Modules/_struct.c

/* struct module -- pack values into and (out of) strings */

/* New version supporting byte order, alignment and size options,
   character strings, and unsigned numbers */

#include "Python.h"
#include "structseq.h"
#include "structmember.h"
#include <ctype.h>

static PyTypeObject PyStructType;

/* compatibility macros */
#if (PY_VERSION_HEX < 0x02050000)
typedef int Py_ssize_t;
#endif


/* PY_USE_INT_WHEN_POSSIBLE is an experimental flag that changes the 
   struct API to return int instead of long when possible. This is
   often a significant performance improvement. */
/*
#define PY_USE_INT_WHEN_POSSIBLE 1
*/

/* PY_STRUCT_RANGE_CHECKING performs range checking on all arguments
   to be packed. This will break some incorrect code that happened
   to accidentally do the right thing anyway (such as binhex). */
#define PY_STRUCT_RANGE_CHECKING 1

/* The translation function for each format character is table driven */
typedef struct _formatdef {
	char format;
	int size;
	int alignment;
	PyObject* (*unpack)(const char *,
			    const struct _formatdef *);
	int (*pack)(char *, PyObject *,
		    const struct _formatdef *);
} formatdef;

typedef struct _formatcode {
	const struct _formatdef *fmtdef;
	int offset;
	int size;
} formatcode;

/* Struct object interface */

typedef struct {
	PyObject_HEAD
	int s_size;
	int s_len;
	formatcode *s_codes;
	PyObject *s_format;
	PyObject *weakreflist; /* List of weak references */
} PyStructObject;


#define PyStruct_Check(op) PyObject_TypeCheck(op, &PyStructType)
#define PyStruct_CheckExact(op) ((op)->ob_type == &PyStructType)


/* Exception */

static PyObject *StructError;


/* Define various structs to figure out the alignments of types */


typedef struct { char c; short x; } st_short;
typedef struct { char c; int x; } st_int;
typedef struct { char c; long x; } st_long;
typedef struct { char c; float x; } st_float;
typedef struct { char c; double x; } st_double;
typedef struct { char c; void *x; } st_void_p;

#define SHORT_ALIGN (sizeof(st_short) - sizeof(short))
#define INT_ALIGN (sizeof(st_int) - sizeof(int))
#define LONG_ALIGN (sizeof(st_long) - sizeof(long))
#define FLOAT_ALIGN (sizeof(st_float) - sizeof(float))
#define DOUBLE_ALIGN (sizeof(st_double) - sizeof(double))
#define VOID_P_ALIGN (sizeof(st_void_p) - sizeof(void *))

/* We can't support q and Q in native mode unless the compiler does;
   in std mode, they're 8 bytes on all platforms. */
#ifdef HAVE_LONG_LONG
typedef struct { char c; PY_LONG_LONG x; } s_long_long;
#define LONG_LONG_ALIGN (sizeof(s_long_long) - sizeof(PY_LONG_LONG))
#endif

#define STRINGIFY(x)    #x

#ifdef __powerc
#pragma options align=reset
#endif

/* Helper to get a PyLongObject by hook or by crook.  Caller should decref. */

static PyObject *
get_pylong(PyObject *v)
{
	PyNumberMethods *m;

	assert(v != NULL);
	if (PyInt_Check(v))
		return PyLong_FromLong(PyInt_AS_LONG(v));
	if (PyLong_Check(v)) {
		Py_INCREF(v);
		return v;
	}
	m = v->ob_type->tp_as_number;
	if (m != NULL && m->nb_long != NULL) {
		v = m->nb_long(v);
		if (v == NULL)
			return NULL;
		if (PyLong_Check(v))
			return v;
		Py_DECREF(v);
	}
	PyErr_SetString(StructError,
			"cannot convert argument to long");
	return NULL;
}

/* Helper routine to get a Python integer and raise the appropriate error
   if it isn't one */

static int
get_long(PyObject *v, long *p)
{
	long x = PyInt_AsLong(v);
	if (x == -1 && PyErr_Occurred()) {
		if (PyErr_ExceptionMatches(PyExc_TypeError))
			PyErr_SetString(StructError,
					"required argument is not an integer");
		return -1;
	}
	*p = x;
	return 0;
}


/* Same, but handling unsigned long */

static int
get_ulong(PyObject *v, unsigned long *p)
{
	if (PyLong_Check(v)) {
		unsigned long x = PyLong_AsUnsignedLong(v);
		if (x == (unsigned long)(-1) && PyErr_Occurred())
			return -1;
		*p = x;
		return 0;
	}
	if (get_long(v, (long *)p) < 0)
		return -1;
	if (((long)*p) < 0) {
		PyErr_SetString(StructError,
				"unsigned argument is < 0");
		return -1;
	}
	return 0;
}

#ifdef HAVE_LONG_LONG

/* Same, but handling native long long. */

static int
get_longlong(PyObject *v, PY_LONG_LONG *p)
{
	PY_LONG_LONG x;

	v = get_pylong(v);
	if (v == NULL)
		return -1;
	assert(PyLong_Check(v));
	x = PyLong_AsLongLong(v);
	Py_DECREF(v);
	if (x == (PY_LONG_LONG)-1 && PyErr_Occurred())
		return -1;
	*p = x;
	return 0;
}

/* Same, but handling native unsigned long long. */

static int
get_ulonglong(PyObject *v, unsigned PY_LONG_LONG *p)
{
	unsigned PY_LONG_LONG x;

	v = get_pylong(v);
	if (v == NULL)
		return -1;
	assert(PyLong_Check(v));
	x = PyLong_AsUnsignedLongLong(v);
	Py_DECREF(v);
	if (x == (unsigned PY_LONG_LONG)-1 && PyErr_Occurred())
		return -1;
	*p = x;
	return 0;
}

#endif

/* Floating point helpers */

static PyObject *
unpack_float(const char *p,  /* start of 4-byte string */
             int le)	     /* true for little-endian, false for big-endian */
{
	double x;

	x = _PyFloat_Unpack4((unsigned char *)p, le);
	if (x == -1.0 && PyErr_Occurred())
		return NULL;
	return PyFloat_FromDouble(x);
}

static PyObject *
unpack_double(const char *p,  /* start of 8-byte string */
              int le)         /* true for little-endian, false for big-endian */
{
	double x;

	x = _PyFloat_Unpack8((unsigned char *)p, le);
	if (x == -1.0 && PyErr_Occurred())
		return NULL;
	return PyFloat_FromDouble(x);
}

#ifdef PY_STRUCT_RANGE_CHECKING
/* Helper to format the range error exceptions */
static int
_range_error(char format, int size, int is_unsigned)
{
	if (is_unsigned == 0) {
		long smallest = 0, largest = 0;
		int i = size * 8;
		while (--i > 0) {
			smallest = (smallest * 2) - 1;
			largest = (largest * 2) + 1;
		}
		PyErr_Format(StructError,
			"'%c' format requires %ld <= number <= %ld",
			format,
			smallest,
			largest);
	} else {
		unsigned long largest = 0;
		int i = size * 8;
		while (--i >= 0)
			largest = (largest * 2) + 1;
		PyErr_Format(StructError,
			"'%c' format requires 0 <= number <= %lu",
			format,
			largest);
	}
	return -1;
}
#endif



/* A large number of small routines follow, with names of the form

	[bln][up]_TYPE

   [bln] distiguishes among big-endian, little-endian and native.
   [pu] distiguishes between pack (to struct) and unpack (from struct).
   TYPE is one of char, byte, ubyte, etc.
*/

/* Native mode routines. ****************************************************/
/* NOTE:
   In all n[up]_<type> routines handling types larger than 1 byte, there is
   *no* guarantee that the p pointer is properly aligned for each type,
   therefore memcpy is called.  An intermediate variable is used to
   compensate for big-endian architectures.
   Normally both the intermediate variable and the memcpy call will be
   skipped by C optimisation in little-endian architectures (gcc >= 2.91
   does this). */

static PyObject *
nu_char(const char *p, const formatdef *f)
{
	return PyString_FromStringAndSize(p, 1);
}

static PyObject *
nu_byte(const char *p, const formatdef *f)
{
	return PyInt_FromLong((long) *(signed char *)p);
}

static PyObject *
nu_ubyte(const char *p, const formatdef *f)
{
	return PyInt_FromLong((long) *(unsigned char *)p);
}

static PyObject *
nu_short(const char *p, const formatdef *f)
{
	short x;
	memcpy((char *)&x, p, sizeof x);
	return PyInt_FromLong((long)x);
}

static PyObject *
nu_ushort(const char *p, const formatdef *f)
{
	unsigned short x;
	memcpy((char *)&x, p, sizeof x);
	return PyInt_FromLong((long)x);
}

static PyObject *
nu_int(const char *p, const formatdef *f)
{
	int x;
	memcpy((char *)&x, p, sizeof x);
	return PyInt_FromLong((long)x);
}

static PyObject *
nu_uint(const char *p, const formatdef *f)
{
	unsigned int x;
	memcpy((char *)&x, p, sizeof x);
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x <= LONG_MAX)
		return PyInt_FromLong((long)x);
#endif
	return PyLong_FromUnsignedLong((unsigned long)x);
}

static PyObject *
nu_long(const char *p, const formatdef *f)
{
	long x;
	memcpy((char *)&x, p, sizeof x);
	return PyInt_FromLong(x);
}

static PyObject *
nu_ulong(const char *p, const formatdef *f)
{
	unsigned long x;
	memcpy((char *)&x, p, sizeof x);
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x <= LONG_MAX)
		return PyInt_FromLong((long)x);
#endif
	return PyLong_FromUnsignedLong(x);
}

/* Native mode doesn't support q or Q unless the platform C supports
   long long (or, on Windows, __int64). */

#ifdef HAVE_LONG_LONG

static PyObject *
nu_longlong(const char *p, const formatdef *f)
{
	PY_LONG_LONG x;
	memcpy((char *)&x, p, sizeof x);
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x >= LONG_MIN && x <= LONG_MAX)
		return PyInt_FromLong(Py_SAFE_DOWNCAST(x, PY_LONG_LONG, long));
#endif
	return PyLong_FromLongLong(x);
}

static PyObject *
nu_ulonglong(const char *p, const formatdef *f)
{
	unsigned PY_LONG_LONG x;
	memcpy((char *)&x, p, sizeof x);
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x <= LONG_MAX)
		return PyInt_FromLong(Py_SAFE_DOWNCAST(x, unsigned PY_LONG_LONG, long));
#endif
	return PyLong_FromUnsignedLongLong(x);
}

#endif

static PyObject *
nu_float(const char *p, const formatdef *f)
{
	float x;
	memcpy((char *)&x, p, sizeof x);
	return PyFloat_FromDouble((double)x);
}

static PyObject *
nu_double(const char *p, const formatdef *f)
{
	double x;
	memcpy((char *)&x, p, sizeof x);
	return PyFloat_FromDouble(x);
}

static PyObject *
nu_void_p(const char *p, const formatdef *f)
{
	void *x;
	memcpy((char *)&x, p, sizeof x);
	return PyLong_FromVoidPtr(x);
}

static int
np_byte(char *p, PyObject *v, const formatdef *f)
{
	long x;
	if (get_long(v, &x) < 0)
		return -1;
	if (x < -128 || x > 127){
		PyErr_SetString(StructError,
				"byte format requires -128 <= number <= 127");
		return -1;
	}
	*p = (char)x;
	return 0;
}

static int
np_ubyte(char *p, PyObject *v, const formatdef *f)
{
	long x;
	if (get_long(v, &x) < 0)
		return -1;
	if (x < 0 || x > 255){
		PyErr_SetString(StructError,
				"ubyte format requires 0 <= number <= 255");
		return -1;
	}
	*p = (char)x;
	return 0;
}

static int
np_char(char *p, PyObject *v, const formatdef *f)
{
	if (!PyString_Check(v) || PyString_Size(v) != 1) {
		PyErr_SetString(StructError,
				"char format require string of length 1");
		return -1;
	}
	*p = *PyString_AsString(v);
	return 0;
}

static int
np_short(char *p, PyObject *v, const formatdef *f)
{
	long x;
	short y;
	if (get_long(v, &x) < 0)
		return -1;
	if (x < SHRT_MIN || x > SHRT_MAX){
		PyErr_SetString(StructError,
				"short format requires " STRINGIFY(SHRT_MIN)
				" <= number <= " STRINGIFY(SHRT_MAX));
		return -1;
	}
	y = (short)x;
	memcpy(p, (char *)&y, sizeof y);
	return 0;
}

static int
np_ushort(char *p, PyObject *v, const formatdef *f)
{
	long x;
	unsigned short y;
	if (get_long(v, &x) < 0)
		return -1;
	if (x < 0 || x > USHRT_MAX){
		PyErr_SetString(StructError,
				"short format requires 0 <= number <= " STRINGIFY(USHRT_MAX));
		return -1;
	}
	y = (unsigned short)x;
	memcpy(p, (char *)&y, sizeof y);
	return 0;
}

static int
np_int(char *p, PyObject *v, const formatdef *f)
{
	long x;
	int y;
	if (get_long(v, &x) < 0)
		return -1;
#if defined(PY_STRUCT_RANGE_CHECKING) && (SIZEOF_LONG > SIZEOF_INT)
	if (x < INT_MIN || x > INT_MAX)
		return _range_error(f->format, sizeof(y), 0);
#endif
	y = (int)x;
	memcpy(p, (char *)&y, sizeof y);
	return 0;
}

static int
np_uint(char *p, PyObject *v, const formatdef *f)
{
	unsigned long x;
	unsigned int y;
	if (get_ulong(v, &x) < 0)
#ifdef PY_STRUCT_RANGE_CHECKING
		return _range_error(f->format, sizeof(y), 1);
#else
		return -1;
#endif
	y = (unsigned int)x;
#if defined(PY_STRUCT_RANGE_CHECKING) && (SIZEOF_LONG > SIZEOF_INT)
	if (x < UINT_MIN || x > UINT_MAX)
		return _range_error(f->format, sizeof(y), 1);
#endif
	memcpy(p, (char *)&y, sizeof y);
	return 0;
}

static int
np_long(char *p, PyObject *v, const formatdef *f)
{
	long x;
	if (get_long(v, &x) < 0)
		return -1;
	memcpy(p, (char *)&x, sizeof x);
	return 0;
}

static int
np_ulong(char *p, PyObject *v, const formatdef *f)
{
	unsigned long x;
	if (get_ulong(v, &x) < 0)
#ifdef PY_STRUCT_RANGE_CHECKING
		return _range_error(f->format, sizeof(x), 1);
#else
		return -1;
#endif
	memcpy(p, (char *)&x, sizeof x);
	return 0;
}

#ifdef HAVE_LONG_LONG

static int
np_longlong(char *p, PyObject *v, const formatdef *f)
{
	PY_LONG_LONG x;
	if (get_longlong(v, &x) < 0)
		return -1;
	memcpy(p, (char *)&x, sizeof x);
	return 0;
}

static int
np_ulonglong(char *p, PyObject *v, const formatdef *f)
{
	unsigned PY_LONG_LONG x;
	if (get_ulonglong(v, &x) < 0)
		return -1;
	memcpy(p, (char *)&x, sizeof x);
	return 0;
}
#endif

static int
np_float(char *p, PyObject *v, const formatdef *f)
{
	float x = (float)PyFloat_AsDouble(v);
	if (x == -1 && PyErr_Occurred()) {
		PyErr_SetString(StructError,
				"required argument is not a float");
		return -1;
	}
	memcpy(p, (char *)&x, sizeof x);
	return 0;
}

static int
np_double(char *p, PyObject *v, const formatdef *f)
{
	double x = PyFloat_AsDouble(v);
	if (x == -1 && PyErr_Occurred()) {
		PyErr_SetString(StructError,
				"required argument is not a float");
		return -1;
	}
	memcpy(p, (char *)&x, sizeof(double));
	return 0;
}

static int
np_void_p(char *p, PyObject *v, const formatdef *f)
{
	void *x;

	v = get_pylong(v);
	if (v == NULL)
		return -1;
	assert(PyLong_Check(v));
	x = PyLong_AsVoidPtr(v);
	Py_DECREF(v);
	if (x == NULL && PyErr_Occurred())
		return -1;
	memcpy(p, (char *)&x, sizeof x);
	return 0;
}

static formatdef native_table[] = {
	{'x',	sizeof(char),	0,		NULL},
	{'b',	sizeof(char),	0,		nu_byte,	np_byte},
	{'B',	sizeof(char),	0,		nu_ubyte,	np_ubyte},
	{'c',	sizeof(char),	0,		nu_char,	np_char},
	{'s',	sizeof(char),	0,		NULL},
	{'p',	sizeof(char),	0,		NULL},
	{'h',	sizeof(short),	SHORT_ALIGN,	nu_short,	np_short},
	{'H',	sizeof(short),	SHORT_ALIGN,	nu_ushort,	np_ushort},
	{'i',	sizeof(int),	INT_ALIGN,	nu_int,		np_int},
	{'I',	sizeof(int),	INT_ALIGN,	nu_uint,	np_uint},
	{'l',	sizeof(long),	LONG_ALIGN,	nu_long,	np_long},
	{'L',	sizeof(long),	LONG_ALIGN,	nu_ulong,	np_ulong},
#ifdef HAVE_LONG_LONG
	{'q',	sizeof(PY_LONG_LONG), LONG_LONG_ALIGN, nu_longlong, np_longlong},
	{'Q',	sizeof(PY_LONG_LONG), LONG_LONG_ALIGN, nu_ulonglong,np_ulonglong},
#endif
	{'f',	sizeof(float),	FLOAT_ALIGN,	nu_float,	np_float},
	{'d',	sizeof(double),	DOUBLE_ALIGN,	nu_double,	np_double},
	{'P',	sizeof(void *),	VOID_P_ALIGN,	nu_void_p,	np_void_p},
	{0}
};

/* Big-endian routines. *****************************************************/

static PyObject *
bu_int(const char *p, const formatdef *f)
{
	long x = 0;
	int i = f->size;
	do {
		x = (x<<8) | (*p++ & 0xFF);
	} while (--i > 0);
	/* Extend the sign bit. */
	if (SIZEOF_LONG > f->size)
		x |= -(x & (1L << (8*f->size - 1)));
	return PyInt_FromLong(x);
}

static PyObject *
bu_uint(const char *p, const formatdef *f)
{
	unsigned long x = 0;
	int i = f->size;
	do {
		x = (x<<8) | (*p++ & 0xFF);
	} while (--i > 0);
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x <= LONG_MAX)
		return PyInt_FromLong((long)x);
#else
	if (SIZEOF_LONG > f->size)
		return PyInt_FromLong((long)x);
#endif
	return PyLong_FromUnsignedLong(x);
}

static PyObject *
bu_longlong(const char *p, const formatdef *f)
{
#if HAVE_LONG_LONG
	PY_LONG_LONG x = 0;
	int i = f->size;
	do {
		x = (x<<8) | (*p++ & 0xFF);
	} while (--i > 0);
	/* Extend the sign bit. */
	if (SIZEOF_LONG_LONG > f->size)
		x |= -(x & (1L << (8 * f->size - 1)));
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x >= LONG_MIN && x <= LONG_MAX)
		return PyInt_FromLong(Py_SAFE_DOWNCAST(x, PY_LONG_LONG, long));
#endif
	return PyLong_FromLongLong(x);
#else
	return _PyLong_FromByteArray((const unsigned char *)p,
				      8,
				      0, /* little-endian */
				      1  /* signed */);
#endif
}

static PyObject *
bu_ulonglong(const char *p, const formatdef *f)
{
#if HAVE_LONG_LONG
	unsigned PY_LONG_LONG x = 0;
	int i = f->size;
	do {
		x = (x<<8) | (*p++ & 0xFF);
	} while (--i > 0);
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x <= LONG_MAX)
		return PyInt_FromLong(Py_SAFE_DOWNCAST(x, unsigned PY_LONG_LONG, long));
#endif
	return PyLong_FromUnsignedLongLong(x);
#else
	return _PyLong_FromByteArray((const unsigned char *)p,
				      8,
				      0, /* little-endian */
				      0  /* signed */);
#endif
}

static PyObject *
bu_float(const char *p, const formatdef *f)
{
	return unpack_float(p, 0);
}

static PyObject *
bu_double(const char *p, const formatdef *f)
{
	return unpack_double(p, 0);
}

static int
bp_int(char *p, PyObject *v, const formatdef *f)
{
	long x;
	int i;
	if (get_long(v, &x) < 0)
		return -1;
	i = f->size;
#ifdef PY_STRUCT_RANGE_CHECKING
	if (i != SIZEOF_LONG && (
		(i == 2 && (x < -32768 || x > 32767))
#if SIZEOF_LONG != 4
		|| (i == 4) && (x < -2147483648L || x > -2147483647L)
#endif
		))
		return _range_error(f->format, i, 0);
#endif
	do {
		p[--i] = (char)x;
		x >>= 8;
	} while (i > 0);
	return 0;
}

static int
bp_uint(char *p, PyObject *v, const formatdef *f)
{
	unsigned long x;
	int i;
	if (get_ulong(v, &x) < 0)
		return -1;
	i = f->size;
#ifdef PY_STRUCT_RANGE_CHECKING
	if (i != SIZEOF_LONG && x >= (1 << (i * 8)))
		return _range_error(f->format, f->size, 1);
#endif
	do {
		p[--i] = (char)x;
		x >>= 8;
	} while (i > 0);
	return 0;
}

static int
bp_longlong(char *p, PyObject *v, const formatdef *f)
{
	int res;
	v = get_pylong(v);
	if (v == NULL)
		return -1;
	res = _PyLong_AsByteArray((PyLongObject *)v,
			   	  (unsigned char *)p,
				  8,
				  0, /* little_endian */
				  1  /* signed */);
	Py_DECREF(v);
	return res;
}

static int
bp_ulonglong(char *p, PyObject *v, const formatdef *f)
{
	int res;
	v = get_pylong(v);
	if (v == NULL)
		return -1;
	res = _PyLong_AsByteArray((PyLongObject *)v,
			   	  (unsigned char *)p,
				  8,
				  0, /* little_endian */
				  0  /* signed */);
	Py_DECREF(v);
	return res;
}

static int
bp_float(char *p, PyObject *v, const formatdef *f)
{
	double x = PyFloat_AsDouble(v);
	if (x == -1 && PyErr_Occurred()) {
		PyErr_SetString(StructError,
				"required argument is not a float");
		return -1;
	}
	return _PyFloat_Pack4(x, (unsigned char *)p, 0);
}

static int
bp_double(char *p, PyObject *v, const formatdef *f)
{
	double x = PyFloat_AsDouble(v);
	if (x == -1 && PyErr_Occurred()) {
		PyErr_SetString(StructError,
				"required argument is not a float");
		return -1;
	}
	return _PyFloat_Pack8(x, (unsigned char *)p, 0);
}

static formatdef bigendian_table[] = {
	{'x',	1,		0,		NULL},
	{'b',	1,		0,		nu_byte,	np_byte},
	{'B',	1,		0,		nu_ubyte,	np_ubyte},
	{'c',	1,		0,		nu_char,	np_char},
	{'s',	1,		0,		NULL},
	{'p',	1,		0,		NULL},
	{'h',	2,		0,		bu_int,		bp_int},
	{'H',	2,		0,		bu_uint,	bp_uint},
	{'i',	4,		0,		bu_int,		bp_int},
	{'I',	4,		0,		bu_uint,	bp_uint},
	{'l',	4,		0,		bu_int,		bp_int},
	{'L',	4,		0,		bu_uint,	bp_uint},
	{'q',	8,		0,		bu_longlong,	bp_longlong},
	{'Q',	8,		0,		bu_ulonglong,	bp_ulonglong},
	{'f',	4,		0,		bu_float,	bp_float},
	{'d',	8,		0,		bu_double,	bp_double},
	{0}
};

/* Little-endian routines. *****************************************************/

static PyObject *
lu_int(const char *p, const formatdef *f)
{
	long x = 0;
	int i = f->size;
	do {
		x = (x<<8) | (p[--i] & 0xFF);
	} while (i > 0);
	/* Extend the sign bit. */
	if (SIZEOF_LONG > f->size)
		x |= -(x & (1L << (8*f->size - 1)));
	return PyInt_FromLong(x);
}

static PyObject *
lu_uint(const char *p, const formatdef *f)
{
	unsigned long x = 0;
	int i = f->size;
	do {
		x = (x<<8) | (p[--i] & 0xFF);
	} while (i > 0);
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x <= LONG_MAX)
		return PyInt_FromLong((long)x);
#else
	if (SIZEOF_LONG > f->size)
		return PyInt_FromLong((long)x);
#endif
	return PyLong_FromUnsignedLong((long)x);
}

static PyObject *
lu_longlong(const char *p, const formatdef *f)
{
#if HAVE_LONG_LONG
	PY_LONG_LONG x = 0;
	int i = f->size;
	do {
		x = (x<<8) | (p[--i] & 0xFF);
	} while (i > 0);
	/* Extend the sign bit. */
	if (SIZEOF_LONG_LONG > f->size)
		x |= -(x & (1L << (8 * f->size - 1)));
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x >= LONG_MIN && x <= LONG_MAX)
		return PyInt_FromLong(Py_SAFE_DOWNCAST(x, PY_LONG_LONG, long));
#endif
	return PyLong_FromLongLong(x);
#else
	return _PyLong_FromByteArray((const unsigned char *)p,
				      8,
				      1, /* little-endian */
				      1  /* signed */);
#endif
}

static PyObject *
lu_ulonglong(const char *p, const formatdef *f)
{
#if HAVE_LONG_LONG
	unsigned PY_LONG_LONG x = 0;
	int i = f->size;
	do {
		x = (x<<8) | (p[--i] & 0xFF);
	} while (i > 0);
#ifdef PY_USE_INT_WHEN_POSSIBLE
	if (x <= LONG_MAX)
		return PyInt_FromLong(Py_SAFE_DOWNCAST(x, unsigned PY_LONG_LONG, long));
#endif
	return PyLong_FromUnsignedLongLong(x);
#else
	return _PyLong_FromByteArray((const unsigned char *)p,
				      8,
				      1, /* little-endian */
				      0  /* signed */);
#endif
}

static PyObject *
lu_float(const char *p, const formatdef *f)
{
	return unpack_float(p, 1);
}

static PyObject *
lu_double(const char *p, const formatdef *f)
{
	return unpack_double(p, 1);
}

static int
lp_int(char *p, PyObject *v, const formatdef *f)
{
	long x;
	int i;
	if (get_long(v, &x) < 0)
		return -1;
	i = f->size;
#ifdef PY_STRUCT_RANGE_CHECKING
	if (i != SIZEOF_LONG && (
		(i == 2 && (x < -32768 || x > 32767))
#if SIZEOF_LONG != 4
		|| (i == 4) && (x < -2147483648L || x > -2147483647L)
#endif
		))
		return _range_error(f->format, i, 0);
#endif
	do {
		*p++ = (char)x;
		x >>= 8;
	} while (--i > 0);
	return 0;
}

static int
lp_uint(char *p, PyObject *v, const formatdef *f)
{
	unsigned long x;
	int i;
	if (get_ulong(v, &x) < 0)
		return -1;
	i = f->size;
#ifdef PY_STRUCT_RANGE_CHECKING
	if (i != SIZEOF_LONG && x >= (1 << (i * 8)))
		return _range_error(f->format, f->size, 1);
#endif
	do {
		*p++ = (char)x;
		x >>= 8;
	} while (--i > 0);
	return 0;
}

static int
lp_longlong(char *p, PyObject *v, const formatdef *f)
{
	int res;
	v = get_pylong(v);
	if (v == NULL)
		return -1;
	res = _PyLong_AsByteArray((PyLongObject*)v,
			   	  (unsigned char *)p,
				  8,
				  1, /* little_endian */
				  1  /* signed */);
	Py_DECREF(v);
	return res;
}

static int
lp_ulonglong(char *p, PyObject *v, const formatdef *f)
{
	int res;
	v = get_pylong(v);
	if (v == NULL)
		return -1;
	res = _PyLong_AsByteArray((PyLongObject*)v,
			   	  (unsigned char *)p,
				  8,
				  1, /* little_endian */
				  0  /* signed */);
	Py_DECREF(v);
	return res;
}

static int
lp_float(char *p, PyObject *v, const formatdef *f)
{
	double x = PyFloat_AsDouble(v);
	if (x == -1 && PyErr_Occurred()) {
		PyErr_SetString(StructError,
				"required argument is not a float");
		return -1;
	}
	return _PyFloat_Pack4(x, (unsigned char *)p, 1);
}

static int
lp_double(char *p, PyObject *v, const formatdef *f)
{
	double x = PyFloat_AsDouble(v);
	if (x == -1 && PyErr_Occurred()) {
		PyErr_SetString(StructError,
				"required argument is not a float");
		return -1;
	}
	return _PyFloat_Pack8(x, (unsigned char *)p, 1);
}

static formatdef lilendian_table[] = {
	{'x',	1,		0,		NULL},
	{'b',	1,		0,		nu_byte,	np_byte},
	{'B',	1,		0,		nu_ubyte,	np_ubyte},
	{'c',	1,		0,		nu_char,	np_char},
	{'s',	1,		0,		NULL},
	{'p',	1,		0,		NULL},
	{'h',	2,		0,		lu_int,		lp_int},
	{'H',	2,		0,		lu_uint,	lp_uint},
	{'i',	4,		0,		lu_int,		lp_int},
	{'I',	4,		0,		lu_uint,	lp_uint},
	{'l',	4,		0,		lu_int,		lp_int},
	{'L',	4,		0,		lu_uint,	lp_uint},
	{'q',	8,		0,		lu_longlong,	lp_longlong},
	{'Q',	8,		0,		lu_ulonglong,	lp_ulonglong},
	{'f',	4,		0,		lu_float,	lp_float},
	{'d',	8,		0,		lu_double,	lp_double},
	{0}
};


static const formatdef *
whichtable(char **pfmt)
{
	const char *fmt = (*pfmt)++; /* May be backed out of later */
	switch (*fmt) {
	case '<':
		return lilendian_table;
	case '>':
	case '!': /* Network byte order is big-endian */
		return bigendian_table;
	case '=': { /* Host byte order -- different from native in aligment! */
		int n = 1;
		char *p = (char *) &n;
		if (*p == 1)
			return lilendian_table;
		else
			return bigendian_table;
	}
	default:
		--*pfmt; /* Back out of pointer increment */
		/* Fall through */
	case '@':
		return native_table;
	}
}


/* Get the table entry for a format code */

static const formatdef *
getentry(int c, const formatdef *f)
{
	for (; f->format != '\0'; f++) {
		if (f->format == c) {
			return f;
		}
	}
	PyErr_SetString(StructError, "bad char in struct format");
	return NULL;
}


/* Align a size according to a format code */

static int
align(int size, int c, const formatdef *e)
{
	if (e->format == c) {
		if (e->alignment) {
			size = ((size + e->alignment - 1)
				/ e->alignment)
				* e->alignment;
		}
	}
	return size;
}


/* calculate the size of a format string */

static int
prepare_s(PyStructObject *self)
{
	const formatdef *f;
	const formatdef *e;
	formatcode *codes;
	
	const char *s;
	const char *fmt;
	char c;
	int size, len, num, itemsize, x;

	fmt = PyString_AS_STRING(self->s_format);

	f = whichtable((char **)&fmt);
	
	s = fmt;
	size = 0;
	len = 0;
	while ((c = *s++) != '\0') {
		if (isspace(Py_CHARMASK(c)))
			continue;
		if ('0' <= c && c <= '9') {
			num = c - '0';
			while ('0' <= (c = *s++) && c <= '9') {
				x = num*10 + (c - '0');
				if (x/10 != num) {
					PyErr_SetString(
						StructError,
						"overflow in item count");
					return -1;
				}
				num = x;
			}
			if (c == '\0')
				break;
		}
		else
			num = 1;

		e = getentry(c, f);
		if (e == NULL)
			return -1;
		
		switch (c) {
			case 's': /* fall through */
			case 'p': len++; break;
			case 'x': break;
			default: len += num; break;
		}

		itemsize = e->size;
		size = align(size, c, e);
		x = num * itemsize;
		size += x;
		if (x/itemsize != num || size < 0) {
			PyErr_SetString(StructError,
					"total struct size too long");
			return -1;
		}
	}

	self->s_size = size;
	self->s_len = len;
	codes = PyMem_MALLOC((len + 1) * sizeof(formatcode));
	if (codes == NULL) {
		PyErr_NoMemory();
		return -1;
	}
	self->s_codes = codes;
	
	s = fmt;
	size = 0;
	while ((c = *s++) != '\0') {
		if (isspace(Py_CHARMASK(c)))
			continue;
		if ('0' <= c && c <= '9') {
			num = c - '0';
			while ('0' <= (c = *s++) && c <= '9')
				num = num*10 + (c - '0');
			if (c == '\0')
				break;
		}
		else
			num = 1;

		e = getentry(c, f);
		
		size = align(size, c, e);
		if (c == 's' || c == 'p') {
			codes->offset = size;
			codes->size = num;
			codes->fmtdef = e;
			codes++;
			size += num;
		} else if (c == 'x') {
			size += num;
		} else {
			while (--num >= 0) {
				codes->offset = size;
				codes->size = e->size;
				codes->fmtdef = e;
				codes++;
				size += e->size;
			}
		}
	}
	codes->fmtdef = NULL;
	codes->offset = size;
	codes->size = 0;
	
	return 0;
}

static PyObject *
s_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
	PyObject *self;

	assert(type != NULL && type->tp_alloc != NULL);

	self = type->tp_alloc(type, 0);
	if (self != NULL) {
		PyStructObject *s = (PyStructObject*)self;
		Py_INCREF(Py_None);
		s->s_format = Py_None;
		s->s_codes = NULL;
		s->s_size = -1;
		s->s_len = -1;
	}
	return self;
}

static int
s_init(PyObject *self, PyObject *args, PyObject *kwds)
{
	PyStructObject *soself = (PyStructObject *)self;
	PyObject *o_format = NULL;
	int ret = 0;
	static char *kwlist[] = {"format", 0};

	assert(PyStruct_Check(self));

	if (!PyArg_ParseTupleAndKeywords(args, kwds, "S:Struct", kwlist,
					 &o_format))
        	return -1;

	Py_INCREF(o_format);
	Py_XDECREF(soself->s_format);
	soself->s_format = o_format;
	
	ret = prepare_s(soself);
	return ret;
}

static void
s_dealloc(PyStructObject *s)
{
	if (s->weakreflist != NULL)
		PyObject_ClearWeakRefs((PyObject *)s);
	if (s->s_codes != NULL) {
		PyMem_FREE(s->s_codes);
	}
	Py_XDECREF(s->s_format);
	s->ob_type->tp_free((PyObject *)s);
}

static PyObject *
s_unpack_internal(PyStructObject *soself, char *startfrom) {
	formatcode *code;
	Py_ssize_t i = 0;
	PyObject *result = PyTuple_New(soself->s_len);
	if (result == NULL)
		return NULL;

	for (code = soself->s_codes; code->fmtdef != NULL; code++) {
		PyObject *v;
		const formatdef *e = code->fmtdef;
		const char *res = startfrom + code->offset;
		if (e->format == 's') {
			v = PyString_FromStringAndSize(res, code->size);
			if (v == NULL)
				goto fail;
			PyTuple_SET_ITEM(result, i++, v);
		} else if (e->format == 'p') {
			Py_ssize_t n = *(unsigned char*)res;
			if (n >= code->size)
				n = code->size - 1;
			v = PyString_FromStringAndSize(res + 1, n);
			if (v == NULL)
				goto fail;
			PyTuple_SET_ITEM(result, i++, v);
		} else {
			v = e->unpack(res, e);
			if (v == NULL)
				goto fail;
			PyTuple_SET_ITEM(result, i++, v);
		}
	}

	return result;
fail:
	Py_DECREF(result);
	return NULL;
};


PyDoc_STRVAR(s_unpack__doc__,
"unpack(str) -> (v1, v2, ...)\n\
\n\
Return tuple containing values unpacked according to this Struct's format.\n\
Requires len(str) == self.size. See struct.__doc__ for more on format\n\
strings.");

static PyObject *
s_unpack(PyObject *self, PyObject *inputstr)
{
	PyStructObject *soself = (PyStructObject *)self;
	assert(PyStruct_Check(self));
	assert(soself->s_codes != NULL);	
	if (inputstr == NULL || !PyString_Check(inputstr) ||
		PyString_GET_SIZE(inputstr) != soself->s_size) {
		PyErr_Format(StructError,
			"unpack requires a string argument of length %d", soself->s_size);
		return NULL;
	}
	return s_unpack_internal(soself, PyString_AS_STRING(inputstr));
}

PyDoc_STRVAR(s_unpack_from__doc__,
"unpack_from(buffer[, offset]) -> (v1, v2, ...)\n\
\n\
Return tuple containing values unpacked according to this Struct's format.\n\
Unlike unpack, unpack_from can unpack values from any object supporting\n\
the buffer API, not just str. Requires len(buffer[offset:]) >= self.size.\n\
See struct.__doc__ for more on format strings.");

static PyObject *
s_unpack_from(PyObject *self, PyObject *args, PyObject *kwds)
{
	static char *kwlist[] = {"buffer", "offset", 0};
#if (PY_VERSION_HEX < 0x02050000)
	static char *fmt = "z#|i:unpack_from";
#else
	static char *fmt = "z#|n:unpack_from";
#endif
	Py_ssize_t buffer_len = 0, offset = 0;
	char *buffer = NULL;
	PyStructObject *soself = (PyStructObject *)self;
	assert(PyStruct_Check(self));
	assert(soself->s_codes != NULL);

	if (!PyArg_ParseTupleAndKeywords(args, kwds, fmt, kwlist,
					 &buffer, &buffer_len, &offset))
        	return NULL;

	if (buffer == NULL) {
		PyErr_Format(StructError,
			"unpack_from requires a buffer argument");
		return NULL;
	}
	
	if (offset < 0)
		offset += buffer_len;

	if (offset < 0 || (buffer_len - offset) < soself->s_size) {
		PyErr_Format(StructError,
			"unpack_from requires a buffer of at least %d bytes",
			soself->s_size);
		return NULL;
	}
	return s_unpack_internal(soself, buffer + offset);
}


/*
 * Guts of the pack function.
 *
 * Takes a struct object, a tuple of arguments, and offset in that tuple of
 * argument for where to start processing the arguments for packing, and a
 * character buffer for writing the packed string.  The caller must insure
 * that the buffer may contain the required length for packing the arguments.
 * 0 is returned on success, 1 is returned if there is an error.
 *
 */
static int
s_pack_internal(PyStructObject *soself, PyObject *args, int offset, char* buf)
{
	formatcode *code;
	Py_ssize_t i;

	memset(buf, '\0', soself->s_size);
	i = offset;
	for (code = soself->s_codes; code->fmtdef != NULL; code++) {
		Py_ssize_t n;
		PyObject *v;
		const formatdef *e = code->fmtdef;
		char *res = buf + code->offset;
		if (e->format == 's') {
			v = PyTuple_GET_ITEM(args, i++);
			if (!PyString_Check(v)) {
				PyErr_SetString(StructError,
						"argument for 's' must be a string");
				return -1;
			}
			n = PyString_GET_SIZE(v);
			if (n > code->size)
				n = code->size;
			if (n > 0)
				memcpy(res, PyString_AS_STRING(v), n);
		} else if (e->format == 'p') {
			v = PyTuple_GET_ITEM(args, i++);
			if (!PyString_Check(v)) {
				PyErr_SetString(StructError,
						"argument for 'p' must be a string");
				return -1;
			}
			n = PyString_GET_SIZE(v);
			if (n > (code->size - 1))
				n = code->size - 1;
			if (n > 0)
				memcpy(res + 1, PyString_AS_STRING(v), n);
			if (n > 255)
				n = 255;
			*res = Py_SAFE_DOWNCAST(n, Py_ssize_t, unsigned char);
		} else {
			v = PyTuple_GET_ITEM(args, i++);
			if (e->pack(res, v, e) < 0)
				return -1;
		}
	}
	
	/* Success */
	return 0;
}


PyDoc_STRVAR(s_pack__doc__,
"pack(v1, v2, ...) -> string\n\
\n\
Return a string containing values v1, v2, ... packed according to this\n\
Struct's format. See struct.__doc__ for more on format strings.");

static PyObject *
s_pack(PyObject *self, PyObject *args)
{
	PyStructObject *soself;
	PyObject *result;

	/* Validate arguments. */
	soself = (PyStructObject *)self;
	assert(PyStruct_Check(self));
	assert(soself->s_codes != NULL);
	if (args == NULL || !PyTuple_Check(args) ||
	    PyTuple_GET_SIZE(args) != soself->s_len)
	{
		PyErr_Format(StructError,
			"pack requires exactly %d arguments", soself->s_len);
		return NULL;
	}
	
	/* Allocate a new string */
	result = PyString_FromStringAndSize((char *)NULL, soself->s_size);
	if (result == NULL)
		return NULL;
	
	/* Call the guts */
	if ( s_pack_internal(soself, args, 0, PyString_AS_STRING(result)) != 0 ) {
		Py_DECREF(result);
		return NULL;
	}

	return result;
}

PyDoc_STRVAR(s_pack_to__doc__,
"pack_to(buffer, offset, v1, v2, ...)\n\
\n\
Pack the values v2, v2, ... according to this Struct's format, write \n\
the packed bytes into the given buffer at the given offset.  Note that \n\
the offset is not an optional argument.  See struct.__doc__ for \n\
more on format strings.");

static PyObject *
s_pack_to(PyObject *self, PyObject *args)
{
	PyStructObject *soself;
	char *buffer;
	Py_ssize_t buffer_len, offset;

	/* Validate arguments.  +1 is for the first arg as buffer. */
	soself = (PyStructObject *)self;
	assert(PyStruct_Check(self));
	assert(soself->s_codes != NULL);
	if (args == NULL || !PyTuple_Check(args) ||
	    PyTuple_GET_SIZE(args) != (soself->s_len + 2))
	{
		PyErr_Format(StructError,
			     "pack_to requires exactly %d arguments", 
			     (soself->s_len + 2));
		return NULL;
	}

	/* Extract a writable memory buffer from the first argument */
        if ( PyObject_AsWriteBuffer(PyTuple_GET_ITEM(args, 0), 
                                    (void**)&buffer, &buffer_len) == -1 ) { 
		return NULL;
        }
        assert( buffer_len >= 0 );

	/* Extract the offset from the first argument */
	offset = PyInt_AsLong(PyTuple_GET_ITEM(args, 1));

 	/* Support negative offsets. */
	if (offset < 0)
		offset += buffer_len;

	/* Check boundaries */
	if (offset < 0 || (buffer_len - offset) < soself->s_size) {
		PyErr_Format(StructError,
			     "pack_to requires a buffer of at least %d bytes",
			     soself->s_size);
		return NULL;
	}
	
	/* Call the guts */
	if ( s_pack_internal(soself, args, 2, buffer + offset) != 0 ) {
		return NULL;
	}

	return Py_None;
}


/* List of functions */

static struct PyMethodDef s_methods[] = {
	{"pack",	(PyCFunction)s_pack,		METH_VARARGS, s_pack__doc__},
 	{"pack_to",	(PyCFunction)s_pack_to,		METH_VARARGS, s_pack_to__doc__}, 
	{"unpack",	(PyCFunction)s_unpack,		METH_O, s_unpack__doc__},
	{"unpack_from",	(PyCFunction)s_unpack_from,	METH_KEYWORDS, s_unpack_from__doc__},
	{NULL,	 NULL}		/* sentinel */
};

PyDoc_STRVAR(s__doc__, "Compiled struct object");

#define OFF(x) offsetof(PyStructObject, x)

static PyMemberDef s_memberlist[] = {
	{"format",	T_OBJECT,	OFF(s_format),	RO,
	 "struct format string"},
	{"size",	T_INT,		OFF(s_size),	RO,
	 "struct size in bytes"},
	{"_len",	T_INT,		OFF(s_len),	RO,
	 "number of items expected in tuple"},
	{NULL}	/* Sentinel */
};


static
PyTypeObject PyStructType = {
	PyObject_HEAD_INIT(NULL)
	0,
	"Struct",
	sizeof(PyStructObject),
	0,
	(destructor)s_dealloc,			/* tp_dealloc */
	0,					/* tp_print */
	0,					/* tp_getattr */
	0,					/* tp_setattr */
	0,					/* tp_compare */
	0,					/* tp_repr */
	0,					/* tp_as_number */
	0,					/* tp_as_sequence */
	0,					/* tp_as_mapping */
	0,					/* tp_hash */
	0,					/* tp_call */
	0,					/* tp_str */
	PyObject_GenericGetAttr,		/* tp_getattro */
	PyObject_GenericSetAttr,		/* tp_setattro */
	0,					/* tp_as_buffer */
	Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_WEAKREFS, /* tp_flags */
	s__doc__,				/* tp_doc */
	0,					/* tp_traverse */
	0,					/* tp_clear */
	0,					/* tp_richcompare */
	offsetof(PyStructObject, weakreflist),	/* tp_weaklistoffset */
	0,					/* tp_iter */
	0,					/* tp_iternext */
	s_methods,				/* tp_methods */
	s_memberlist,				/* tp_members */
	0,					/* tp_getset */
	0,					/* tp_base */
	0,					/* tp_dict */
	0,					/* tp_descr_get */
	0,					/* tp_descr_set */
	0,					/* tp_dictoffset */
	s_init,					/* tp_init */
	PyType_GenericAlloc,			/* tp_alloc */
	s_new,					/* tp_new */
	PyObject_Del,				/* tp_free */
};

/* Module initialization */

PyMODINIT_FUNC
init_struct(void)
{
	PyObject *m = Py_InitModule("_struct", NULL);
	if (m == NULL)
		return;

	PyStructType.ob_type = &PyType_Type;
	if (PyType_Ready(&PyStructType) < 0)
		return;

	/* Check endian and swap in faster functions */
	{
		int one = 1;
		formatdef *native = native_table;
		formatdef *other, *ptr;
		if ((int)*(unsigned char*)&one)
			other = lilendian_table;
		else
			other = bigendian_table;
		/* Scan through the native table, find a matching
		   entry in the endian table and swap in the
		   native implementations whenever possible
		   (64-bit platforms may not have "standard" sizes) */
		while (native->format != '\0' && other->format != '\0') {
			ptr = other;
			while (ptr->format != '\0') {
				if (ptr->format == native->format) {
					/* Match faster when formats are
					   listed in the same order */
					if (ptr == other)
						other++;
					/* Only use the trick if the 
					   size matches */
					if (ptr->size != native->size)
						break;
					/* Skip float and double, could be
					   "unknown" float format */
					if (ptr->format == 'd' || ptr->format == 'f')
						break;
					ptr->pack = native->pack;
					ptr->unpack = native->unpack;
					break;
				}
				ptr++;
			}
			native++;
		}
	}
	
	/* Add some symbolic constants to the module */
	if (StructError == NULL) {
		StructError = PyErr_NewException("struct.error", NULL, NULL);
		if (StructError == NULL)
			return;
	}

	Py_INCREF(StructError);
	PyModule_AddObject(m, "error", StructError);

	Py_INCREF((PyObject*)&PyStructType);
	PyModule_AddObject(m, "Struct", (PyObject*)&PyStructType);
}