From 8a9a690a2a33d0292ec5d490d867c1153a8bef44 Mon Sep 17 00:00:00 2001
From: walchko <walchko@users.noreply.github.com>
Date: Wed, 22 Nov 2023 14:55:05 -0700
Subject: [PATCH] update

---
 cpp/examples/crc.cpp | 67 ++++++++++++++++++++++++++++++++++++++++++++
 cpp/src/crc.hpp      | 40 ++++++++++++++++++++++++++
 cpp/src/yivopack.hpp | 16 +++++++++++
 readme.md            |  3 ++
 4 files changed, 126 insertions(+)
 create mode 100644 cpp/examples/crc.cpp
 create mode 100644 cpp/src/crc.hpp

diff --git a/cpp/examples/crc.cpp b/cpp/examples/crc.cpp
new file mode 100644
index 0000000..6641907
--- /dev/null
+++ b/cpp/examples/crc.cpp
@@ -0,0 +1,67 @@
+#include <stdio.h>
+#include <stdint.h>
+
+#define CRC8_POLYNOMIAL 0x07
+
+// Function to generate CRC-8 lookup table
+void generate8(uint8_t table[256]) {
+    for (uint16_t i = 0; i < 256; ++i) {
+        uint8_t crc = i;
+        for (size_t j = 1; j < 8; j++) {
+            crc = (crc & 0x80) ? (crc << 1) ^ CRC8_POLYNOMIAL : crc << 1;
+        }
+        table[i] = crc;
+    }
+}
+
+#define CRC16_POLYNOMIAL 0x8005
+
+// Function to generate CRC-16 lookup table
+void generate16(uint16_t table[256]) {
+    for (uint16_t i = 0; i < 256; ++i) {
+        uint16_t crc = i;
+        for (int j = 0; j < 8; ++j) {
+            crc = (crc & 1) ? (crc >> 1) ^ CRC16_POLYNOMIAL : (crc >> 1);
+        }
+        table[i] = crc;
+    }
+}
+
+int main() {
+    // Example data
+    // uint8_t data[] = "Hello, CRC!";
+    uint16_t table[256];
+    uint8_t table8[256];
+
+    generate8(table8);
+
+    // Print the result
+    for (size_t i=0; i<16; ++i) {
+        for (size_t j=0; j<16; ++j) {
+            // printf("0x%02X,", table8[i*16+j]);
+            printf("%u,", table8[i*16+j]);
+        }
+        printf("\n");
+    }
+
+    printf("--------------------------\n");
+
+    generate16(table);
+
+    // Print the result
+    for (size_t i=0; i<16; ++i) {
+        for (size_t j=0; j<16; ++j) {
+            printf("0x%04X,", table[i*16+j]);
+        }
+        printf("\n");
+    }
+
+    /*
+    crc = 0
+    for byte in message:
+      crcByte = byte^crc
+      crc = table[crcByte]
+    */
+
+    return 0;
+}
\ No newline at end of file
diff --git a/cpp/src/crc.hpp b/cpp/src/crc.hpp
new file mode 100644
index 0000000..b0f21ec
--- /dev/null
+++ b/cpp/src/crc.hpp
@@ -0,0 +1,40 @@
+
+#pragma once
+
+#include <cstdint>
+
+// // CRC-8 polynomial (0x07)
+// #define CRC8_POLYNOMIAL 0x07
+
+// // Function to calculate CRC-8 checksum
+// uint8_t crc8(const uint8_t *data, size_t length) {
+//     uint8_t crc = 0;
+
+//     for (size_t i = 0; i < length; ++i) {
+//         crc ^= data[i];
+
+//         for (int j = 0; j < 8; ++j) {
+//             crc = (crc & 0x80) ? (crc << 1) ^ CRC8_POLYNOMIAL : (crc << 1);
+//         }
+//     }
+
+//     return crc;
+// }
+
+// // CRC-16 polynomial (0x8005)
+// #define CRC16_POLYNOMIAL 0x8005
+
+// // Function to calculate CRC-16 checksum
+// uint16_t crc16(const uint8_t *data, size_t length) {
+//     uint16_t crc = 0xFFFF;
+
+//     for (size_t i = 0; i < length; ++i) {
+//         crc ^= (uint16_t)data[i];
+
+//         for (int j = 0; j < 8; ++j) {
+//             crc = (crc & 0x0001) ? (crc >> 1) ^ CRC16_POLYNOMIAL : (crc >> 1);
+//         }
+//     }
+
+//     return crc;
+// }
\ No newline at end of file
diff --git a/cpp/src/yivopack.hpp b/cpp/src/yivopack.hpp
index 85a47f4..3c60d66 100644
--- a/cpp/src/yivopack.hpp
+++ b/cpp/src/yivopack.hpp
@@ -39,9 +39,25 @@ class YivoPack_t: public std::vector<uint8_t> {
   uint8_t msgid() { return (*this)[4]; }
   uint16_t playload_size() { return ((*this)[3] << 8) | (*this)[2];}
   uint8_t checksum() { return (*this)[size()-1]; }
+  void set_checksum() { (*this)[size()-1]; }
   // uint16_t playload_size() { return size() - 6;}
+  uint8_t calc_checksum() {
+    uint8_t cs = 0;
+    uint16_t payload_size = this->payload_size();
+    uint8_t *data = this->data();
+    for (uint16_t i = 0; i < payload_size; ++i) {
+      cs ^= data[2+i];
+    }
+    return cs;
+  }
+  bool has_valide_chksum() {
+    return this->calc_checksum() == this->checksum();
+  }
 };
 
+typedef YivoPack_t ypkt_t; // rename to this?
+
+
 namespace yivo {
 static
 std::string to_string(const YivoPack_t& msg) {
diff --git a/readme.md b/readme.md
index e6170cc..86bb562 100644
--- a/readme.md
+++ b/readme.md
@@ -30,6 +30,9 @@ Trying to standardize the way I access sensors.
       not dependant on the message format other than, it is a `struct`
 - [x] Make a header only library
 - [ ] Generate C and Python messages from a template instead of writing independently
+- [ ] rename `YivoPack_t` to something else like `ypkt_t`
+    - [ ] Add method `bool has_valid_chksum()`? Class could calculate checksum and then compare
+    to its checksum
 
 ## Python