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Corrected the encoding and decoding of the bit string.

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This commit is contained in:
skarg
2005-04-15 15:30:21 +00:00
parent 347c5b4607
commit a58d07406a
2 changed files with 46 additions and 20 deletions
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bacnet-stack/bacdcode.c
+46 -20
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@@ -553,14 +553,16 @@ int decode_bitstring(uint8_t * apdu, uint32_t len_value,
uint8_t unused_bits = 0;
uint32_t i = 0;
uint32_t bytes_used = 0;
bitstring_init(bit_string);
if (len_value && ((len_value - 1) < MAX_BITSTRING_BYTES))
if (len_value)
{
// the first octet contains the unused bits
bytes_used = len_value--;
len = 1;
// the first octet contains the unused bits
bytes_used = len_value - 1;
if (bytes_used <= MAX_BITSTRING_BYTES)
{
len = 1;
for (i = 0; i < bytes_used; i++)
{
bit_string->value[i] = apdu[len++];
@@ -568,32 +570,53 @@ int decode_bitstring(uint8_t * apdu, uint32_t len_value,
unused_bits = apdu[0] & 0x07;
bit_string->bits_used = bytes_used * 8;
bit_string->bits_used -= unused_bits;
}
}
return len;
}
// returns the number of bytes that a bit string is using
static int bitstring_bytes_used(BACNET_BIT_STRING *bit_string)
{
int len = 0; // return value
uint8_t used_bytes = 0;
uint8_t last_bit = 0;
if (bit_string->bits_used)
{
last_bit = bit_string->bits_used - 1;
used_bytes = last_bit / 8;
// add one for the first byte
used_bytes++;
len = used_bytes;
}
return len;
}
// from clause 20.2.10 Encoding of a Bit String Value
// returns the number of apdu bytes consumed
int encode_bitstring(uint8_t * apdu, BACNET_BIT_STRING *bit_string)
{
int len = 0;
uint8_t used_bits = 0;
uint8_t remaining_used_bits = 0;
uint8_t used_bytes = 0;
uint8_t i = 0;
uint8_t i = 0;
// possible to encode an empty bit string
if (bit_string->bits_used)
used_bytes = (bit_string->bits_used / 8) + 1;
used_bits = bit_string->bits_used - (used_bytes * 8);
// if the bit string is empty, then the first octet shall be zero
if (bit_string->bits_used)
apdu[len++] = 8 - used_bits;
else
if (bit_string->bits_used == 0)
apdu[len++] = 0;
for (i = 0; i < used_bytes; i++)
else
{
apdu[len++] = bit_string->value[i];
used_bytes = bitstring_bytes_used(bit_string);
remaining_used_bits = bit_string->bits_used - ((used_bytes - 1) * 8);
// number of unused bits in the subsequent final octet
apdu[len++] = 8 - remaining_used_bits;
for (i = 0; i < used_bytes; i++)
{
apdu[len++] = bit_string->value[i];
}
}
return len;
@@ -602,10 +625,13 @@ int encode_bitstring(uint8_t * apdu, BACNET_BIT_STRING *bit_string)
int encode_tagged_bitstring(uint8_t * apdu, BACNET_BIT_STRING *bit_string)
{
int len = 0;
int bit_string_encoded_length = 1;// 1 for the bits remaining octet
// assumes that the tag only consumes 1 octet
len = encode_bitstring(&apdu[1], bit_string);
len += encode_tag(&apdu[0], BACNET_APPLICATION_TAG_BIT_STRING, false, len);
// bit string may use more than 1 octet for the tag, so find out how many
bit_string_encoded_length += bitstring_bytes_used(bit_string);
len = encode_tag(&apdu[0], BACNET_APPLICATION_TAG_BIT_STRING, false,
bit_string_encoded_length);
len += encode_bitstring(&apdu[len], bit_string);
return len;
}