patch #1493701: performance enhancements for struct module

Lib/struct.py

+"""
+Functions to convert between Python values and C structs.
+Python strings are used to hold the data representing the C struct
+and also as format strings to describe the layout of data in the C struct.
+
+The optional first format char indicates byte order, size and alignment:
+ @: native order, size & alignment (default)
+ =: native order, std. size & alignment
+ <: little-endian, std. size & alignment
+ >: big-endian, std. size & alignment
+ !: same as >
+
+The remaining chars indicate types of args and must match exactly;
+these can be preceded by a decimal repeat count:
+ x: pad byte (no data); c:char; b:signed byte; B:unsigned byte;
+ h:short; H:unsigned short; i:int; I:unsigned int;
+ l:long; L:unsigned long; f:float; d:double.
+Special cases (preceding decimal count indicates length):
+ s:string (array of char); p: pascal string (with count byte).
+Special case (only available in native format):
+ P:an integer type that is wide enough to hold a pointer.
+Special case (not in native mode unless 'long long' in platform C):
+ q:long long; Q:unsigned long long
+Whitespace between formats is ignored.
+
+The variable struct.error is an exception raised on errors.
+"""
+__version__ = '0.1'
+
+from _struct import Struct, error
+
+_MAXCACHE = 100
+_cache = {}
+
+def _compile(fmt):
+    # Internal: compile struct pattern
+    if len(_cache) >= _MAXCACHE:
+        _cache.clear()
+    s = Struct(fmt)
+    _cache[fmt] = s
+    return s
+
+def calcsize(fmt):
+    """
+    Return size of C struct described by format string fmt.
+    See struct.__doc__ for more on format strings.
+    """
+    try:
+        o = _cache[fmt]
+    except KeyError:
+        o = _compile(fmt)
+    return o.size
+    
+def pack(fmt, *args):
+    """
+    Return string containing values v1, v2, ... packed according to fmt.
+    See struct.__doc__ for more on format strings.
+    """
+    try:
+        o = _cache[fmt]
+    except KeyError:
+        o = _compile(fmt)
+    return o.pack(*args)
+
+def unpack(fmt, s):
+    """
+    Unpack the string, containing packed C structure data, according
+    to fmt.  Requires len(string)==calcsize(fmt).
+    See struct.__doc__ for more on format strings.
+    """
+    try:
+        o = _cache[fmt]
+    except KeyError:
+        o = _compile(fmt)
+    return o.unpack(s)
+    

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>
+
+
+/* compatibility macros */
+#if (PY_VERSION_HEX < 0x02050000)
+typedef int Py_ssize_t;
+#endif
+
+
+
+/* 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 repeat;
+} 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;
+
+PyAPI_DATA(PyTypeObject) PyStruct_Type;
+
+#define PyStruct_Check(op) PyObject_TypeCheck(op, &PyStruct_Type)
+#define PyStruct_CheckExact(op) ((op)->ob_type == &PyStruct_Type)
+
+
+/* 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;
+	}
+	else {
+		return get_long(v, (long *)p);
+	}
+}
+
+#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);
+}
+
+
+/* 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);
+	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);
+	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);
+	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);
+	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;
+	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)
+		return -1;
+	y = (unsigned int)x;
+	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)
+		return -1;
+	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},
+	{'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},
+#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
+	{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);
+	if (f->size >= 4)
+		return PyLong_FromUnsignedLong(x);
+	else
+		return PyInt_FromLong((long)x);
+}
+
+static PyObject *
+bu_longlong(const char *p, const formatdef *f)
+{
+	return _PyLong_FromByteArray((const unsigned char *)p,
+				      8,
+				      0, /* little-endian */
+				      1  /* signed */);
+}
+
+static PyObject *
+bu_ulonglong(const char *p, const formatdef *f)
+{
+	return _PyLong_FromByteArray((const unsigned char *)p,
+				      8,
+				      0, /* little-endian */
+				      0  /* signed */);
+}
+
+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;
+	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;
+	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,		bu_int,		bp_int},
+	{'B',	1,		0,		bu_uint,	bp_int},
+	{'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);
+	if (f->size >= 4)
+		return PyLong_FromUnsignedLong(x);
+	else
+		return PyInt_FromLong((long)x);
+}
+
+static PyObject *
+lu_longlong(const char *p, const formatdef *f)
+{
+	return _PyLong_FromByteArray((const unsigned char *)p,
+				      8,
+				      1, /* little-endian */
+				      1  /* signed */);
+}
+
+static PyObject *
+lu_ulonglong(const char *p, const formatdef *f)
+{
+	return _PyLong_FromByteArray((const unsigned char *)p,
+				      8,
+				      1, /* little-endian */
+				      0  /* signed */);
+}
+
+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;
+	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;
+	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,		lu_int,		lp_int},
+	{'B',	1,		0,		lu_uint,	lp_int},
+	{'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, numcodes, num, itemsize, x;
+
+	fmt = PyString_AS_STRING(self->s_format);
+
+	f = whichtable((char **)&fmt);
+	
+	s = fmt;
+	size = 0;
+	len = 0;
+	numcodes = 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;
+		}
+		if (c != 'x') numcodes++;
+
+		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((numcodes + 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 != 'x') {
+			codes->offset = size;
+			codes->repeat = num;
+			codes->fmtdef = e;
+			codes++;
+		}
+		size += num * e->size;
+	}
+	codes->fmtdef = NULL;
+	codes->offset = -1;
+	codes->repeat = -1;
+	
+	return 0;
+}
+
+static PyObject *
+s_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
+{
+	PyObject *self;
+	static PyObject *not_yet_string;
+
+	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)
+{
+	int sts = 0;
+	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);
+}
+
+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;
+	PyObject *result;
+	char *restart;
+	formatcode *code;
+	Py_ssize_t i;
+	
+	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;
+	}
+	result = PyTuple_New(soself->s_len);
+	if (result == NULL)
+		return NULL;
+	
+
+	restart = PyString_AS_STRING(inputstr);
+	i = 0;
+	for (code = soself->s_codes; code->fmtdef != NULL; code++) {
+		Py_ssize_t n;
+		PyObject *v;
+		const formatdef *e = code->fmtdef;
+		const char *res = restart + code->offset;
+		if (e->format == 's') {
+			v = PyString_FromStringAndSize(res, code->repeat);
+			if (v == NULL)
+				goto fail;
+			PyTuple_SET_ITEM(result, i++, v);
+		} else if (e->format == 'p') {
+			n = *(unsigned char*)res;
+			if (n >= code->repeat)
+				n = code->repeat - 1;
+			v = PyString_FromStringAndSize(res + 1, n);
+			if (v == NULL)
+				goto fail;
+			PyTuple_SET_ITEM(result, i++, v);
+		} else {
+			for (n = 0; n < code->repeat; n++) {
+				v = e->unpack(res, e);
+				if (v == NULL)
+					goto fail;
+				PyTuple_SET_ITEM(result, i++, v);
+				res += e->size;
+			}
+		}
+	}
+
+	return result;
+fail:
+	Py_DECREF(result);
+	return NULL;
+};
+
+
+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;
+	char *restart;
+	formatcode *code;
+	Py_ssize_t i;
+	
+	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;
+	}
+	
+	result = PyString_FromStringAndSize((char *)NULL, soself->s_size);
+	if (result == NULL)
+		return NULL;
+	
+	restart = PyString_AS_STRING(result);
+	memset(restart, '\0', soself->s_size);
+	i = 0;
+	for (code = soself->s_codes; code->fmtdef != NULL; code++) {
+		Py_ssize_t n;
+		PyObject *v;
+		const formatdef *e = code->fmtdef;
+		char *res = restart + 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");
+				goto fail;
+			}
+			n = PyString_GET_SIZE(v);
+			if (n > code->repeat)
+				n = code->repeat;
+			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");
+				goto fail;
+			}
+			n = PyString_GET_SIZE(v);
+			if (n > (code->repeat - 1))
+				n = code->repeat - 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 {
+			for (n = 0; n < code->repeat; n++) {
+				v = PyTuple_GET_ITEM(args, i++);
+				if (e->pack(res, v, e) < 0)
+					goto fail;
+				res += e->size;
+			}
+		}
+	}
+	
+	return result;
+
+fail:
+	Py_DECREF(result);
+	return NULL;
+	
+}
+
+
+/* List of functions */
+
+static struct PyMethodDef s_methods[] = {
+	{"pack",	s_pack,		METH_VARARGS, s_pack__doc__},
+	{"unpack",	s_unpack,	METH_O, s_unpack__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(&PyType_Type)
+	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;
+
+	/* 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);
+}