diff --git a/libraries/Adler/.arduino-ci.yml b/libraries/Adler/.arduino-ci.yml
index a6382323..5ad41716 100644
--- a/libraries/Adler/.arduino-ci.yml
+++ b/libraries/Adler/.arduino-ci.yml
@@ -2,13 +2,13 @@ compile:
   # Choosing to run compilation tests on 2 different Arduino platforms
   platforms:
     - uno
-    # - due
-    # - zero
-    # - leonardo
+    - due
+    - zero
+    - leonardo
     - m4
     - esp32
-    # - esp8266
-    # - mega2560
+    - esp8266
+    - mega2560
 
   libraries:
     - "printHelpers"
diff --git a/libraries/Adler/Adler.cpp b/libraries/Adler/Adler.cpp
index 2719d288..81c50516 100644
--- a/libraries/Adler/Adler.cpp
+++ b/libraries/Adler/Adler.cpp
@@ -1,158 +1,17 @@
 //
 //    FILE: Adler.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.1.2
+// VERSION: 0.2.0
 //    DATE: 2022-01-27
-// PURPOSE: Arduino Library for calculating Adler-32 checksum
+// PURPOSE: Arduino Library for calculating Adler checksum
 //     URL: https://github.com/RobTillaart/Adler
 //          https://en.wikipedia.org/wiki/Adler-32
-//
-//  HISTORY
-//  0.1.0   2022-01-27   initial version
-//  0.1.1   2022-04-15   split of .cpp file
-//  0.1.2   2022-06-13   split interface and implementation
-//                       rename ADLER32_MOD_PRIME
-//                       rename ADLER32_LIB_VERSION
-//                       add addFast(array, length)
-//                       add char interfaces
+//          (no Adler16 reference, implementation is experimental)
 
 
 #include "Adler.h"
 
 
-Adler32::Adler32()
-{
-  begin(1, 0);
-}
-
-
-void Adler32::begin(uint32_t s1, uint32_t s2)
-{
-  _s1 = s1;
-  _s2 = s2;
-  _count = 0;
-}
-
-
-//  reference implementation
-void Adler32::add(uint8_t value)
-{
-  _count++;
-  _s1 += value;
-   if (_s1 >= ADLER32_MOD_PRIME) _s1 -= ADLER32_MOD_PRIME;
-  _s2 += _s1;
-   if (_s2 >= ADLER32_MOD_PRIME) _s2 -= ADLER32_MOD_PRIME;
-}
-
-
-//  optimized version (~10% gain)
-//  void Adler32::add(uint8_t value)
-//  {
-//    _count++;
-//    _s1 += value;
-//    _s2 += _s1;
-//     if (_s2 >= ADLER32_MOD_PRIME)
-//     {
-//       _s2 -= ADLER32_MOD_PRIME;
-//       if (_s1 >= ADLER32_MOD_PRIME) _s1 -= ADLER32_MOD_PRIME;
-//     }
-//  }
-
-
-//  straightforward going through the array.
-void Adler32::add(uint8_t * array, uint16_t length)
-{
-  while (length--)
-  {
-    add(*array++);
-  }
-  return;
-}
-
-
-//  optimized version (under test)
-//  S1 grows linear
-//  S2 grows quadratic
-//  as S2 grows faster than S1, S1 needs only to be checked 
-//     if S2 hits the ADLER32_MOD_PRIME and probably far less.
-//
-//  void Adler32::addFast(uint8_t * array, uint16_t length)
-//  {
-//    _count += length;
-//    while (length--)
-//    {
-//      _s1 += *array++;
-//      _s2 += _s1;
-//      if (_s2 >= ADLER32_MOD_PRIME)
-//      {
-//        _s2 -= ADLER32_MOD_PRIME;
-//        if (_s1 >= ADLER32_MOD_PRIME)
-//        {
-//          _s1 -= ADLER32_MOD_PRIME;
-//        }
-//      }
-//    }
-//  }
-
-
-//  further optimized version (under test)
-//  S1 grows linear
-//  S2 grows quadratic
-//  only do modulo when we reach halfway uint32_t
-//  or when really needed.
-void Adler32::addFast(uint8_t * array, uint16_t length)
-{
-  _count += length;
-  uint32_t s1 = _s1;
-  uint32_t s2 = _s2;
-  for (uint16_t i = 0; i < length;)
-  {
-    // if S2 is halfway it is time to do modulo
-    while ((i < length) && (s2 < 2147483648ULL))
-    {
-      s1 += array[i++];
-      s2 += s1;
-    }
-    if (s2 >= ADLER32_MOD_PRIME)
-    {
-      s2 %= ADLER32_MOD_PRIME;
-      if (s1 >= ADLER32_MOD_PRIME) s1 %= ADLER32_MOD_PRIME;
-    }
-  }
-  _s1 = s1;
-  _s2 = s2;
-}
-
-
-//////////////////////////////////////////////////////////////
-//
-//  wrapper for strings.
-//
-void Adler32::add(char value)
-{
-  add((uint8_t) value);
-}
-
-
-void Adler32::add(char * array, uint16_t length)
-{
-  add((uint8_t *) array, length);
-}
-
-
-void Adler32::addFast(char * array, uint16_t length)
-{
-  addFast((uint8_t *) array, length);
-}
-
-
-uint32_t Adler32::getAdler()
-{
-  return (_s2 << 16) | _s1;
-};
-
-
-
 //////////////////////////////////////////////////////////////
 //
 //  STATIC FUNCTION
@@ -176,5 +35,24 @@ uint32_t adler32(uint8_t * array, uint16_t length)
 }
 
 
+uint16_t adler16(uint8_t * array, uint16_t length)
+{
+  uint16_t s1 = 1;
+  uint16_t s2 = 0;
+  for (uint16_t i = 0; i < length;)
+  {
+    // if S2 is halfway it is time to do modulo
+    while ((i < length) && (s2 < 32768))
+    {
+      s1 += array[i++];
+      s2 += s1;
+    }
+    s1 %= ADLER16_MOD_PRIME;
+    s2 %= ADLER16_MOD_PRIME;
+  }
+  return (s2 << 8) | s1;
+}
+
+
 // -- END OF FILE -- 
 
diff --git a/libraries/Adler/Adler.h b/libraries/Adler/Adler.h
index 1ec4368f..7257b8fb 100644
--- a/libraries/Adler/Adler.h
+++ b/libraries/Adler/Adler.h
@@ -2,9 +2,9 @@
 //
 //    FILE: Adler.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.1.2
+// VERSION: 0.2.0
 //    DATE: 2022-01-27
-// PURPOSE: Arduino Library for calculating Adler-32 checksum
+// PURPOSE: Arduino Library for calculating Adler checksum
 //     URL: https://github.com/RobTillaart/Adler
 //          https://en.wikipedia.org/wiki/Adler-32
 
@@ -12,11 +12,11 @@
 #include "Arduino.h"
 
 
-#define ADLER32_LIB_VERSION        (F("0.1.2"))
+#define ADLER_LIB_VERSION        (F("0.2.0"))
 
 
-const uint16_t ADLER32_MOD_PRIME = 65521;
-
+const uint32_t ADLER32_MOD_PRIME = 65521;
+const uint16_t ADLER16_MOD_PRIME = 251;
 
 
 /////////////////////////////////////////////////
@@ -24,39 +24,7 @@ const uint16_t ADLER32_MOD_PRIME = 65521;
 //  STATIC FUNCTIONS
 //
 uint32_t adler32(uint8_t *data, uint16_t length);
-
-
-
-/////////////////////////////////////////////////
-//
-//  CLASS VERSION
-//
-class Adler32
-{
-public:
-  Adler32();
-
-  void begin(uint32_t s1 = 1, uint32_t s2 = 0);
-
-  void add(uint8_t value);
-  void add(uint8_t * array, uint16_t length);
-  //  trade PROGMEM for speed
-  void addFast(uint8_t * array, uint16_t length);
-
-  //  wrappers for strings
-  void add(char value);
-  void add(char * array, uint16_t length);
-  void addFast(char * array, uint16_t length);
-
-
-  uint32_t getAdler();
-  uint32_t count() { return _count; };
-
-private:
-  uint32_t _s1;
-  uint32_t _s2;
-  uint32_t _count;
-};
+uint16_t adler16(uint8_t *data, uint16_t length);
 
 
 // -- END OF FILE -- 
diff --git a/libraries/Adler/Adler16.cpp b/libraries/Adler/Adler16.cpp
new file mode 100644
index 00000000..1d8d397b
--- /dev/null
+++ b/libraries/Adler/Adler16.cpp
@@ -0,0 +1,127 @@
+//
+//    FILE: Adler16.cpp
+//  AUTHOR: Rob Tillaart
+// VERSION: 0.2.0
+//    DATE: 2022-06-14
+// PURPOSE: Arduino Library for calculating Adler-16 checksum
+//     URL: https://github.com/RobTillaart/Adler
+//          https://en.wikipedia.org/wiki/Adler-32
+//          (no Adler16 reference, implementation is experimental)
+//
+// HISTORY: see CHANGELOG.md
+
+
+
+#include "Adler16.h"
+
+
+Adler16::Adler16()
+{
+  begin(1, 0);
+}
+
+
+void Adler16::begin(uint16_t s1, uint16_t s2)
+{
+  _s1 = s1;
+  _s2 = s2;
+  _count = 0;
+}
+
+
+//  reference implementation
+// void Adler16::add(uint8_t value)
+// {
+  // _count++;
+  // _s1 += value;
+   // if (_s1 >= ADLER16_MOD_PRIME) _s1 -= ADLER16_MOD_PRIME;
+  // _s2 += _s1;
+   // if (_s2 >= ADLER16_MOD_PRIME) _s2 -= ADLER16_MOD_PRIME;
+// }
+
+
+//  optimized version (~10% faster)
+void Adler16::add(uint8_t value)
+{
+  _count++;
+  _s1 += value;
+  _s2 += _s1;
+  if (_s2 >= ADLER16_MOD_PRIME)
+  {
+    _s2 -= ADLER16_MOD_PRIME;
+    if (_s1 >= ADLER16_MOD_PRIME) _s1 -= ADLER16_MOD_PRIME;
+  }
+}
+
+
+//  straightforward going through the array.
+//  small footprint
+void Adler16::add(uint8_t * array, uint16_t length)
+{
+  while (length--)
+  {
+    add(*array++);
+  }
+  return;
+}
+
+
+//  Optimized version
+//  S1 grows linear
+//  S2 grows quadratic
+//  only do modulo when S2 reaches halfway uint16_t
+//                      and at the end of the loop.
+void Adler16::addFast(uint8_t * array, uint16_t length)
+{
+  _count += length;
+  uint16_t s1 = _s1;
+  uint16_t s2 = _s2;
+  for (uint16_t i = 0; i < length;)
+  {
+    // if S2 is halfway it is time to do modulo
+    while ((i < length) && (s2 < 32768))
+    {
+      s1 += array[i++];
+      s2 += s1;
+    }
+    if (s2 >= ADLER16_MOD_PRIME)
+    {
+      s2 %= ADLER16_MOD_PRIME;
+      if (s1 >= ADLER16_MOD_PRIME) s1 %= ADLER16_MOD_PRIME;
+    }
+  }
+  _s1 = s1;
+  _s2 = s2;
+}
+
+
+uint16_t Adler16::getAdler()
+{
+  return (_s2 << 8) | _s1;
+};
+
+
+//////////////////////////////////////////////////////////////
+//
+//  wrappers for strings.
+//
+void Adler16::add(char value)
+{
+  add((uint8_t) value);
+}
+
+
+void Adler16::add(char * array, uint16_t length)
+{
+  add((uint8_t *) array, length);
+}
+
+
+void Adler16::addFast(char * array, uint16_t length)
+{
+  addFast((uint8_t *) array, length);
+}
+
+
+// -- END OF FILE --
+
diff --git a/libraries/Adler/Adler16.h b/libraries/Adler/Adler16.h
new file mode 100644
index 00000000..26326de1
--- /dev/null
+++ b/libraries/Adler/Adler16.h
@@ -0,0 +1,52 @@
+#pragma once
+//
+//    FILE: Adler16.cpp
+//  AUTHOR: Rob Tillaart
+// VERSION: 0.2.0
+//    DATE: 2022-06-15
+// PURPOSE: Arduino Library for calculating Adler-16 checksum
+//     URL: https://github.com/RobTillaart/Adler
+//          https://en.wikipedia.org/wiki/Adler-32  
+//          (no Adler16 reference, implementation is experimental)
+
+
+#include "Arduino.h"
+
+
+#define ADLER16_LIB_VERSION              (F("0.2.0"))
+
+
+//  largest prime below 2^8
+const uint16_t ADLER16_MOD_PRIME = 251;
+
+class Adler16
+{
+public:
+  Adler16();
+
+  void begin(uint16_t s1 = 1, uint16_t s2 = 0);
+
+  void add(uint8_t value);
+  void add(uint8_t * array, uint16_t length);
+  //  trade PROGMEM for speed
+  void addFast(uint8_t * array, uint16_t length);
+
+  //  wrappers for strings
+  void add(char value);
+  void add(char * array, uint16_t length);
+  void addFast(char * array, uint16_t length);
+
+
+  uint16_t getAdler();
+  uint16_t count() { return _count; };
+
+private:
+  uint16_t _s1;
+  uint16_t _s2;
+  uint32_t _count;
+};
+
+
+// -- END OF FILE -- 
+
+
diff --git a/libraries/Adler/Adler32.cpp b/libraries/Adler/Adler32.cpp
new file mode 100644
index 00000000..5ca98bcc
--- /dev/null
+++ b/libraries/Adler/Adler32.cpp
@@ -0,0 +1,127 @@
+//
+//    FILE: Adler32.cpp
+//  AUTHOR: Rob Tillaart
+// VERSION: 0.2.0
+//    DATE: 2022-01-27
+// PURPOSE: Arduino Library for calculating Adler-32 checksum
+//     URL: https://github.com/RobTillaart/Adler
+//          https://en.wikipedia.org/wiki/Adler-32
+//
+// HISTORY: see CHANGELOG.md
+
+
+
+#include "Adler32.h"
+
+
+Adler32::Adler32()
+{
+  begin(1, 0);
+}
+
+
+void Adler32::begin(uint32_t s1, uint32_t s2)
+{
+  _s1 = s1;
+  _s2 = s2;
+  _count = 0;
+}
+
+
+//  reference implementation
+// void Adler32::add(uint8_t value)
+// {
+  // _count++;
+  // _s1 += value;
+   // if (_s1 >= ADLER32_MOD_PRIME) _s1 -= ADLER32_MOD_PRIME;
+  // _s2 += _s1;
+   // if (_s2 >= ADLER32_MOD_PRIME) _s2 -= ADLER32_MOD_PRIME;
+// }
+
+
+//  optimized version (~10% faster)
+void Adler32::add(uint8_t value)
+{
+  _count++;
+  _s1 += value;
+  _s2 += _s1;
+  if (_s2 >= ADLER32_MOD_PRIME)
+  {
+    _s2 -= ADLER32_MOD_PRIME;
+    if (_s1 >= ADLER32_MOD_PRIME) _s1 -= ADLER32_MOD_PRIME;
+  }
+}
+
+
+//  straightforward going through the array.
+//  small footprint.
+void Adler32::add(uint8_t * array, uint16_t length)
+{
+  while (length--)
+  {
+    add(*array++);
+  }
+  return;
+}
+
+
+//  Optimized version
+//  S1 grows linear
+//  S2 grows quadratic
+//  only do modulo when S2 reaches halfway uint32_t
+//                      and at the end of the loop.
+void Adler32::addFast(uint8_t * array, uint16_t length)
+{
+  _count += length;
+  uint32_t s1 = _s1;
+  uint32_t s2 = _s2;
+  for (uint16_t i = 0; i < length;)
+  {
+    // if S2 is halfway it is time to do modulo
+    while ((i < length) && (s2 < 2147483648ULL))
+    {
+      s1 += array[i++];
+      s2 += s1;
+    }
+    if (s2 >= ADLER32_MOD_PRIME)
+    {
+      s2 %= ADLER32_MOD_PRIME;
+      if (s1 >= ADLER32_MOD_PRIME) s1 %= ADLER32_MOD_PRIME;
+    }
+  }
+  _s1 = s1;
+  _s2 = s2;
+}
+
+
+uint32_t Adler32::getAdler()
+{
+  return (_s2 << 16) | _s1;
+};
+
+
+
+//////////////////////////////////////////////////////////////
+//
+//  wrappers for strings.
+//
+void Adler32::add(char value)
+{
+  add((uint8_t) value);
+}
+
+
+void Adler32::add(char * array, uint16_t length)
+{
+  add((uint8_t *) array, length);
+}
+
+
+void Adler32::addFast(char * array, uint16_t length)
+{
+  addFast((uint8_t *) array, length);
+}
+
+
+// -- END OF FILE --
+
diff --git a/libraries/Adler/Adler32.h b/libraries/Adler/Adler32.h
new file mode 100644
index 00000000..aebb0181
--- /dev/null
+++ b/libraries/Adler/Adler32.h
@@ -0,0 +1,52 @@
+#pragma once
+//
+//    FILE: Adler.h
+//  AUTHOR: Rob Tillaart
+// VERSION: 0.2.0
+//    DATE: 2022-01-27
+// PURPOSE: Arduino Library for calculating Adler-32 checksum
+//     URL: https://github.com/RobTillaart/Adler
+//          https://en.wikipedia.org/wiki/Adler-32
+
+
+#include "Arduino.h"
+
+
+#define ADLER32_LIB_VERSION        (F("0.2.0"))
+
+
+//  largest prime below 2^16
+const uint32_t ADLER32_MOD_PRIME = 65521;
+
+
+class Adler32
+{
+public:
+  Adler32();
+
+  void begin(uint32_t s1 = 1, uint32_t s2 = 0);
+
+  void add(uint8_t value);
+  void add(uint8_t * array, uint16_t length);
+  //  trade PROGMEM for speed
+  void addFast(uint8_t * array, uint16_t length);
+
+  //  wrappers for strings
+  void add(char value);
+  void add(char * array, uint16_t length);
+  void addFast(char * array, uint16_t length);
+
+
+  uint32_t getAdler();
+  uint32_t count() { return _count; };
+
+private:
+  uint32_t _s1;
+  uint32_t _s2;
+  uint32_t _count;
+};
+
+
+// -- END OF FILE -- 
+
+
diff --git a/libraries/Adler/CHANGELOG.md b/libraries/Adler/CHANGELOG.md
new file mode 100644
index 00000000..8505120e
--- /dev/null
+++ b/libraries/Adler/CHANGELOG.md
@@ -0,0 +1,34 @@
+# Change Log
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](http://keepachangelog.com/)
+and this project adheres to [Semantic Versioning](http://semver.org/).
+
+## [0.2.0] - 2022-06-15
+
+- breaking change 
+- reordering files.
+- Adler.h for static functions
+- Adler32.h for Adler32 class
+- Adler16.h for Adler16 class (experimental).
+- Added optimizations.
+
+## [0.1.2] - 2022-06-13
+
+- split interface and implementation
+- rename ADLER32_MOD_PRIME
+- rename ADLER32_LIB_VERSION
+- add addFast(array, length)
+- add char interfaces
+
+## [0.1.1] - 2022-04-15
+
+- split of .cpp file
+
+### [0.1.0] - 2022-01-27
+
+- initial version
+
+
+
diff --git a/libraries/Adler/README.md b/libraries/Adler/README.md
index d0e70782..d21f7748 100644
--- a/libraries/Adler/README.md
+++ b/libraries/Adler/README.md
@@ -8,12 +8,16 @@
 
 # Adler
 
-Arduino Library for Adler-32 checksum
+Arduino Library for Adler-32 and experimental Adler-16 checksum.
 
 
 ## Description
 
-This library provides a Adler checksum of a data array.
+This library provides a Adler32 checksum of a data array.
+Furthermore since 0.2.0 an experimental Adler-16 implementation is added.
+This one is often faster as it uses a smaller checksum than the Adler32,
+and the price is that it is less sensitive than the Adler32.
+Still it might have its niches where it will be useful.
 
 Relates to https://github.com/RobTillaart/CRC
 
@@ -21,13 +25,21 @@ Relates to https://github.com/RobTillaart/Fletcher
 
 Tested on Arduino UNO only.
 
+0.2.0 is a breaking change, file names have been changed to be more
+in line with the CRC library.
+- Adler.h for the static functions
+- Adler32.h for the Adler32 class
+- Adler16.h for the Adler16 class.
+
 
 ## Interface
 
 
-## Adler class
+### Adler class
 
-Use **\#include "Adler.h"**
+Use **\#include "Adler32.h"** or **\#include "Adler16.h"**
+
+The interface for the Adler16 is very similar. 
 
 - **Adler32()** Constructor, initializes internals.
 - **void begin(uint8_t s1 = 1, uint8_t s2 = 0)** resets the internals.
@@ -43,58 +55,142 @@ The class is typically used for streaming very large blocks of data,
 optional with intermediate checksum tests.
 
 
-#### Performance
+## Performance Adler32
 
 Not tested ESP32 (and many other platforms) yet.
-First numbers of **.add(value)** measured with test sketch shows the following timing.
 
-| Version | Checksum |  UNO 16 MHz  |  ESP32 240 MHz  |
-|:-------:|:---------|:------------:|:---------------:|
-| 0.1.0   | Adler32  |     5.6 us   |                 |
-| 0.1.2   | Adler32  |     6.6 us   |                 |
-
-Todo elaborate / investigate.
+Numbers measured with **Adler32_performance.ino**.
 
 
-#### Performance 2
+### add(value)
 
-(since 0.1.2) 
+The **add(value)** adds one byte and does a subtraction
+instead of a modulo.
 
-The **addFast(array, length)** is faster than the reference **add(array, length)** but uses 108 bytes more, so a slightly larger footprint. 
-So depending on your needs, you choose performance or footprint. 
+| Version | Function | UNO 16 MHz | ESP32 240 MHz |
+|:-------:|:---------|:----------:|:-------------:|
+| 0.1.0   | add      |   5.6 us   |               |
+| 0.1.2   | add      |   6.6 us   |               |
+| 0.2.0   | add      |   5.9 us   |               |
+
+
+### add(lorem) 868 chars
+
+The **add(array, length)** is a straightforward loop
+over the array and has a small footprint.
+
+| Version | Function | UNO 16 MHz | ESP32 240 MHz |
+|:-------:|:---------|:----------:|:-------------:|
+| 0.1.0   | add      |            |               |
+| 0.1.2   | add      |  6392 us   |               |
+| 0.2.0   | add      |  5748 us   |               |
+
+Note: **add()** is about 6.6 us per byte.
+
+
+### addFast(lorem) 868 chars
+
+The **addFast(array, length)** is faster than the 
+reference **add(array, length)** and uses 108 bytes more.
+So the function has a larger footprint. 
+Depending on your needs, choose performance or footprint. 
 
 See **Adler32_performance_addFast.ino**
 
 
+| Version | Function | UNO 16 MHz | ESP32 240 MHz |
+|:-------:|:---------|:----------:|:-------------:|
+| 0.1.0   | addFast  |            |               |
+| 0.1.2   | addFast  |  1348 us   |               |
+| 0.2.0   | addFast  |  1348 us   |               |
+
+Note: **addFast()** is less than 2 us per byte.
+
+
+
+## Performance Adler16
+
+Not tested ESP32 (and many other platforms) yet.
+
+Numbers measured with **Adler16_performance.ino**.
+
+
+### add(value)
+
+The **add(value)** adds one byte and does a subtraction
+instead of a modulo.
+
+| Version | Function | UNO 16 MHz | ESP32 240 MHz |
+|:-------:|:---------|:----------:|:-------------:|
+| 0.2.0   | add      |   4.0 us   |               |
+
+The per byte performance of the Adler16 (on UNO) is faster 
+than the Adler32 **add(value)**. The reason is that a 16 bit 
+subtraction on an UNO is faster than a 32 bit subtraction.
+
+
+### add(lorem) 868 chars
+
+The **add(array, length)** is a straightforward loop
+over the array and has a small footprint.
+
+| Version | Function | UNO 16 MHz | ESP32 240 MHz |
+|:-------:|:---------|:----------:|:-------------:|
+| 0.2.0   | add      |  4040 us   |               |
+
+Note: **add()** is about 6.6 us per byte.
+
+
+### addFast(lorem) 868 chars
+
+The **addFast(array, length)** is faster than the 
+reference **add(array, length)**.
+
+| Version | Function | UNO 16 MHz | ESP32 240 MHz |
+|:-------:|:---------|:----------:|:-------------:|
+| 0.2.0   | addFast  |  1968 us   |               |
+
+The gain of the faster 16 bit modulo meets the frequency of
+doing the modulo more often.
+
 
 ## Interface static functions
 
-The function is straightforward.
+The functions are straightforward.
 
 Use **\#include "Adler.h"**
 
 - **uint32_t adler32(uint8_t \*data, uint16_t length)** length in units of 1 byte = 8 bits.
+- **uint16_t adler16(uint8_t \*data, uint16_t length)** length in units of 1 byte = 8 bits.
 
-The function is typically used for an in memory buffer to calculate 
-the Adler checksum once.
+The functions are typically used for an in memory buffer to calculate the checksum once. 
+Think of packets in a network, records in a database, or a checksum for an configuration in EEPROM.
 
 
-#### Performance
+### Performance
 
+Not tested ESP32 (and many other platforms) yet.
 
-Not tested extensively, first numbers of **.add(array, length)**
-measured with **Adler_performance.ino** sketch shows the following timing.
+Numbers measured with **Adler_performance.ino**.
 
 Lorem Ipsum text = 868 bytes.
 
-| Checksum    |  UNO 16 MHz | ESP32 240 MHz |
-|:------------|:-----------:|:-------------:|
-| Adler32     |   1116 us   |               |
-
-Average 1116 / 868 = 1.29 us per byte.
+| Version | Function | UNO 16 MHz | ESP32 240 MHz |
+|:-------:|:---------|:----------:|:-------------:|
+| 0.1.0   | Adler32  |  1116 us   |               |
+| 0.1.2   | Adler32  |  1116 us   |               |
+| 0.2.0   | Adler32  |  1116 us   |               |
+| 0.2.0   | Adler16  |  1736 us   |               |
 
 
+Adler32 average 1116 / 868 = 1.29 us per byte.
+Adler16 average 1736 / 868 = 2.00 us per byte. (~1.5x slower !)
 
+Adler16 does more often the modulo math as it reaches halfway uint16_t 
+faster than Adler32 reaches halfway uint32_t.
+
+As the Adler16 is less performant as the Adler32, it is often the best to use
+the 32 bit version.
 
 
 ## Operation
@@ -104,9 +200,17 @@ See examples.
 
 ## Future
 
-- test other platforms
-- add Adler-16, similar algorithm 
-  - ADLER16_MOD_PRIME  32749 = largest prime below 2^15 (32768)
-  - (0.2.0)
+- return values for **add(array)** and **addFast(array)**
+  - updated checksum?
+  - not for **add(value)** as that would create quite some overhead.
+- Adler64 ?
+  - would need a large prime (which)
+
+
+#### Wont
+
+- do the string wrappers need strlen() ? parameter.
+  - yes, as string can be processed partially.
+
 
 
diff --git a/libraries/Adler/examples/Adler16_performance/Adler16_performance.ino b/libraries/Adler/examples/Adler16_performance/Adler16_performance.ino
new file mode 100644
index 00000000..718bdfe3
--- /dev/null
+++ b/libraries/Adler/examples/Adler16_performance/Adler16_performance.ino
@@ -0,0 +1,178 @@
+//
+//    FILE: Adler16_performance.ino
+//  AUTHOR: Rob Tillaart
+// PURPOSE: demo
+
+#include "Arduino.h"
+#include "Adler16.h"
+
+
+Adler16 ad;
+volatile uint8_t z;
+uint32_t start, stop, randomtime;
+
+char lorem[] = "Lorem ipsum dolor sit amet, \
+consectetuer adipiscing elit. Aenean commodo ligula eget dolor. \
+Aenean massa. Cum sociis natoque penatibus et magnis dis parturient \
+montes, nascetur ridiculus mus. Donec quam felis, ultricies nec, \
+pellentesque eu, pretium quis, sem. Nulla consequat massa quis enim. \
+Donec pede justo, fringilla vel, aliquet nec, vulputate eget, arcu. \
+In enim justo, rhoncus ut, imperdiet a, venenatis vitae, justo. \
+Nullam dictum felis eu pede mollis pretium. Integer tincidunt. \
+Cras dapibus. Vivamus elementum semper nisi. \
+Aenean vulputate eleifend tellus. Aenean leo ligula, porttitor eu, \
+consequat vitae, eleifend ac, enim. Aliquam lorem ante, dapibus in, \
+viverra quis, feugiat a, tellus. Phasellus viverra nulla ut metus \
+varius laoreet. Quisque rutrum. Aenean imperdiet. Etiam ultricies \
+nisi vel augue. Curabitur ullamcorper ultricies nisi. Nam eget dui.";
+
+
+char hello[] = "hello world";
+
+
+
+void setup()
+{
+  Serial.begin(115200);
+  while (!Serial);
+
+  Serial.println();
+  Serial.println("Adler16_performance");
+  Serial.print("ADLER16_LIB_VERSION: ");
+  Serial.println(ADLER16_LIB_VERSION);
+
+  start = micros();
+  for (uint16_t x = 0; x < 10000; x++)
+  {
+    z = random(255);
+  }
+  stop = micros();
+  randomtime = stop - start;
+  Serial.print("randomtime: ");
+  Serial.println(randomtime);
+  delay(100);
+
+  ad.begin();
+  start = micros();
+  for (uint16_t x = 0; x < 10000; x++)
+  {
+    z = random(255);
+    ad.add(z);
+  }
+  stop = micros();
+  Serial.print("     total: ");
+  Serial.println(stop - start);
+  Serial.print(" 1e4 x add: ");
+  Serial.println(stop - start - randomtime);
+  delay(100);
+
+  Serial.print("  checksum: ");
+  Serial.println(ad.getAdler());
+  Serial.println();
+  delay(100);
+
+  ad.begin();
+  start = micros();
+  for (uint32_t x = 0; x < 1000000; x++)
+  {
+    z = x & 0xFF;
+    ad.add(z);
+  }
+  stop = micros();
+  Serial.print("     total: ");
+  Serial.println(stop - start);
+  Serial.print(" 1e6 x add: ");
+  Serial.println(stop - start - randomtime);
+  delay(100);
+  Serial.print("  checksum: ");
+  Serial.println(ad.getAdler());
+  Serial.println();
+  delay(100);
+
+  /////////////////////////////////////////////////////////////////
+
+  ad.begin();
+  Serial.print("LENGTH LOREM: ");
+  Serial.println(strlen(lorem));
+  Serial.println();
+  delay(100);
+  start = micros();
+  for (int i = 0; lorem[i] != 0; i++)
+  {
+    ad.add(lorem[i]);
+  }
+  stop = micros();
+  Serial.print("   lorem 1: ");
+  Serial.print(stop - start);
+  Serial.print("\tchecksum: ");
+  Serial.println(ad.getAdler());
+  delay(100);
+
+  ad.begin();
+  start = micros();
+  ad.add(lorem, strlen(lorem));
+  stop = micros();
+  Serial.print("   lorem 2: ");
+  Serial.print(stop - start);
+  Serial.print("\tchecksum: ");
+  Serial.println(ad.getAdler());
+  delay(100);
+
+  ad.begin();
+  start = micros();
+  ad.addFast(lorem, strlen(lorem));
+  stop = micros();
+  Serial.print("   lorem 3: ");
+  Serial.print(stop - start);
+  Serial.print("\tchecksum: ");
+  Serial.println(ad.getAdler());
+  Serial.println();
+  delay(100);
+
+  /////////////////////////////////////////////////////////////////
+
+  ad.begin();
+  Serial.print("LENGTH HELLO: ");
+  Serial.println(strlen(hello));
+  Serial.println();
+  delay(100);
+  start = micros();
+  for (int i = 0; hello[i] != 0; i++)
+  {
+    ad.add(hello[i]);
+  }
+  stop = micros();
+  Serial.print("   hello 1: ");
+  Serial.print(stop - start);
+  Serial.print("\tchecksum: ");
+  Serial.println(ad.getAdler());
+  delay(100);
+
+  ad.begin();
+  start = micros();
+  ad.add(hello, strlen(hello));
+  stop = micros();
+  Serial.print("   hello 2: ");
+  Serial.print(stop - start);
+  Serial.print("\tchecksum: ");
+  Serial.println(ad.getAdler());
+  delay(100);
+
+  ad.begin();
+  start = micros();
+  ad.addFast(hello, strlen(hello));
+  stop = micros();
+  Serial.print("   hello 3: ");
+  Serial.print(stop - start);
+  Serial.print("\tchecksum: ");
+  Serial.println(ad.getAdler());
+  Serial.println();
+}
+
+
+void loop()
+{
+}
+
+
+// -- END OF FILE --
diff --git a/libraries/Adler/examples/Adler16_performance/Adler16_performance_0.1.0.txt b/libraries/Adler/examples/Adler16_performance/Adler16_performance_0.1.0.txt
new file mode 100644
index 00000000..a0814560
--- /dev/null
+++ b/libraries/Adler/examples/Adler16_performance/Adler16_performance_0.1.0.txt
@@ -0,0 +1,24 @@
+Adler16_performance
+ADLER16_LIB_VERSION: 0.1.0
+randomtime: 901476
+     total: 942656
+ 1e4 x add: 41180
+  checksum: 46478
+
+     total: 5157524
+ 1e6 x add: 4256048
+  checksum: 63140
+
+LENGTH LOREM: 868
+
+   lorem 1: 3792	checksum: 57303
+   lorem 2: 4224	checksum: 57303
+   lorem 3: 1972	checksum: 57303
+
+LENGTH HELLO: 11
+
+   hello 1: 52	checksum: 36209
+   hello 2: 60	checksum: 36209
+   hello 3: 48	checksum: 36209
+
+
diff --git a/libraries/Adler/examples/Adler16_performance/Adler16_performance_0.2.0.txt b/libraries/Adler/examples/Adler16_performance/Adler16_performance_0.2.0.txt
new file mode 100644
index 00000000..cc553f11
--- /dev/null
+++ b/libraries/Adler/examples/Adler16_performance/Adler16_performance_0.2.0.txt
@@ -0,0 +1,23 @@
+Adler16_performance
+ADLER16_LIB_VERSION: 0.2.0
+randomtime: 901476
+     total: 941076
+ 1e4 x add: 39600
+  checksum: 6798
+
+     total: 5000108
+ 1e6 x add: 4098632
+  checksum: 5028
+
+LENGTH LOREM: 868
+
+   lorem 1: 3600	checksum: 57303
+   lorem 2: 4040	checksum: 57303
+   lorem 3: 1968	checksum: 57303
+
+LENGTH HELLO: 11
+
+   hello 1: 48	checksum: 36209
+   hello 2: 56	checksum: 36209
+   hello 3: 48	checksum: 36209
+
diff --git a/libraries/Adler/examples/Adler16_test/Adler16_test.ino b/libraries/Adler/examples/Adler16_test/Adler16_test.ino
new file mode 100644
index 00000000..6fab3c60
--- /dev/null
+++ b/libraries/Adler/examples/Adler16_test/Adler16_test.ino
@@ -0,0 +1,52 @@
+//
+//    FILE: Adler16_test.ino
+//  AUTHOR: Rob Tillaart
+// PURPOSE: demo
+
+#include "Arduino.h"
+#include "Adler16.h"
+
+//  expected output
+//  Adler16_test
+//  ADLER16_LIB_VERSION: 0.2.0
+//  6012
+//  7293
+//  6269
+
+
+Adler16 ad;
+
+uint8_t arr1[5]  = { 100, 120, 130, 135, 140 };
+uint8_t arr2[5]  = { 101, 120, 130, 135, 140 };  // minimal diff.
+uint8_t arr3[5]  = { 100, 120, 130, 135, 141 };  // minimal diff.
+
+void setup()
+{
+  Serial.begin(115200);
+  while (!Serial);
+
+  Serial.println();
+  Serial.println("Adler16_test");
+  Serial.print("ADLER16_LIB_VERSION: ");
+  Serial.println(ADLER16_LIB_VERSION);
+
+  ad.begin();
+  ad.add(arr1, 5);
+  Serial.println(ad.getAdler());
+
+  ad.begin();
+  ad.add(arr2, 5);
+  Serial.println(ad.getAdler());
+
+  ad.begin();
+  ad.add(arr3, 5);
+  Serial.println(ad.getAdler());
+}
+
+
+void loop()
+{
+}
+
+
+// -- END OF FILE --
diff --git a/libraries/Adler/examples/Adler16_test/output_0.1.0.txt b/libraries/Adler/examples/Adler16_test/output_0.1.0.txt
new file mode 100644
index 00000000..0e1aeac6
--- /dev/null
+++ b/libraries/Adler/examples/Adler16_test/output_0.1.0.txt
@@ -0,0 +1,5 @@
+Adler16_test
+ADLER16_LIB_VERSION: 0.1.0
+7292
+8573
+7549
diff --git a/libraries/Adler/examples/Adler32_performance/Adler32_performance.ino b/libraries/Adler/examples/Adler32_performance/Adler32_performance.ino
index ce2b8c56..43e8e383 100644
--- a/libraries/Adler/examples/Adler32_performance/Adler32_performance.ino
+++ b/libraries/Adler/examples/Adler32_performance/Adler32_performance.ino
@@ -4,8 +4,7 @@
 // PURPOSE: demo
 
 #include "Arduino.h"
-#include "Adler.h"
-
+#include "Adler32.h"
 
 
 Adler32 ad;
diff --git a/libraries/Adler/examples/Adler32_performance/Adler32_performance_0.2.0.txt b/libraries/Adler/examples/Adler32_performance/Adler32_performance_0.2.0.txt
new file mode 100644
index 00000000..c4342bf9
--- /dev/null
+++ b/libraries/Adler/examples/Adler32_performance/Adler32_performance_0.2.0.txt
@@ -0,0 +1,24 @@
+Adler32_performance
+ADLER32_LIB_VERSION: 0.2.0
+randomtime: 901476
+     total: 960236
+ 1e4 x add: 58760
+  checksum: 1607808947
+
+     total: 6919548
+ 1e6 x add: 6018072
+  checksum: 237492440
+
+LENGTH LOREM: 868
+
+   lorem 1: 5308	checksum: 3972480156
+   lorem 2: 5748	checksum: 3972480156
+   lorem 3: 1348	checksum: 3972480156
+
+LENGTH HELLO: 11
+
+   hello 1: 64	checksum: 436929629
+   hello 2: 80	checksum: 436929629
+   hello 3: 32	checksum: 436929629
+
+
diff --git a/libraries/Adler/examples/Adler32_performance_addFast/Adler32_performance_addFast.ino b/libraries/Adler/examples/Adler32_performance_addFast/Adler32_performance_addFast.ino
index 6889aa52..0d1f9869 100644
--- a/libraries/Adler/examples/Adler32_performance_addFast/Adler32_performance_addFast.ino
+++ b/libraries/Adler/examples/Adler32_performance_addFast/Adler32_performance_addFast.ino
@@ -4,7 +4,7 @@
 // PURPOSE: demo
 
 #include "Arduino.h"
-#include "Adler.h"
+#include "Adler32.h"
 
 
 
@@ -31,7 +31,6 @@ nisi vel augue. Curabitur ullamcorper ultricies nisi. Nam eget dui.";
 char hello[] = "hello world";
 
 
-
 void setup()
 {
   Serial.begin(115200);
diff --git a/libraries/Adler/examples/Adler32_test/Adler32_test.ino b/libraries/Adler/examples/Adler32_test/Adler32_test.ino
index 664c0a60..eb203ee7 100644
--- a/libraries/Adler/examples/Adler32_test/Adler32_test.ino
+++ b/libraries/Adler/examples/Adler32_test/Adler32_test.ino
@@ -4,10 +4,11 @@
 // PURPOSE: demo
 
 #include "Arduino.h"
-#include "Adler.h"
+#include "Adler32.h"
 
 //  expected output
 //  Adler32_test
+//  ADLER32_LIB_VERSION: 0.2.0
 //  116982386
 //  117310067
 //  117047923
@@ -27,7 +28,9 @@ void setup()
 
   Serial.println();
   Serial.println("Adler32_test");
-
+  Serial.print("ADLER32_LIB_VERSION: ");
+  Serial.println(ADLER32_LIB_VERSION);
+  
   ad.begin();
   ad.add(arr1, 5);
   Serial.println(ad.getAdler());
diff --git a/libraries/Adler/examples/Adler_performance/Adler_performance.ino b/libraries/Adler/examples/Adler_performance/Adler_performance.ino
index fbc35def..fa6f4989 100644
--- a/libraries/Adler/examples/Adler_performance/Adler_performance.ino
+++ b/libraries/Adler/examples/Adler_performance/Adler_performance.ino
@@ -30,8 +30,8 @@ void setup()
   while (!Serial);
 
   Serial.println();
-  Serial.print("ADLER32_LIB_VERSION: ");
-  Serial.println(ADLER32_LIB_VERSION);
+  Serial.print("ADLER_LIB_VERSION: ");
+  Serial.println(ADLER_LIB_VERSION);
 
   for (int i = 0; i < 60; i++)
   {
@@ -53,6 +53,18 @@ void setup()
   Serial.print(x);
   Serial.print("\t");
   Serial.println(x, HEX);
+  delay(200);
+
+
+  start = micros();
+  volatile uint16_t y = adler16((uint8_t *) str, len);
+  stop = micros();
+  Serial.print("   TIME us: ");
+  Serial.println(stop - start);
+  Serial.print("  ADLER-16: ");
+  Serial.print(y);
+  Serial.print("\t");
+  Serial.println(y, HEX);
   delay(100);
 }
 
diff --git a/libraries/Adler/examples/Adler_test/Adler_test.ino b/libraries/Adler/examples/Adler_test/Adler_test.ino
index 2f0bfaf6..07f087c1 100644
--- a/libraries/Adler/examples/Adler_test/Adler_test.ino
+++ b/libraries/Adler/examples/Adler_test/Adler_test.ino
@@ -9,13 +9,20 @@
 
 
 //  expected output
-//  ADLER32_LIB_VERSION: 0.1.2
+//  ADLER_LIB_VERSION: 0.2.0
+//
+//  E1F5
+//  4660
+//  4634
+//  40A7
+//
 //  5C801F0
 //  81E0256
 //  E000325
 //  11E60398
 
 
+
 char str1[24] = "abcde";
 char str2[24] = "abcdef";
 char str3[24] = "abcdefgh";
@@ -28,13 +35,21 @@ void setup()
   while (!Serial);
 
   Serial.println();
-  Serial.print("ADLER32_LIB_VERSION: ");
-  Serial.println(ADLER32_LIB_VERSION);
+  Serial.print("ADLER_LIB_VERSION: ");
+  Serial.println(ADLER_LIB_VERSION);
+  Serial.println();
+
+  Serial.println(adler16((uint8_t *) str1, 5), HEX);
+  Serial.println(adler16((uint8_t *) str2, 6), HEX);
+  Serial.println(adler16((uint8_t *) str3, 8), HEX);
+  Serial.println(adler16((uint8_t *) str4, 9), HEX);
+  Serial.println();
 
   Serial.println(adler32((uint8_t *) str1, 5), HEX);
   Serial.println(adler32((uint8_t *) str2, 6), HEX);
   Serial.println(adler32((uint8_t *) str3, 8), HEX);
   Serial.println(adler32((uint8_t *) str4, 9), HEX);
+  Serial.println();
 }
 
 
diff --git a/libraries/Adler/keywords.txt b/libraries/Adler/keywords.txt
index 1d4ac5b4..80a5ccf2 100644
--- a/libraries/Adler/keywords.txt
+++ b/libraries/Adler/keywords.txt
@@ -2,10 +2,12 @@
 
 # Data types (KEYWORD1)
 Adler32	KEYWORD1
+Adler16	KEYWORD1
 
 
 # Methods and Functions (KEYWORD2)
 adler32	KEYWORD2
+adler16	KEYWORD2
 begin	KEYWORD2
 add	KEYWORD2
 addFast	KEYWORD2
@@ -15,5 +17,7 @@ count	KEYWORD2
 
 # Constants (LITERAL1)
 ADLER32_LIB_VERSION	LITERAL1
+ADLER16_LIB_VERSION	LITERAL1
 ADLER32_MOD_PRIME	LITERAL1
+ADLER16_MOD_PRIME	LITERAL1
 
diff --git a/libraries/Adler/library.json b/libraries/Adler/library.json
index af39b0a8..40273c61 100644
--- a/libraries/Adler/library.json
+++ b/libraries/Adler/library.json
@@ -1,6 +1,6 @@
 {
   "name": "Adler",
-  "keywords": "Adler, checksum",
+  "keywords": "Adler32, Adler16, checksum",
   "description": "Arduino Library for calculating Adler-32 checksum.",
   "authors":
   [
@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/Adler.git"
   },
-  "version": "0.1.2",
+  "version": "0.2.0",
   "license": "MIT",
   "frameworks": "arduino",
   "platforms": "*",
diff --git a/libraries/Adler/library.properties b/libraries/Adler/library.properties
index a98e896b..878ad00e 100644
--- a/libraries/Adler/library.properties
+++ b/libraries/Adler/library.properties
@@ -1,11 +1,11 @@
 name=Adler
-version=0.1.2
+version=0.2.0
 author=Rob Tillaart <rob.tillaart@gmail.com>
 maintainer=Rob Tillaart <rob.tillaart@gmail.com>
-sentence="Arduino Library for calculating Adler-32 checksum.
-paragraph=
+sentence=Arduino Library for calculating Adler-32 and Adler-16 checksum.
+paragraph=Adler-16 is experimental.
 category=Signal Input/Output
 url=https://github.com/RobTillaart/Adler
 architectures=*
-includes=Adler.h
+includes=Adler.h,Adler16.h,Adler32.h
 depends=
diff --git a/libraries/Adler/test/unit_test_001.cpp b/libraries/Adler/test/unit_test_001.cpp
index e3d179b4..a26accc5 100644
--- a/libraries/Adler/test/unit_test_001.cpp
+++ b/libraries/Adler/test/unit_test_001.cpp
@@ -27,6 +27,7 @@
 #include "Arduino.h"
 #include "Adler.h"
 
+
 char lorem[] = "Lorem ipsum dolor sit amet, \
 consectetuer adipiscing elit. Aenean commodo ligula eget dolor. \
 Aenean massa. Cum sociis natoque penatibus et magnis dis parturient \
@@ -45,7 +46,7 @@ nisi vel augue. Curabitur ullamcorper ultricies nisi. Nam eget dui.";
 
 unittest_setup()
 {
-  fprintf(stderr, "ADLER32_LIB_VERSION: %s\n", (char *) ADLER32_LIB_VERSION);
+  fprintf(stderr, "ADLER_LIB_VERSION: %s\n", (char *) ADLER_LIB_VERSION);
 }
 
 unittest_teardown()
@@ -55,11 +56,12 @@ unittest_teardown()
 
 unittest(test_constants)
 {
+  assertEqual(ADLER16_MOD_PRIME, 251);
   assertEqual(ADLER32_MOD_PRIME, 65521);
 }
 
 
-unittest(test_adler32)
+unittest(test_adler_static)
 {
   char str1[24] = "abcde";
   char str2[24] = "abcdef";
@@ -68,32 +70,10 @@ unittest(test_adler32)
   assertEqual(96993776, adler32((uint8_t *) str1, 5));
   assertEqual(136184406, adler32((uint8_t *) str2, 6));
   assertEqual(234881829, adler32((uint8_t *) str3, 8));
-}
-
-
-unittest(test_lorem)
-{
-  Adler32 ad32;
-
-  ad32.begin();
- 
-  fprintf(stderr, "strlen lorem\n");
-  assertEqual(868, strlen(lorem));
-
-  for (int i = 0; lorem[i] != 0; i++)
-  {
-    ad32.add(lorem[i]);
-  }
-  assertEqual(3972480156, ad32.getAdler());
-
-  ad32.begin();
-  ad32.add(lorem, strlen(lorem));
-  assertEqual(3972480156, ad32.getAdler());
-
-  ad32.begin();
-  ad32.addFast(lorem, strlen(lorem));
-  assertEqual(3972480156, ad32.getAdler());
 
+  assertEqual(57845, adler16((uint8_t *) str1, 5));
+  assertEqual(18016, adler16((uint8_t *) str2, 6));
+  assertEqual(17972, adler16((uint8_t *) str3, 8));
 }
 
 
diff --git a/libraries/Adler/test/unit_test_Adler16.cpp b/libraries/Adler/test/unit_test_Adler16.cpp
new file mode 100644
index 00000000..316f33f9
--- /dev/null
+++ b/libraries/Adler/test/unit_test_Adler16.cpp
@@ -0,0 +1,90 @@
+//
+//    FILE: unit_test_001.cpp
+//  AUTHOR: Rob Tillaart
+//    DATE: 2022-01-25
+// PURPOSE: unit tests for the Adler library
+//          https://github.com/RobTillaart/Adler
+//          https://github.com/Arduino-CI/arduino_ci/blob/master/REFERENCE.md
+//
+
+// supported assertions
+// https://github.com/Arduino-CI/arduino_ci/blob/master/cpp/unittest/Assertion.h#L33-L42
+// ----------------------------
+// assertEqual(expected, actual)
+// assertNotEqual(expected, actual)
+// assertLess(expected, actual)
+// assertMore(expected, actual)
+// assertLessOrEqual(expected, actual)
+// assertMoreOrEqual(expected, actual)
+// assertTrue(actual)
+// assertFalse(actual)
+// assertNull(actual)
+// assertNotNull(actual)
+
+#include <ArduinoUnitTests.h>
+
+
+#include "Arduino.h"
+#include "Adler16.h"
+
+
+char lorem[] = "Lorem ipsum dolor sit amet, \
+consectetuer adipiscing elit. Aenean commodo ligula eget dolor. \
+Aenean massa. Cum sociis natoque penatibus et magnis dis parturient \
+montes, nascetur ridiculus mus. Donec quam felis, ultricies nec, \
+pellentesque eu, pretium quis, sem. Nulla consequat massa quis enim. \
+Donec pede justo, fringilla vel, aliquet nec, vulputate eget, arcu. \
+In enim justo, rhoncus ut, imperdiet a, venenatis vitae, justo. \
+Nullam dictum felis eu pede mollis pretium. Integer tincidunt. \
+Cras dapibus. Vivamus elementum semper nisi. \
+Aenean vulputate eleifend tellus. Aenean leo ligula, porttitor eu, \
+consequat vitae, eleifend ac, enim. Aliquam lorem ante, dapibus in, \
+viverra quis, feugiat a, tellus. Phasellus viverra nulla ut metus \
+varius laoreet. Quisque rutrum. Aenean imperdiet. Etiam ultricies \
+nisi vel augue. Curabitur ullamcorper ultricies nisi. Nam eget dui.";
+
+
+unittest_setup()
+{
+  fprintf(stderr, "ADLER16_LIB_VERSION: %s\n", (char *) ADLER16_LIB_VERSION);
+}
+
+unittest_teardown()
+{
+}
+
+
+unittest(test_constants)
+{
+  assertEqual(ADLER16_MOD_PRIME, 251);
+}
+
+
+unittest(test_ADLER16_lorem)
+{
+  Adler16 ad16;
+
+  ad16.begin();
+ 
+  fprintf(stderr, "strlen lorem\n");
+  assertEqual(868, strlen(lorem));
+
+  for (int i = 0; lorem[i] != 0; i++)
+  {
+    ad16.add(lorem[i]);
+  }
+  assertEqual(57303, ad16.getAdler());
+
+  ad16.begin();
+  ad16.add(lorem, strlen(lorem));
+  assertEqual(57303, ad16.getAdler());
+
+  ad16.begin();
+  ad16.addFast(lorem, strlen(lorem));
+  assertEqual(57303, ad16.getAdler());
+}
+
+
+unittest_main()
+
+// --------
diff --git a/libraries/Adler/test/unit_test_Adler32.cpp b/libraries/Adler/test/unit_test_Adler32.cpp
new file mode 100644
index 00000000..0868c096
--- /dev/null
+++ b/libraries/Adler/test/unit_test_Adler32.cpp
@@ -0,0 +1,91 @@
+//
+//    FILE: unit_test_001.cpp
+//  AUTHOR: Rob Tillaart
+//    DATE: 2022-01-25
+// PURPOSE: unit tests for the Adler library
+//          https://github.com/RobTillaart/Adler
+//          https://github.com/Arduino-CI/arduino_ci/blob/master/REFERENCE.md
+//
+
+// supported assertions
+// https://github.com/Arduino-CI/arduino_ci/blob/master/cpp/unittest/Assertion.h#L33-L42
+// ----------------------------
+// assertEqual(expected, actual)
+// assertNotEqual(expected, actual)
+// assertLess(expected, actual)
+// assertMore(expected, actual)
+// assertLessOrEqual(expected, actual)
+// assertMoreOrEqual(expected, actual)
+// assertTrue(actual)
+// assertFalse(actual)
+// assertNull(actual)
+// assertNotNull(actual)
+
+#include <ArduinoUnitTests.h>
+
+
+#include "Arduino.h"
+#include "Adler32.h"
+
+
+char lorem[] = "Lorem ipsum dolor sit amet, \
+consectetuer adipiscing elit. Aenean commodo ligula eget dolor. \
+Aenean massa. Cum sociis natoque penatibus et magnis dis parturient \
+montes, nascetur ridiculus mus. Donec quam felis, ultricies nec, \
+pellentesque eu, pretium quis, sem. Nulla consequat massa quis enim. \
+Donec pede justo, fringilla vel, aliquet nec, vulputate eget, arcu. \
+In enim justo, rhoncus ut, imperdiet a, venenatis vitae, justo. \
+Nullam dictum felis eu pede mollis pretium. Integer tincidunt. \
+Cras dapibus. Vivamus elementum semper nisi. \
+Aenean vulputate eleifend tellus. Aenean leo ligula, porttitor eu, \
+consequat vitae, eleifend ac, enim. Aliquam lorem ante, dapibus in, \
+viverra quis, feugiat a, tellus. Phasellus viverra nulla ut metus \
+varius laoreet. Quisque rutrum. Aenean imperdiet. Etiam ultricies \
+nisi vel augue. Curabitur ullamcorper ultricies nisi. Nam eget dui.";
+
+
+unittest_setup()
+{
+  fprintf(stderr, "ADLER32_LIB_VERSION: %s\n", (char *) ADLER32_LIB_VERSION);
+}
+
+unittest_teardown()
+{
+}
+
+
+unittest(test_constants)
+{
+  assertEqual(ADLER32_MOD_PRIME, 65521);
+}
+
+
+unittest(test_ADLER32_lorem)
+{
+  Adler32 ad32;
+
+  ad32.begin();
+ 
+  fprintf(stderr, "strlen lorem\n");
+  assertEqual(868, strlen(lorem));
+
+  for (int i = 0; lorem[i] != 0; i++)
+  {
+    ad32.add(lorem[i]);
+  }
+  assertEqual(3972480156, ad32.getAdler());
+
+  ad32.begin();
+  ad32.add(lorem, strlen(lorem));
+  assertEqual(3972480156, ad32.getAdler());
+
+  ad32.begin();
+  ad32.addFast(lorem, strlen(lorem));
+  assertEqual(3972480156, ad32.getAdler());
+
+}
+
+
+unittest_main()
+
+// --------