BootloaderTest: Refactor CRC calculation

This introduces a Crc helper class to make it easier to mix single bytes
and buffers in a CRC calculation. It should not change any behaviour
yet.

Author: matthijskooijman

BootloaderTest/BootloaderTest.ino

@@ -70,7 +70,7 @@ bool write_command(uint8_t cmd, uint8_t *dataout, uint8_t len, uint8_t crc_xor =
   for (uint8_t i = 0; i < len; ++i)
     assertAck(bus.write(dataout[i]));
 
-  uint8_t crc = calcCrc(cmd, dataout, len);
+  uint8_t crc = Crc().update(cmd).update(dataout, len).get();
   assertAck(bus.write(crc ^ crc_xor));
 
   if (!cfg.repStartAfterWrite)
@@ -105,7 +105,8 @@ bool read_status(uint8_t *status, uint8_t *datain, uint8_t okLen, uint8_t failLe
   else
     assertAck(bus.readThenNack(crc));
 
-  assertEqual(crc, calcCrc(*status, datain, expectedLen));
+  uint8_t expectedCrc = Crc().update(*status).update(datain, expectedLen).get();
+  assertEqual(crc, expectedCrc);
   if (!cfg.repStartAfterRead)
     bus.stop();
   return true;

BootloaderTest/Util.h

@@ -38,9 +38,30 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #define assertAck(result) assertEqual(result, SoftWire::ack)
 #define assertOk(status) assertEqual(status, Status::COMMAND_OK)
 
-inline uint8_t calcCrc(uint8_t first, uint8_t *rest, uint8_t len) {
-        uint8_t crc = _crc8_ccitt_update(0xff, first);
-        for (uint8_t i = 0; i < len; ++i)
-          crc = _crc8_ccitt_update(crc, rest[i]);
-        return crc;
-}
+/**
+ * Helper class to calculate crcs for transfers. To use it, create an
+ * instance, call update() for each byte and/or buffer of bytes to
+ * calculate the CRC over, and then call get() to get the result.
+ * update() is chainable, so you can do e.g.:
+ *
+ *   uint8_t crc = Crc().update(first_byte).update(rest_of_bytes, len).get();
+ */
+class Crc {
+  public:
+    Crc& update(uint8_t b) {
+      this->crc = _crc8_ccitt_update(this->crc, b);
+      return *this;
+    }
+
+    Crc& update(uint8_t *buf, uint8_t len) {
+      for (uint8_t i = 0; i < len; ++i)
+        this->update(buf[i]);
+      return *this;
+    }
+    uint8_t get() {
+      return this->crc;
+    }
+
+  private:
+    uint8_t crc = 0xff;
+};