refactor:c++ implementation

imnemo · Aug 7, 2017 · c65f543 · c65f543
1 parent 7f3e383
commit c65f543
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Showing 2 changed files with 45 additions and 26 deletions.
diff --git a/lib/crc16.cc b/lib/crc16.cc
@@ -65,28 +65,37 @@ static uint8_t const CRCLowTbl[256] = {
     0x43, 0x83, 0x41, 0x81, 0x80, 0x40};
 
 /**
-* check crc16 sum by table look-up
-* @param [point] *pDataIn data to be checked
-* @param [int] len data length
-* @return [char*] result sum, hex code string
-**/
-char *CRC16CheckSum(uint8_t *pDataIn, int len)
+ * place where magic truely works
+ **/
+void checkSum(uint8_t *pDataIn, int len, uint8_t *sumHigh, uint8_t *sumLow)
 {
     uint8_t tableIndex = 0;
-    uint8_t sumHigh = 0xFF;
-    uint8_t sumLow = 0xFF;
 
+    //采用len控制for循环结束，更灵活
+    //这样可以对input的一部分做计算
     int i = 0;
     if ((0 != len) && (NULL != pDataIn))
     {
         for (i = len; i > 0; i--)
         {
-            tableIndex = sumHigh ^ (*pDataIn++);
-            sumHigh = sumLow ^ CRCHighTbl[tableIndex];
-            sumLow = CRCLowTbl[tableIndex];
+            tableIndex = *sumHigh ^ (*pDataIn++);
+            *sumHigh = *sumLow ^ CRCHighTbl[tableIndex];
+            *sumLow = CRCLowTbl[tableIndex];
         }
     }
+}
 
+/**
+* check crc16 sum by table look-up
+* @param [point] *pDataIn data to be checked
+* @param [int] len data length
+* @return [char*] result sum, hex code string
+**/
+char *CRC16CheckSum(uint8_t *pDataIn, int len)
+{
+    uint8_t sumHigh = 0xFF;
+    uint8_t sumLow = 0xFF;
+    checkSum(pDataIn, len, &sumHigh, &sumLow);
     char *sum = new char[5];
     sprintf(sum, "%02x%02x", sumHigh, sumLow);
     return sum;
@@ -96,29 +105,33 @@ char *CRC16CheckSum(uint8_t *pDataIn, int len)
 * check crc16 sum by table look-up
 * @param [unsigned char*] *pDataIn data to be checked
 * @param [int] len data length
-* @param [unsigned char*] sum result variable, blow edged
+* @param [unsigned char* array] sum result, BigEndian
 * @return void
 **/
 void CRC16CheckSum(uint8_t *pDataIn, int len, uint8_t *sum)
 {
-    uint8_t tableIndex = 0;
     uint8_t sumHigh = 0xFF;
     uint8_t sumLow = 0xFF;
-
-    int i = 0;
-    if ((0 != len) && (NULL != pDataIn))
-    {
-        for (i = len; i > 0; i--)
-        {
-            tableIndex = sumHigh ^ (*pDataIn++);
-            sumHigh = sumLow ^ CRCHighTbl[tableIndex];
-            sumLow = CRCLowTbl[tableIndex];
-        }
-    }
+    checkSum(pDataIn, len, &sumHigh, &sumLow);
     *sum++ = sumHigh;
     *sum = sumLow;
 }
 
+/**
+* check crc16 sum by table look-up
+* @param [unsigned char*] *pDataIn data to be checked
+* @param [int] len data length
+* @param [unsigned short* number] sum result
+* @return void
+**/
+void CRC16CheckSum(uint8_t *pDataIn, int len, uint16_t *sum)
+{
+    uint8_t sumHigh = 0xFF;
+    uint8_t sumLow = 0xFF;
+    checkSum(pDataIn, len, &sumHigh, &sumLow);
+    *sum = (sumHigh << 8 | sumLow);
+}
+
 /**
 * verify crc16 sum by table look-up
 * @param [unsigned char*] *pDataIn data to be checked
@@ -131,16 +144,15 @@ bool CRC16VerifySum(uint8_t *pDataIn, int len)
     uint8_t sumHigh = 0xFF;
     uint8_t sumLow = 0xFF;
 
-    int i = 0;
     if ((0 == len) || (NULL == pDataIn))
     {
         return false;
     }
 
+    int i = 0;
     for (i = len; i > 0; i--)
     {
         tableIndex = sumHigh ^ (*pDataIn++);
-
         sumHigh = sumLow ^ CRCHighTbl[tableIndex];
         sumLow = CRCLowTbl[tableIndex];
     }

diff --git a/test_cpp/crc16_test.cc b/test_cpp/crc16_test.cc
@@ -26,6 +26,13 @@ TEST_CASE("CRC16 sum are computed")
         REQUIRE(sum == "96ce");
     }
 
+    SECTION("Checksum can return an unsigned short number")
+    {
+        uint16_t sum;
+        CRC16CheckSum(stream, 24, &sum);
+        REQUIRE(sum == 38606);
+    }
+
     SECTION("Verifysum should be passed")
     {
         bool isValid = CRC16VerifySum(stream, 26);