From 4b6301d4ce91638d39689f7be7db797f99623964 Mon Sep 17 00:00:00 2001
From: rtang09 <49603415+rtang09@users.noreply.github.com>
Date: Wed, 4 Oct 2023 23:12:08 -0700
Subject: [PATCH] Fletcher 16 (#9775)

* Add files via upload

* Update fletcher16.py

* Update fletcher16.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update fletcher16.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update fletcher16.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update fletcher16.py

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>
---
 hashes/fletcher16.py | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 hashes/fletcher16.py

diff --git a/hashes/fletcher16.py b/hashes/fletcher16.py
new file mode 100644
index 000000000..7c23c98d7
--- /dev/null
+++ b/hashes/fletcher16.py
@@ -0,0 +1,36 @@
+"""
+The Fletcher checksum is an algorithm for computing a position-dependent
+checksum devised by John G. Fletcher (1934–2012) at Lawrence Livermore Labs
+in the late 1970s.[1] The objective of the Fletcher checksum was to
+provide error-detection properties approaching those of a cyclic
+redundancy check but with the lower computational effort associated
+with summation techniques.
+
+Source: https://en.wikipedia.org/wiki/Fletcher%27s_checksum
+"""
+
+
+def fletcher16(text: str) -> int:
+    """
+    Loop through every character in the data and add to two sums.
+
+    >>> fletcher16('hello world')
+    6752
+    >>> fletcher16('onethousandfourhundredthirtyfour')
+    28347
+    >>> fletcher16('The quick brown fox jumps over the lazy dog.')
+    5655
+    """
+    data = bytes(text, "ascii")
+    sum1 = 0
+    sum2 = 0
+    for character in data:
+        sum1 = (sum1 + character) % 255
+        sum2 = (sum1 + sum2) % 255
+    return (sum2 << 8) | sum1
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()