blob: c70a44ac41e4a93d2ad61653f8a8f9ca199447c0 [file] [log] [blame]
/*
* Author: Jeff Thompson
*
* BSD license, See the LICENSE file for more information.
*/
#include "BinaryXML.h"
#include "BinaryXMLEncoder.h"
enum {
ENCODING_LIMIT_1_BYTE = ((1 << ndn_BinaryXML_TT_VALUE_BITS) - 1),
ENCODING_LIMIT_2_BYTES = ((1 << (ndn_BinaryXML_TT_VALUE_BITS + ndn_BinaryXML_REGULAR_VALUE_BITS)) - 1),
ENCODING_LIMIT_3_BYTES = ((1 << (ndn_BinaryXML_TT_VALUE_BITS + 2 * ndn_BinaryXML_REGULAR_VALUE_BITS)) - 1)
};
/**
* Return the number of bytes to encode a header of value x.
*/
static unsigned int getNEncodingBytes(unsigned int x)
{
// Do a quick check for pre-compiled results.
if (x <= ENCODING_LIMIT_1_BYTE)
return 1;
if (x <= ENCODING_LIMIT_2_BYTES)
return 2;
if (x <= ENCODING_LIMIT_3_BYTES)
return 3;
unsigned int nBytes = 1;
// Last byte gives you TT_VALUE_BITS.
// Remainder each gives you REGULAR_VALUE_BITS.
x >>= ndn_BinaryXML_TT_VALUE_BITS;
while (x != 0) {
++nBytes;
x >>= ndn_BinaryXML_REGULAR_VALUE_BITS;
}
return nBytes;
}
char *ndn_BinaryXMLEncoder_encodeTypeAndValue(struct ndn_BinaryXMLEncoder *self, unsigned int type, unsigned int value)
{
if (type > ndn_BinaryXML_UDATA)
return "ndn_BinaryXMLEncoder_encodeTypeAndValue: type is out of range";
// Encode backwards. Calculate how many bytes we need.
unsigned int nEncodingBytes = getNEncodingBytes(value);
char *error;
if (error = ndn_DynamicUCharArray_ensureLength(&self->output, self->offset + nEncodingBytes))
return error;
// Bottom 4 bits of value go in last byte with tag.
self->output.array[self->offset + nEncodingBytes - 1] =
(ndn_BinaryXML_TT_MASK & type |
((ndn_BinaryXML_TT_VALUE_MASK & value) << ndn_BinaryXML_TT_BITS)) |
ndn_BinaryXML_TT_FINAL; // set top bit for last byte
value >>= ndn_BinaryXML_TT_VALUE_BITS;
// Rest of value goes into preceding bytes, 7 bits per byte. (Zero top bit is "more" flag.)
unsigned int i = self->offset + nEncodingBytes - 2;
while (value != 0 && i >= self->offset) {
self->output.array[i] = (value & ndn_BinaryXML_REGULAR_VALUE_MASK);
value >>= ndn_BinaryXML_REGULAR_VALUE_BITS;
--i;
}
if (value != 0)
// This should not happen if getNEncodingBytes is correct.
return "ndn_BinaryXMLEncoder_encodeTypeAndValue: : miscalculated N encoding bytes";
self->offset+= nEncodingBytes;
return 0;
}