summaryrefslogtreecommitdiffstats
path: root/Modules/structmodule.c
blob: 9d1c436494c62e0a5b92d5c78e67f6d4c4ca16e0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267

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

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

static char struct__doc__[] = "\
Functions to convert between Python values and C structs.\n\
Python strings are used to hold the data representing the C struct\n\
and also as format strings to describe the layout of data in the C struct.\n\
\n\
The optional first format char indicates byte ordering and alignment:\n\
 @: native w/native alignment(default)\n\
 =: native w/standard alignment\n\
 <: little-endian, std. alignment\n\
 >: big-endian, std. alignment\n\
 !: network, std (same as >)\n\
\n\
The remaining chars indicate types of args and must match exactly;\n\
these can be preceded by a decimal repeat count:\n\
 x: pad byte (no data); c:char; b:signed byte; B:unsigned byte;\n\
 h:short; H:unsigned short; i:int; I:unsigned int;\n\
 l:long; L:unsigned long; f:float; d:double.\n\
Special cases (preceding decimal count indicates length):\n\
 s:string (array of char); p: pascal string (w. count byte).\n\
Special case (only available in native format):\n\
 P:an integer type that is wide enough to hold a pointer.\n\
Whitespace between formats is ignored.\n\
\n\
The variable struct.error is an exception raised on errors.";

#include "Python.h"

#include <ctype.h>


/* Exception */

static PyObject *StructError;


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

#ifdef __MWERKS__
/*
** XXXX We have a problem here. There are no unique alignment rules
** on the PowerPC mac. 
*/
#ifdef __powerc
#pragma options align=mac68k
#endif
#endif /* __MWERKS__ */

typedef struct { char c; short x; } s_short;
typedef struct { char c; int x; } s_int;
typedef struct { char c; long x; } s_long;
typedef struct { char c; float x; } s_float;
typedef struct { char c; double x; } s_double;
typedef struct { char c; void *x; } s_void_p;

#define SHORT_ALIGN (sizeof(s_short) - sizeof(short))
#define INT_ALIGN (sizeof(s_int) - sizeof(int))
#define LONG_ALIGN (sizeof(s_long) - sizeof(long))
#define FLOAT_ALIGN (sizeof(s_float) - sizeof(float))
#define DOUBLE_ALIGN (sizeof(s_double) - sizeof(double))
#define VOID_P_ALIGN (sizeof(s_void_p) - sizeof(void *))

#define STRINGIFY(x)    #x

#ifdef __powerc
#pragma options align=reset
#endif

/* 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);
	}
}


/* Floating point helpers */

/* These use ANSI/IEEE Standard 754-1985 (Standard for Binary Floating
   Point Arithmetic).  See the following URL:
   http://www.psc.edu/general/software/packages/ieee/ieee.html */

/* XXX Inf/NaN are not handled quite right (but underflow is!) */

static int
pack_float(double x, /* The number to pack */
           char *p,  /* Where to pack the high order byte */
           int incr) /* 1 for big-endian; -1 for little-endian */
{
	int s;
	int e;
	double f;
	long fbits;

	if (x < 0) {
		s = 1;
		x = -x;
	}
	else
		s = 0;

	f = frexp(x, &e);

	/* Normalize f to be in the range [1.0, 2.0) */
	if (0.5 <= f && f < 1.0) {
		f *= 2.0;
		e--;
	}
	else if (f == 0.0) {
		e = 0;
	}
	else {
		PyErr_SetString(PyExc_SystemError,
				"frexp() result out of range");
		return -1;
	}

	if (e >= 128) {
		/* XXX 128 itself is reserved for Inf/NaN */
		PyErr_SetString(PyExc_OverflowError,
				"float too large to pack with f format");
		return -1;
	}
	else if (e < -126) {
		/* Gradual underflow */
		f = ldexp(f, 126 + e);
		e = 0;
	}
	else if (!(e == 0 && f == 0.0)) {
		e += 127;
		f -= 1.0; /* Get rid of leading 1 */
	}

	f *= 8388608.0; /* 2**23 */
	fbits = (long) floor(f + 0.5); /* Round */

	/* First byte */
	*p = (s<<7) | (e>>1);
	p += incr;

	/* Second byte */
	*p = (char) (((e&1)<<7) | (fbits>>16));
	p += incr;

	/* Third byte */
	*p = (fbits>>8) & 0xFF;
	p += incr;

	/* Fourth byte */
	*p = fbits&0xFF;

	/* Done */
	return 0;
}

static int
pack_double(double x, /* The number to pack */
            char *p,  /* Where to pack the high order byte */
            int incr) /* 1 for big-endian; -1 for little-endian */
{
	int s;
	int e;
	double f;
	long fhi, flo;

	if (x < 0) {
		s = 1;
		x = -x;
	}
	else
		s = 0;

	f = frexp(x, &e);

	/* Normalize f to be in the range [1.0, 2.0) */
	if (0.5 <= f && f < 1.0) {
		f *= 2.0;
		e--;
	}
	else if (f == 0.0) {
		e = 0;
	}
	else {
		PyErr_SetString(PyExc_SystemError,
				"frexp() result out of range");
		return -1;
	}

	if (e >= 1024) {
		/* XXX 1024 itself is reserved for Inf/NaN */
		PyErr_SetString(PyExc_OverflowError,
				"float too large to pack with d format");
		return -1;
	}
	else if (e < -1022) {
		/* Gradual underflow */
		f = ldexp(f, 1022 + e);
		e = 0;
	}
	else if (!(e == 0 && f == 0.0)) {
		e += 1023;
		f -= 1.0; /* Get rid of leading 1 */
	}

	/* fhi receives the high 28 bits; flo the low 24 bits (== 52 bits) */
	f *= 268435456.0; /* 2**28 */
	fhi = (long) floor(f); /* Truncate */
	f -= (double)fhi;
	f *= 16777216.0; /* 2**24 */
	flo = (long) floor(f + 0.5); /* Round */

	/* First byte */
	*p = (s<<7) | (e>>4);
	p += incr;

	/* Second byte */
	*p = (char) (((e&0xF)<<4) | (fhi>>24));
	p += incr;

	/* Third byte */
	*p = (fhi>>16) & 0xFF;
	p += incr;

	/* Fourth byte */
	*p = (fhi>>8) & 0xFF;
	p += incr;

	/* Fifth byte */
	*p = fhi & 0xFF;
	p += incr;

	/* Sixth byte */
	*p = (flo>>16) & 0xFF;
	p += incr;

	/* Seventh byte */
	*p = (flo>>8) & 0xFF;
	p += incr;

	/* Eighth byte */
	*p = flo & 0xFF;
	p += incr;

	/* Done */
	return 0;
}

static PyObject *
unpack_float(const char *p,  /* Where the high order byte is */
             int incr)       /* 1 for big-endian; -1 for little-endian */
{
	int s;
	int e;
	long f;
	double x;

	/* First byte */
	s = (*p>>7) & 1;
	e = (*p & 0x7F) << 1;
	p += incr;

	/* Second byte */
	e |= (*p>>7) & 1;
	f = (*p & 0x7F) << 16;
	p += incr;

	/* Third byte */
	f |= (*p & 0xFF) << 8;
	p += incr;

	/* Fourth byte */
	f |= *p & 0xFF;

	x = (double)f / 8388608.0;

	/* XXX This sadly ignores Inf/NaN issues */
	if (e == 0)
		e = -126;
	else {
		x += 1.0;
		e -= 127;
	}
	x = ldexp(x, e);

	if (s)
		x = -x;

	return PyFloat_FromDouble(x);
}

static PyObject *
unpack_double(const char *p,  /* Where the high order byte is */
              int incr)       /* 1 for big-endian; -1 for little-endian */
{
	int s;
	int e;
	long fhi, flo;
	double x;

	/* First byte */
	s = (*p>>7) & 1;
	e = (*p & 0x7F) << 4;
	p += incr;

	/* Second byte */
	e |= (*p>>4) & 0xF;
	fhi = (*p & 0xF) << 24;
	p += incr;

	/* Third byte */
	fhi |= (*p & 0xFF) << 16;
	p += incr;

	/* Fourth byte */
	fhi |= (*p & 0xFF) << 8;
	p += incr;

	/* Fifth byte */
	fhi |= *p & 0xFF;
	p += incr;

	/* Sixth byte */
	flo = (*p & 0xFF) << 16;
	p += incr;

	/* Seventh byte */
	flo |= (*p & 0xFF) << 8;
	p += incr;

	/* Eighth byte */
	flo |= *p & 0xFF;
	p += incr;

	x = (double)fhi + (double)flo / 16777216.0; /* 2**24 */
	x /= 268435456.0; /* 2**28 */

	/* XXX This sadly ignores Inf/NaN */
	if (e == 0)
		e = -1022;
	else {
		x += 1.0;
		e -= 1023;
	}
	x = ldexp(x, e);

	if (s)
		x = -x;

	return PyFloat_FromDouble(x);
}


/* 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;

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)
{
	return PyInt_FromLong((long) *(short *)p);
}

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

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

static PyObject *
nu_uint(const char *p, const formatdef *f)
{
	unsigned int x = *(unsigned int *)p;
	return PyLong_FromUnsignedLong((unsigned long)x);
}

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

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

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

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

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

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;
	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;
	}
	* (short *)p = (short)x;
	return 0;
}

static int
np_ushort(char *p, PyObject *v, const formatdef *f)
{
	long x;
	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;
	}
	* (unsigned short *)p = (unsigned short)x;
	return 0;
}

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

static int
np_uint(char *p, PyObject *v, const formatdef *f)
{
	unsigned long x;
	if (get_ulong(v, &x) < 0)
		return -1;
	* (unsigned int *)p = x;
	return 0;
}

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

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(float));
	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 = PyLong_AsVoidPtr(v);
	if (x == NULL && PyErr_Occurred()) {
		/* ### hrm. PyLong_AsVoidPtr raises SystemError */
		if (PyErr_ExceptionMatches(PyExc_TypeError))
			PyErr_SetString(StructError,
					"required argument is not an integer");
		return -1;
	}
	*(void **)p = 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},
	{0}
};

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_float(const char *p, const formatdef *f)
{
	return unpack_float(p, 1);
}

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

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_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 pack_float(x, p, 1);
}

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 pack_double(x, p, 1);
}

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},
	{'f',	4,		0,		bu_float,	bp_float},
	{'d',	8,		0,		bu_double,	bp_double},
	{0}
};

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_float(const char *p, const formatdef *f)
{
	return unpack_float(p+3, -1);
}

static PyObject *
lu_double(const char *p, const formatdef *f)
{
	return unpack_double(p+7, -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_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 pack_float(x, p+3, -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 pack_double(x, p+7, -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},
	{'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
calcsize(const char *fmt, const formatdef *f)
{
	const formatdef *e;
	const char *s;
	char c;
	int size,  num, itemsize, x;

	s = fmt;
	size = 0;
	while ((c = *s++) != '\0') {
		if (isspace((int)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;
		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;
		}
	}

	return size;
}


static char calcsize__doc__[] = "\
calcsize(fmt) -> int\n\
Return size of C struct described by format string fmt.\n\
See struct.__doc__ for more on format strings.";

static PyObject *
struct_calcsize(PyObject *self, PyObject *args)
{
	char *fmt;
	const formatdef *f;
	int size;

	if (!PyArg_ParseTuple(args, "s:calcsize", &fmt))
		return NULL;
	f = whichtable(&fmt);
	size = calcsize(fmt, f);
	if (size < 0)
		return NULL;
	return PyInt_FromLong((long)size);
}


static char pack__doc__[] = "\
pack(fmt, v1, v2, ...) -> string\n\
Return string containing values v1, v2, ... packed according to fmt.\n\
See struct.__doc__ for more on format strings.";

static PyObject *
struct_pack(PyObject *self, PyObject *args)
{
	const formatdef *f, *e;
	PyObject *format, *result, *v;
	char *fmt;
	int size, num;
	int i, n;
	char *s, *res, *restart, *nres;
	char c;

	if (args == NULL || !PyTuple_Check(args) ||
	    (n = PyTuple_Size(args)) < 1)
        {
		PyErr_SetString(PyExc_TypeError, 
			"struct.pack requires at least one argument");
		return NULL;
	}
	format = PyTuple_GetItem(args, 0);
	if (!PyArg_Parse(format, "s", &fmt))
		return NULL;
	f = whichtable(&fmt);
	size = calcsize(fmt, f);
	if (size < 0)
		return NULL;
	result = PyString_FromStringAndSize((char *)NULL, size);
	if (result == NULL)
		return NULL;

	s = fmt;
	i = 1;
	res = restart = PyString_AsString(result);

	while ((c = *s++) != '\0') {
		if (isspace((int)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);
		if (e == NULL)
			goto fail;
		nres = restart + align((int)(res-restart), c, e);
		/* Fill padd bytes with zeros */
		while (res < nres)
			*res++ = '\0';
		if (num == 0 && c != 's')
			continue;
		do {
			if (c == 'x') {
				/* doesn't consume arguments */
				memset(res, '\0', num);
				res += num;
				break;
			}
			if (i >= n) {
				PyErr_SetString(StructError,
					"insufficient arguments to pack");
				goto fail;
				}
			v = PyTuple_GetItem(args, i++);
			if (v == NULL)
				goto fail;
			if (c == 's') {
				/* num is string size, not repeat count */
				int n;
				if (!PyString_Check(v)) {
					PyErr_SetString(StructError,
					  "argument for 's' must be a string");
					goto fail;
				}
				n = PyString_Size(v);
				if (n > num)
					n = num;
				if (n > 0)
					memcpy(res, PyString_AsString(v), n);
				if (n < num)
					memset(res+n, '\0', num-n);
				res += num;
				break;
			}
			else if (c == 'p') {
				/* num is string size + 1,
				   to fit in the count byte */
				int n;
				num--; /* now num is max string size */
				if (!PyString_Check(v)) {
					PyErr_SetString(StructError,
					  "argument for 'p' must be a string");
					goto fail;
				}
				n = PyString_Size(v);
				if (n > num)
					n = num;
				if (n > 0)
					memcpy(res+1, PyString_AsString(v), n);
				if (n < num)
					/* no real need, just to be nice */
					memset(res+1+n, '\0', num-n);
				*res++ = n; /* store the length byte */
				res += num;
				break;
			}
			else {
				if (e->pack(res, v, e) < 0)
					goto fail;
				res += e->size;
			}
		} while (--num > 0);
	}

	if (i < n) {
		PyErr_SetString(StructError,
				"too many arguments for pack format");
		goto fail;
	}

	return result;

 fail:
	Py_DECREF(result);
	return NULL;
}


static char unpack__doc__[] = "\
unpack(fmt, string) -> (v1, v2, ...)\n\
Unpack the string, containing packed C structure data, according\n\
to fmt.  Requires len(string)==calcsize(fmt).\n\
See struct.__doc__ for more on format strings.";

static PyObject *
struct_unpack(PyObject *self, PyObject *args)
{
	const formatdef *f, *e;
	char *str, *start, *fmt, *s;
	char c;
	int len, size, num;
	PyObject *res, *v;

	if (!PyArg_ParseTuple(args, "ss#:unpack", &fmt, &start, &len))
		return NULL;
	f = whichtable(&fmt);
	size = calcsize(fmt, f);
	if (size < 0)
		return NULL;
	if (size != len) {
		PyErr_SetString(StructError,
				"unpack str size does not match format");
		return NULL;
	}
	res = PyList_New(0);
	if (res == NULL)
		return NULL;
	str = start;
	s = fmt;
	while ((c = *s++) != '\0') {
		if (isspace((int)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);
		if (e == NULL)
			goto fail;
		str = start + align((int)(str-start), c, e);
		if (num == 0 && c != 's')
			continue;

		do {
			if (c == 'x') {
				str += num;
				break;
			}
			if (c == 's') {
				/* num is string size, not repeat count */
				v = PyString_FromStringAndSize(str, num);
				if (v == NULL)
					goto fail;
				str += num;
				num = 0;
			}
			else if (c == 'p') {
				/* num is string buffer size,
				   not repeat count */
				int n = *(unsigned char*)str;
				/* first byte (unsigned) is string size */
				if (n >= num)
					n = num-1;
				v = PyString_FromStringAndSize(str+1, n);
				if (v == NULL)
					goto fail;
				str += num;
				num = 0;
			}
			else {
				v = e->unpack(str, e);
				if (v == NULL)
					goto fail;
				str += e->size;
			}
			if (v == NULL || PyList_Append(res, v) < 0)
				goto fail;
			Py_DECREF(v);
		} while (--num > 0);
	}

	v = PyList_AsTuple(res);
	Py_DECREF(res);
	return v;

 fail:
	Py_DECREF(res);
	return NULL;
}


/* List of functions */

static PyMethodDef struct_methods[] = {
	{"calcsize",	struct_calcsize,	METH_VARARGS, calcsize__doc__},
	{"pack",	struct_pack,		METH_VARARGS, pack__doc__},
	{"unpack",	struct_unpack,		METH_VARARGS, unpack__doc__},
	{NULL,		NULL}		/* sentinel */
};


/* Module initialization */

DL_EXPORT(void)
initstruct(void)
{
	PyObject *m, *d;

	/* Create the module and add the functions */
	m = Py_InitModule4("struct", struct_methods, struct__doc__,
			   (PyObject*)NULL, PYTHON_API_VERSION);

	/* Add some symbolic constants to the module */
	d = PyModule_GetDict(m);
	StructError = PyErr_NewException("struct.error", NULL, NULL);
	if (StructError == NULL)
		return;
	PyDict_SetItemString(d, "error", StructError);
}