From 5b134d7e9ec2b7cd036c8a2f4e52ddc39a6135d7 Mon Sep 17 00:00:00 2001
From: MikeCAT <mikecat@users.noreply.github.com>
Date: Wed, 2 Nov 2022 21:54:45 +0900
Subject: [PATCH] fix Fletcher-32/64 Checksum

* Operate on words, not bytes
* Add tests
---
 src/core/operations/Fletcher32Checksum.mjs   |  14 ++-
 src/core/operations/Fletcher64Checksum.mjs   |  18 +++-
 tests/operations/index.mjs                   |   1 +
 tests/operations/tests/FletcherChecksum.mjs  | 108 +++++++++++++++++++
 tests/operations/tests/GenerateAllHashes.mjs |   4 +-
 5 files changed, 137 insertions(+), 8 deletions(-)
 create mode 100644 tests/operations/tests/FletcherChecksum.mjs

diff --git a/src/core/operations/Fletcher32Checksum.mjs b/src/core/operations/Fletcher32Checksum.mjs
index 29c74535..7b41ce55 100644
--- a/src/core/operations/Fletcher32Checksum.mjs
+++ b/src/core/operations/Fletcher32Checksum.mjs
@@ -35,10 +35,18 @@ class Fletcher32Checksum extends Operation {
     run(input, args) {
         let a = 0,
             b = 0;
-        input = new Uint8Array(input);
+        if (ArrayBuffer.isView(input)) {
+            input = new DataView(input.buffer, input.byteOffset, input.byteLength);
+        } else {
+            input = new DataView(input);
+        }
 
-        for (let i = 0; i < input.length; i++) {
-            a = (a + input[i]) % 0xffff;
+        for (let i = 0; i < input.byteLength - 1; i += 2) {
+            a = (a + input.getUint16(i, true)) % 0xffff;
+            b = (b + a) % 0xffff;
+        }
+        if (input.byteLength % 2 !== 0) {
+            a = (a + input.getUint8(input.byteLength - 1)) % 0xffff;
             b = (b + a) % 0xffff;
         }
 
diff --git a/src/core/operations/Fletcher64Checksum.mjs b/src/core/operations/Fletcher64Checksum.mjs
index 1d0d5bd9..68328ea3 100644
--- a/src/core/operations/Fletcher64Checksum.mjs
+++ b/src/core/operations/Fletcher64Checksum.mjs
@@ -35,10 +35,22 @@ class Fletcher64Checksum extends Operation {
     run(input, args) {
         let a = 0,
             b = 0;
-        input = new Uint8Array(input);
+        if (ArrayBuffer.isView(input)) {
+            input = new DataView(input.buffer, input.byteOffset, input.byteLength);
+        } else {
+            input = new DataView(input);
+        }
 
-        for (let i = 0; i < input.length; i++) {
-            a = (a + input[i]) % 0xffffffff;
+        for (let i = 0; i < input.byteLength - 3; i += 4) {
+            a = (a + input.getUint32(i, true)) % 0xffffffff;
+            b = (b + a) % 0xffffffff;
+        }
+        if (input.byteLength % 4 !== 0) {
+            let lastValue = 0;
+            for (let i = 0; i < input.byteLength % 4; i++) {
+                lastValue = (lastValue << 8) | input.getUint8(input.byteLength - 1 - i);
+            }
+            a = (a + lastValue) % 0xffffffff;
             b = (b + a) % 0xffffffff;
         }
 
diff --git a/tests/operations/index.mjs b/tests/operations/index.mjs
index 19e70970..fe1c4e00 100644
--- a/tests/operations/index.mjs
+++ b/tests/operations/index.mjs
@@ -124,6 +124,7 @@ import "./tests/UnescapeString.mjs";
 import "./tests/LS47.mjs";
 import "./tests/LZString.mjs";
 import "./tests/NTLM.mjs";
+import "./tests/FletcherChecksum.mjs";
 
 // Cannot test operations that use the File type yet
 // import "./tests/SplitColourChannels.mjs";
diff --git a/tests/operations/tests/FletcherChecksum.mjs b/tests/operations/tests/FletcherChecksum.mjs
new file mode 100644
index 00000000..de23abdc
--- /dev/null
+++ b/tests/operations/tests/FletcherChecksum.mjs
@@ -0,0 +1,108 @@
+/**
+ * @author mikecat
+ * @copyright Crown Copyright 2022
+ * @license Apache-2.0
+ */
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "Fletcher-16 Checksum: abcde",
+        input: "abcde",
+        expectedOutput: "c8f0",
+        recipeConfig: [
+            {
+                op: "Fletcher-16 Checksum",
+                args: [],
+            },
+        ],
+    },
+    {
+        name: "Fletcher-16 Checksum: abcdef",
+        input: "abcdef",
+        expectedOutput: "2057",
+        recipeConfig: [
+            {
+                op: "Fletcher-16 Checksum",
+                args: [],
+            },
+        ],
+    },
+    {
+        name: "Fletcher-16 Checksum: abcdefgh",
+        input: "abcdefgh",
+        expectedOutput: "0627",
+        recipeConfig: [
+            {
+                op: "Fletcher-16 Checksum",
+                args: [],
+            },
+        ],
+    },
+    {
+        name: "Fletcher-32 Checksum: abcde",
+        input: "abcde",
+        expectedOutput: "f04fc729",
+        recipeConfig: [
+            {
+                op: "Fletcher-32 Checksum",
+                args: [],
+            },
+        ],
+    },
+    {
+        name: "Fletcher-32 Checksum: abcdef",
+        input: "abcdef",
+        expectedOutput: "56502d2a",
+        recipeConfig: [
+            {
+                op: "Fletcher-32 Checksum",
+                args: [],
+            },
+        ],
+    },
+    {
+        name: "Fletcher-32 Checksum: abcdefgh",
+        input: "abcdefgh",
+        expectedOutput: "ebe19591",
+        recipeConfig: [
+            {
+                op: "Fletcher-32 Checksum",
+                args: [],
+            },
+        ],
+    },
+    {
+        name: "Fletcher-64 Checksum: abcde",
+        input: "abcde",
+        expectedOutput: "c8c6c527646362c6",
+        recipeConfig: [
+            {
+                op: "Fletcher-64 Checksum",
+                args: [],
+            },
+        ],
+    },
+    {
+        name: "Fletcher-64 Checksum: abcdef",
+        input: "abcdef",
+        expectedOutput: "c8c72b276463c8c6",
+        recipeConfig: [
+            {
+                op: "Fletcher-64 Checksum",
+                args: [],
+            },
+        ],
+    },
+    {
+        name: "Fletcher-64 Checksum: abcdefgh",
+        input: "abcdefgh",
+        expectedOutput: "312e2b28cccac8c6",
+        recipeConfig: [
+            {
+                op: "Fletcher-64 Checksum",
+                args: [],
+            },
+        ],
+    },
+]);
diff --git a/tests/operations/tests/GenerateAllHashes.mjs b/tests/operations/tests/GenerateAllHashes.mjs
index 28707bde..8e4a849a 100644
--- a/tests/operations/tests/GenerateAllHashes.mjs
+++ b/tests/operations/tests/GenerateAllHashes.mjs
@@ -58,8 +58,8 @@ CTPH:         A:E:E
 Checksums:
 Fletcher-8:   3d
 Fletcher-16:  5dc1
-Fletcher-32:  045901c0
-Fletcher-64:  00000459000001c0
+Fletcher-32:  3f5cd9e7
+Fletcher-64:  7473657474736574
 Adler-32:     045d01c1
 CRC-8:        b9
 CRC-16:       f82e