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Represent big integers as arrays of bytes #87

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Represent big integers as arrays of bytes #87

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45775f8
fix minor style issues
barsnick Oct 21, 2024
235b878
comment on size decision
barsnick Oct 21, 2024
89f70bc
signed decoder: convert EXI raw 7 bit integer octet array to 8 bit oc…
barsnick Oct 21, 2024
9b4171d
signed encoder: convert 8 bit octet array to EXI raw 7 bit integer oc…
barsnick Oct 21, 2024
cc31c50
fix minor style issues
barsnick Oct 24, 2024
57bdd1a
avoid adding zero bytes/octets at the ends of the sequences
barsnick Oct 24, 2024
f5e6d0d
drop dead code
barsnick Oct 24, 2024
9525138
implement array reversal function
barsnick Oct 24, 2024
98e3fd3
reverse the byte orders of the raw large integer byte arrays
barsnick Oct 24, 2024
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49 changes: 33 additions & 16 deletions src/input/code_templates/c/static_code/exi_basetypes.c.jinja
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,7 @@ int exi_basetypes_convert_to_unsigned(exi_unsigned_t* exi_unsigned, uint32_t val
exi_unsigned->octets_count++;
*current_octet = (uint8_t)(dummy & EXI_BASETYPES_OCTET_SEQ_VALUE_MASK);

dummy = dummy >> 7u;
dummy >>= 7u;
if (dummy == 0)
{
break;
Expand All @@ -45,7 +45,7 @@ int exi_basetypes_convert_64_to_unsigned(exi_unsigned_t* exi_unsigned, uint64_t
exi_unsigned->octets_count++;
*current_octet = (uint8_t)(dummy & EXI_BASETYPES_OCTET_SEQ_VALUE_MASK);

dummy = dummy >> 7u;
dummy >>= 7u;
if (dummy == 0)
{
break;
Expand Down Expand Up @@ -134,6 +134,24 @@ int exi_basetypes_convert_64_from_signed(const exi_signed_t* exi_signed, int64_t
return res;
}

static void _reverse_array(uint8_t* data, size_t data_size)
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@SiebrenW SiebrenW Oct 26, 2024 •
edited
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I get why we want to reverse it, but I rather see it written backwards from the get go to speed it up a bit.

Nice to have. I realise this is technically not easy.

{
if (!data || !data_size)
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If this function is static and you control the inputs, why should it have such a silent error handling of data? It will have gone wrong in exi_basetypes_convert_bytes_from_unsigned before this function is reached.

data_size makes sense of course.

{
return;
}

size_t i = 0;
size_t j = data_size - 1;
while (i < j) {
const uint8_t temp = data[i];
data[i] = data[j];
data[j] = temp;
i++;
j--;
}
}

int exi_basetypes_convert_bytes_from_unsigned(const exi_unsigned_t* exi_unsigned, uint8_t* data, size_t* data_len, size_t data_size)
{
const uint8_t* current_octet = exi_unsigned->octets;
Expand All @@ -145,21 +163,24 @@ int exi_basetypes_convert_bytes_from_unsigned(const exi_unsigned_t* exi_unsigned
temp += ((uint16_t)(*current_octet & EXI_BASETYPES_OCTET_SEQ_VALUE_MASK) << total_offset);
total_offset += 7;
if (total_offset >= 8) {
if (data_size == *data_len) {
if (*data_len >= data_size) {
return EXI_ERROR__ENCODED_INTEGER_SIZE_LARGER_THAN_DESTINATION;
}
total_offset -= 8;
data[(*data_len)++] = temp & 0xFF;
data[*data_len] = temp & 0xFF;
(*data_len)++;
temp >>= 8;
}
current_octet++;
}
if (total_offset != 0) {
if (data_size == *data_len) {
if (total_offset != 0 && (temp & 0xFF) != 0) {
if (*data_len >= data_size) {
return EXI_ERROR__ENCODED_INTEGER_SIZE_LARGER_THAN_DESTINATION;
}
data[(*data_len)++] = temp & 0xFF;
data[*data_len] = temp & 0xFF;
(*data_len)++;
}
_reverse_array(data, *data_len);
return EXI_ERROR__NO_ERROR;
}

Expand All @@ -169,24 +190,20 @@ int exi_basetypes_convert_bytes_to_unsigned(exi_unsigned_t* exi_unsigned, const
uint16_t dummy = 0;
uint8_t dummy_count = 0;

for (size_t n = 0; n != data_len; n++, current_octet++) {
for (size_t n = 0; n < data_len; n++, current_octet++) {
if (dummy_count <= 8) {
dummy |= (data[n] << dummy_count);
dummy |= (data[data_len - n - 1] << dummy_count);
dummy_count += 8;
}
exi_unsigned->octets_count++;
*current_octet = (uint8_t)(dummy & EXI_BASETYPES_OCTET_SEQ_VALUE_MASK);
*current_octet |= EXI_BASETYPES_OCTET_SEQ_FLAG_MASK;

dummy >>= 7u;
dummy_count -= 7;
if (n == data_len) {
break;
}

*current_octet |= EXI_BASETYPES_OCTET_SEQ_FLAG_MASK;
}
if (dummy_count > 0) {
*(current_octet-1) |= EXI_BASETYPES_OCTET_SEQ_FLAG_MASK;
if (dummy_count > 0 && dummy != 0) {
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@SebaLukas SebaLukas Oct 24, 2024 •
edited
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Is dummy != 0 here necessary?
It's relevant, I just read dummy_count twice...

*(current_octet - 1) |= EXI_BASETYPES_OCTET_SEQ_FLAG_MASK;
exi_unsigned->octets_count++;
*current_octet = (uint8_t)(dummy & EXI_BASETYPES_OCTET_SEQ_VALUE_MASK);
}
Expand Down
2 changes: 2 additions & 0 deletions src/input/code_templates/c/static_code/exi_basetypes.h.jinja
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,8 @@
#define EXI_STRING_MAX_LEN 64
#define EXI_BYTE_ARRAY_MAX_LEN 350

// To support EXI integer 8/7 coding, this needs to be 8/7 of the desired
// size of 25 for EXI representation
#define EXI_BASETYPES_MAX_OCTETS_SUPPORTED 29

#define EXI_BASETYPES_OCTET_SEQ_FLAG_MASK 0x80
Expand Down
8 changes: 7 additions & 1 deletion src/input/code_templates/c/static_code/exi_basetypes_decoder.c.jinja
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Expand Up @@ -357,7 +357,13 @@ int exi_basetypes_decoder_signed(exi_bitstream_t* stream, exi_signed_t* value)
}
value->is_negative = (sign == 0) ? 0 : 1;

error = exi_basetypes_decoder_unsigned(stream, &value->data);
exi_unsigned_t raw_value;
error = exi_basetypes_decoder_unsigned(stream, &raw_value);
if (error != EXI_ERROR__NO_ERROR)
{
return error;
}
error = exi_basetypes_convert_bytes_from_unsigned(&raw_value, value->data.octets, &value->data.octets_count, sizeof(raw_value.octets));
return error;
}

Expand Down
11 changes: 10 additions & 1 deletion src/input/code_templates/c/static_code/exi_basetypes_encoder.c.jinja
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Expand Up @@ -175,7 +175,16 @@ int exi_basetypes_encoder_uint_64(exi_bitstream_t* stream, uint64_t value)

int exi_basetypes_encoder_unsigned(exi_bitstream_t* stream, const exi_unsigned_t* value)
{
return exi_basetypes_encoder_write_unsigned(stream, value);
int error;
exi_unsigned_t raw_exi_unsigned;

error = exi_basetypes_convert_bytes_from_unsigned(value, raw_exi_unsigned.octets, &raw_exi_unsigned.octets_count, sizeof(value->octets));
if (error != EXI_ERROR__NO_ERROR)
{
return error;
}

return exi_basetypes_encoder_write_unsigned(stream, &raw_exi_unsigned);
}

/*****************************************************************************
Expand Down