A variable-length integer,
in the format used by the 0xfe chunks in the 'dcmp' (0) and 'dcmp' (1) resource compression formats.
See the dcmp_0 and dcmp_1 specs for more information about these compression formats.
This variable-length integer format can store an integer x in any of the following ways:
0 <= x <= 0x7f
(7-bit unsigned integer)-0x4000 <= x <= 0x3eff
(15-bit signed integer with the highest 0x100 values unavailable)-0x80000000 <= x <= 0x7fffffff
(32-bit signed integer)In practice, values are always stored in the smallest possible format, but technically any of the larger formats could be used as well.
This page hosts a formal specification of Variable-length integer used in Apple `'dcmp' (0)` and `'dcmp' (1)` compressed resource formats using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for C++98/STL generated by Kaitai Struct depends on the C++/STL runtime library. You have to install it before you can parse data.
For C++, the easiest way is to clone the runtime library sources and build them along with your project.
Using Kaitai Struct in C++/STL usually consists of 3 steps.
std::istream). One can open local file for that, or use existing std::string or char* buffer.
#include <fstream>
std::ifstream is("path/to/local/file.bin", std::ifstream::binary);
#include <sstream>
std::istringstream is(str);
#include <sstream>
const char buf[] = { ... };
std::string str(buf, sizeof buf);
std::istringstream is(str);
#include "kaitai/kaitaistream.h"
kaitai::kstream ks(&is);
dcmp_variable_length_integer_t data(&ks);
After that, one can get various attributes from the structure by invoking getter methods like:
data.first() // => The first byte of the variable-length integer.
This determines which storage format is used.
* For the 1-byte format,
this encodes the entire value of the value.
* For the 2-byte format,
this encodes the high 7 bits of the value,
minus `0xc0`.
The highest bit of the value,
i. e. the second-highest bit of this field,
is the sign bit.
* For the 5-byte format,
this is always `0xff`.
data.value() // => The decoded value of the variable-length integer.
#ifndef DCMP_VARIABLE_LENGTH_INTEGER_H_
#define DCMP_VARIABLE_LENGTH_INTEGER_H_
// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
#include "kaitai/kaitaistruct.h"
#include <stdint.h>
#if KAITAI_STRUCT_VERSION < 9000L
#error "Incompatible Kaitai Struct C++/STL API: version 0.9 or later is required"
#endif
/**
* A variable-length integer,
* in the format used by the 0xfe chunks in the `'dcmp' (0)` and `'dcmp' (1)` resource compression formats.
* See the dcmp_0 and dcmp_1 specs for more information about these compression formats.
*
* This variable-length integer format can store an integer `x` in any of the following ways:
*
* * In a single byte,
* if `0 <= x <= 0x7f`
* (7-bit unsigned integer)
* * In 2 bytes,
* if `-0x4000 <= x <= 0x3eff`
* (15-bit signed integer with the highest `0x100` values unavailable)
* * In 5 bytes, if `-0x80000000 <= x <= 0x7fffffff`
* (32-bit signed integer)
*
* In practice,
* values are always stored in the smallest possible format,
* but technically any of the larger formats could be used as well.
* \sa https://github.com/dgelessus/python-rsrcfork/blob/f891a6e/src/rsrcfork/compress/common.py Source
*/
class dcmp_variable_length_integer_t : public kaitai::kstruct {
public:
dcmp_variable_length_integer_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent = 0, dcmp_variable_length_integer_t* p__root = 0);
private:
void _read();
void _clean_up();
public:
~dcmp_variable_length_integer_t();
private:
bool f_value;
int32_t m_value;
public:
/**
* The decoded value of the variable-length integer.
*/
int32_t value();
private:
uint8_t m_first;
int32_t m_more;
bool n_more;
public:
bool _is_null_more() { more(); return n_more; };
private:
dcmp_variable_length_integer_t* m__root;
kaitai::kstruct* m__parent;
public:
/**
* The first byte of the variable-length integer.
* This determines which storage format is used.
*
* * For the 1-byte format,
* this encodes the entire value of the value.
* * For the 2-byte format,
* this encodes the high 7 bits of the value,
* minus `0xc0`.
* The highest bit of the value,
* i. e. the second-highest bit of this field,
* is the sign bit.
* * For the 5-byte format,
* this is always `0xff`.
*/
uint8_t first() const { return m_first; }
/**
* The remaining bytes of the variable-length integer.
*
* * For the 1-byte format,
* this is not present.
* * For the 2-byte format,
* this encodes the low 8 bits of the value.
* * For the 5-byte format,
* this encodes the entire value.
*/
int32_t more() const { return m_more; }
dcmp_variable_length_integer_t* _root() const { return m__root; }
kaitai::kstruct* _parent() const { return m__parent; }
};
#endif // DCMP_VARIABLE_LENGTH_INTEGER_H_
// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
#include "dcmp_variable_length_integer.h"
dcmp_variable_length_integer_t::dcmp_variable_length_integer_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent, dcmp_variable_length_integer_t* p__root) : kaitai::kstruct(p__io) {
m__parent = p__parent;
m__root = this;
f_value = false;
try {
_read();
} catch(...) {
_clean_up();
throw;
}
}
void dcmp_variable_length_integer_t::_read() {
m_first = m__io->read_u1();
n_more = true;
if (first() >= 128) {
n_more = false;
switch (first()) {
case 255: {
m_more = m__io->read_s4be();
break;
}
default: {
m_more = m__io->read_u1();
break;
}
}
}
}
dcmp_variable_length_integer_t::~dcmp_variable_length_integer_t() {
_clean_up();
}
void dcmp_variable_length_integer_t::_clean_up() {
if (!n_more) {
}
}
int32_t dcmp_variable_length_integer_t::value() {
if (f_value)
return m_value;
m_value = ((first() == 255) ? (more()) : (((first() >= 128) ? ((((first() << 8) | more()) - 49152)) : (first()))));
f_value = true;
return m_value;
}