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tidy up read_value() function

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proddy
2020-09-04 12:31:52 +02:00
parent e76bdd76b1
commit 142480cecc
1 changed files with 9 additions and 9 deletions
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18
src/telegram.h
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@@ -92,27 +92,27 @@ class Telegram {
value = (uint8_t)(((message_data[abs_index]) >> (bit)) & 0x01);
}
// read values from a telegram. We always store the value, regardless if its garbage
// read a value from a telegram. We always store the value, regardless if its garbage
template <typename Value>
// assuming negative numbers are stored as 2's-complement
// https://medium.com/@LeeJulija/how-integers-are-stored-in-memory-using-twos-complement-5ba04d61a56c
// 2-compliment : https://www.rapidtables.com/convert/number/decimal-to-hex.html
// https://en.wikipedia.org/wiki/Two%27s_complement
// s is to override number of bytes read (e.g. use 3 to simulat a uint24_t)
// s is to override number of bytes read (e.g. use 3 to simulate a uint24_t)
void read_value(Value & value, const uint8_t index, uint8_t s = 0) const {
uint8_t size = (!s) ? sizeof(Value) : s;
int8_t abs_index = ((index - offset + size - 1) >= message_length) ? -1 : (index - offset);
if (abs_index < 0) {
return; // out of bounds, we don't change the value
uint8_t num_bytes = (!s) ? sizeof(Value) : s;
// check for out of bounds, if so don't modify the value
if ((index - this->offset + num_bytes - 1) >= this->message_length) {
return;
}
value = 0;
for (uint8_t i = 0; i < size; i++) {
value = (value << 8) + message_data[abs_index + i]; // shift
for (uint8_t i = 0; i < num_bytes; i++) {
value = (value << 8) + message_data[index - this->offset + i]; // shift by byte
}
}
private:
int8_t _getDataPosition(const uint8_t index, const uint8_t size) const;
};