdlib_math.md           |  7 +++++--
 example/math/example_math_swap.f90 | 13 +++++++++----
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/doc/specs/stdlib_math.md b/doc/specs/stdlib_math.md
index 8fa32084b..cfd632456 100644
--- a/doc/specs/stdlib_math.md
+++ b/doc/specs/stdlib_math.md
@@ -85,9 +85,12 @@ Elemental subroutine.
 `lhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character`, `string_type`, `bitset` type. This argument is `intent(inout)`.
 `rhs`: scalar or array of any of the intrinsic types `integer`, `real`, `complex`, `logical`, `character`, `string_type`, `bitset` type. This argument is `intent(inout)`.
 
-Note: All arguments must have same `type` and same `kind`.
+##### Note
+All arguments must have same `type` and same `kind`.
 
-#### Example
+**WARNING**: For fix size characters with different length, the `swap` subroutine will truncate the longest amongst `lhs` and `rhs`. To avoid truncation it is possible to pass a subsection of the string.
+
+#### Examples
 
 ```fortran
 {!example/math/example_math_swap.f90!}
diff --git a/example/math/example_math_swap.f90 b/example/math/example_math_swap.f90
index 8a34853c8..7c2388b05 100644
--- a/example/math/example_math_swap.f90
+++ b/example/math/example_math_swap.f90
@@ -24,10 +24,15 @@ program example_math_swap
     end block
 
     block
-        character(5) :: x, y
-        x = 'abcde'
-        y = 'fghij'
-        call swap(x,y)
+        character(4) :: x
+        character(6) :: y
+        x = 'abcd'
+        y = 'efghij'
+        call swap(x,y)      ! x=efgh,  y=abcd
+
+        x = 'abcd'
+        y = 'efghij'
+        call swap(x,y(1:4)) ! x=efgh,  y=abcdij
     end block
 
     block

From 775c8b44f8cf0de7fc4a9d1799247a70ea8ab2f2 Mon Sep 17 00:00:00 2001
From: jalvesz <102541118+jalvesz@users.noreply.github.com>
Date: Wed, 18 Sep 2024 20:19:10 +0200
Subject: [PATCH 14/15] Update src/stdlib_math.fypp

Co-authored-by: Sebastian Ehlert <28669218+awvwgk@users.noreply.github.com>
---
 src/stdlib_math.fypp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/stdlib_math.fypp b/src/stdlib_math.fypp
index 31ad628e9..1b1abb363 100644
--- a/src/stdlib_math.fypp
+++ b/src/stdlib_math.fypp
@@ -553,7 +553,7 @@ contains
 
     elemental subroutine swap_str(lhs,rhs)
         character(*), intent(inout) :: lhs, rhs
-        character(len=:), allocatable :: temp
+        character(len=max(len(lhs), len(rhs))) :: temp
         temp = lhs ; lhs = rhs ; rhs = temp
     end subroutine
 

From 7c5763c2b8fa4de5faa1898891366cb9551b2c0d Mon Sep 17 00:00:00 2001
From: jalvesz <jose.alves@transvalor.com>
Date: Sat, 21 Sep 2024 12:35:10 +0200
Subject: [PATCH 15/15] add test for strings with different lengths

---
 test/math/test_stdlib_math.fypp | 55 ++++++++++++++++++++++++---------
 1 file changed, 40 insertions(+), 15 deletions(-)

diff --git a/test/math/test_stdlib_math.fypp b/test/math/test_stdlib_math.fypp
index 834b2f1dd..1365756b9 100644
--- a/test/math/test_stdlib_math.fypp
+++ b/test/math/test_stdlib_math.fypp
@@ -304,23 +304,48 @@ contains
 
     subroutine test_swap_str(error)
         type(error_type), allocatable, intent(out) :: error
-        character(5) :: x(2), y(2)
-        
-        x = ['abcde','fghij'] 
-        y = ['fghij','abcde']
+        block
+            character(5) :: x(2), y(2)
+            
+            x = ['abcde','fghij'] 
+            y = ['fghij','abcde']
 
-        call swap(x,y)
-        
-        call check(error, all( x == ['fghij','abcde'] ) )
-        if (allocated(error)) return
-        call check(error, all( y == ['abcde','fghij']  ) )
-        if (allocated(error)) return
+            call swap(x,y)
+            
+            call check(error, all( x == ['fghij','abcde'] ) )
+            if (allocated(error)) return
+            call check(error, all( y == ['abcde','fghij']  ) )
+            if (allocated(error)) return
 
-        ! check self swap
-        call swap(x,x)
-        
-        call check(error, all( x == ['fghij','abcde'] ) )
-        if (allocated(error)) return
+            ! check self swap
+            call swap(x,x)
+            
+            call check(error, all( x == ['fghij','abcde'] ) )
+            if (allocated(error)) return
+        end block
+
+        block
+            character(4) :: x
+            character(6) :: y
+            
+            x = 'abcd'
+            y = 'efghij'
+            call swap(x,y)
+            
+            call check(error, x == 'efgh' )
+            if (allocated(error)) return
+            call check(error, y(1:6) == 'abcd  ' )
+            if (allocated(error)) return
+
+            x = 'abcd'
+            y = 'efghij'
+            call swap(x,y(1:4))
+            
+            call check(error, x == 'efgh' )
+            if (allocated(error)) return
+            call check(error, y == 'abcdij' )
+            if (allocated(error)) return
+        end block
     end subroutine test_swap_str
 
     subroutine test_swap_stt(error)