aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/tools/python/src/Python/pystrtod.c
blob: 29d79960ab92226b0a21ec959771ae342caec9f8 (plain) (blame)
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
/* -*- Mode: C; c-file-style: "python" -*- */

#include <Python.h>
#include <locale.h>

/* Case-insensitive string match used for nan and inf detection; t should be
   lower-case.  Returns 1 for a successful match, 0 otherwise. */

static int
case_insensitive_match(const char *s, const char *t)
{
    while(*t && Py_TOLOWER(*s) == *t) {
        s++;
        t++;
    }
    return *t ? 0 : 1;
}

/* _Py_parse_inf_or_nan: Attempt to parse a string of the form "nan", "inf" or
   "infinity", with an optional leading sign of "+" or "-".  On success,
   return the NaN or Infinity as a double and set *endptr to point just beyond
   the successfully parsed portion of the string.  On failure, return -1.0 and
   set *endptr to point to the start of the string. */

double
_Py_parse_inf_or_nan(const char *p, char **endptr)
{
    double retval;
    const char *s;
    int negate = 0;

    s = p;
    if (*s == '-') {
        negate = 1;
        s++;
    }
    else if (*s == '+') {
        s++;
    }
    if (case_insensitive_match(s, "inf")) {
        s += 3;
        if (case_insensitive_match(s, "inity"))
            s += 5;
        retval = negate ? -Py_HUGE_VAL : Py_HUGE_VAL;
    }
#ifdef Py_NAN
    else if (case_insensitive_match(s, "nan")) {
        s += 3;
        retval = negate ? -Py_NAN : Py_NAN;
    }
#endif
    else {
        s = p;
        retval = -1.0;
    }
    *endptr = (char *)s;
    return retval;
}

/**
 * PyOS_ascii_strtod:
 * @nptr:    the string to convert to a numeric value.
 * @endptr:  if non-%NULL, it returns the character after
 *           the last character used in the conversion.
 *
 * Converts a string to a #gdouble value.
 * This function behaves like the standard strtod() function
 * does in the C locale. It does this without actually
 * changing the current locale, since that would not be
 * thread-safe.
 *
 * This function is typically used when reading configuration
 * files or other non-user input that should be locale independent.
 * To handle input from the user you should normally use the
 * locale-sensitive system strtod() function.
 *
 * If the correct value would cause overflow, plus or minus %HUGE_VAL
 * is returned (according to the sign of the value), and %ERANGE is
 * stored in %errno. If the correct value would cause underflow,
 * zero is returned and %ERANGE is stored in %errno.
 * If memory allocation fails, %ENOMEM is stored in %errno.
 *
 * This function resets %errno before calling strtod() so that
 * you can reliably detect overflow and underflow.
 *
 * Return value: the #gdouble value.
 **/

#ifndef PY_NO_SHORT_FLOAT_REPR

double
_PyOS_ascii_strtod(const char *nptr, char **endptr)
{
    double result;
    _Py_SET_53BIT_PRECISION_HEADER;

    assert(nptr != NULL);
    /* Set errno to zero, so that we can distinguish zero results
       and underflows */
    errno = 0;

    _Py_SET_53BIT_PRECISION_START;
    result = _Py_dg_strtod(nptr, endptr);
    _Py_SET_53BIT_PRECISION_END;

    if (*endptr == nptr)
        /* string might represent an inf or nan */
        result = _Py_parse_inf_or_nan(nptr, endptr);

    return result;

}

#else

/*
   Use system strtod;  since strtod is locale aware, we may
   have to first fix the decimal separator.

   Note that unlike _Py_dg_strtod, the system strtod may not always give
   correctly rounded results.
*/

double
_PyOS_ascii_strtod(const char *nptr, char **endptr)
{
    char *fail_pos;
    double val = -1.0;
    struct lconv *locale_data;
    const char *decimal_point;
    size_t decimal_point_len;
    const char *p, *decimal_point_pos;
    const char *end = NULL; /* Silence gcc */
    const char *digits_pos = NULL;
    int negate = 0;

    assert(nptr != NULL);

    fail_pos = NULL;

    locale_data = localeconv();
    decimal_point = locale_data->decimal_point;
    decimal_point_len = strlen(decimal_point);

    assert(decimal_point_len != 0);

    decimal_point_pos = NULL;

    /* Parse infinities and nans */
    val = _Py_parse_inf_or_nan(nptr, endptr);
    if (*endptr != nptr)
        return val;

    /* Set errno to zero, so that we can distinguish zero results
       and underflows */
    errno = 0;

    /* We process the optional sign manually, then pass the remainder to
       the system strtod.  This ensures that the result of an underflow
       has the correct sign. (bug #1725)  */
    p = nptr;
    /* Process leading sign, if present */
    if (*p == '-') {
        negate = 1;
        p++;
    }
    else if (*p == '+') {
        p++;
    }

    /* Some platform strtods accept hex floats; Python shouldn't (at the
       moment), so we check explicitly for strings starting with '0x'. */
    if (*p == '0' && (*(p+1) == 'x' || *(p+1) == 'X'))
        goto invalid_string;

    /* Check that what's left begins with a digit or decimal point */
    if (!Py_ISDIGIT(*p) && *p != '.')
        goto invalid_string;

    digits_pos = p;
    if (decimal_point[0] != '.' ||
        decimal_point[1] != 0)
    {
        /* Look for a '.' in the input; if present, it'll need to be
           swapped for the current locale's decimal point before we
           call strtod.  On the other hand, if we find the current
           locale's decimal point then the input is invalid. */
        while (Py_ISDIGIT(*p))
            p++;

        if (*p == '.')
        {
            decimal_point_pos = p++;

            /* locate end of number */
            while (Py_ISDIGIT(*p))
                p++;

            if (*p == 'e' || *p == 'E')
                p++;
            if (*p == '+' || *p == '-')
                p++;
            while (Py_ISDIGIT(*p))
                p++;
            end = p;
        }
        else if (strncmp(p, decimal_point, decimal_point_len) == 0)
            /* Python bug #1417699 */
            goto invalid_string;
        /* For the other cases, we need not convert the decimal
           point */
    }

    if (decimal_point_pos) {
        char *copy, *c;
        /* Create a copy of the input, with the '.' converted to the
           locale-specific decimal point */
        copy = (char *)PyMem_MALLOC(end - digits_pos +
                                    1 + decimal_point_len);
        if (copy == NULL) {
            *endptr = (char *)nptr;
            errno = ENOMEM;
            return val;
        }

        c = copy;
        memcpy(c, digits_pos, decimal_point_pos - digits_pos);
        c += decimal_point_pos - digits_pos;
        memcpy(c, decimal_point, decimal_point_len);
        c += decimal_point_len;
        memcpy(c, decimal_point_pos + 1,
               end - (decimal_point_pos + 1));
        c += end - (decimal_point_pos + 1);
        *c = 0;

        val = strtod(copy, &fail_pos);

        if (fail_pos)
        {
            if (fail_pos > decimal_point_pos)
                fail_pos = (char *)digits_pos +
                    (fail_pos - copy) -
                    (decimal_point_len - 1);
            else
                fail_pos = (char *)digits_pos +
                    (fail_pos - copy);
        }

        PyMem_FREE(copy);

    }
    else {
        val = strtod(digits_pos, &fail_pos);
    }

    if (fail_pos == digits_pos)
        goto invalid_string;

    if (negate && fail_pos != nptr)
        val = -val;
    *endptr = fail_pos;

    return val;

  invalid_string:
    *endptr = (char*)nptr;
    errno = EINVAL;
    return -1.0;
}

#endif

/* PyOS_ascii_strtod is DEPRECATED in Python 2.7 and 3.1 */

double
PyOS_ascii_strtod(const char *nptr, char **endptr)
{
    char *fail_pos;
    const char *p;
    double x;

    if (PyErr_WarnEx(PyExc_DeprecationWarning,
                     "PyOS_ascii_strtod and PyOS_ascii_atof are "
                     "deprecated.  Use PyOS_string_to_double "
                     "instead.", 1) < 0)
        return -1.0;

    /* _PyOS_ascii_strtod already does everything that we want,
       except that it doesn't parse leading whitespace */
    p = nptr;
    while (Py_ISSPACE(*p))
        p++;
    x = _PyOS_ascii_strtod(p, &fail_pos);
    if (fail_pos == p)
        fail_pos = (char *)nptr;
    if (endptr)
        *endptr = (char *)fail_pos;
    return x;
}

/* PyOS_ascii_strtod is DEPRECATED in Python 2.7 and 3.1 */

double
PyOS_ascii_atof(const char *nptr)
{
    return PyOS_ascii_strtod(nptr, NULL);
}

/* PyOS_string_to_double is the recommended replacement for the deprecated
   PyOS_ascii_strtod and PyOS_ascii_atof functions.  It converts a
   null-terminated byte string s (interpreted as a string of ASCII characters)
   to a float.  The string should not have leading or trailing whitespace (in
   contrast, PyOS_ascii_strtod allows leading whitespace but not trailing
   whitespace).  The conversion is independent of the current locale.

   If endptr is NULL, try to convert the whole string.  Raise ValueError and
   return -1.0 if the string is not a valid representation of a floating-point
   number.

   If endptr is non-NULL, try to convert as much of the string as possible.
   If no initial segment of the string is the valid representation of a
   floating-point number then *endptr is set to point to the beginning of the
   string, -1.0 is returned and again ValueError is raised.

   On overflow (e.g., when trying to convert '1e500' on an IEEE 754 machine),
   if overflow_exception is NULL then +-Py_HUGE_VAL is returned, and no Python
   exception is raised.  Otherwise, overflow_exception should point to
   a Python exception, this exception will be raised, -1.0 will be returned,
   and *endptr will point just past the end of the converted value.

   If any other failure occurs (for example lack of memory), -1.0 is returned
   and the appropriate Python exception will have been set.
*/

double
PyOS_string_to_double(const char *s,
                      char **endptr,
                      PyObject *overflow_exception)
{
    double x, result=-1.0;
    char *fail_pos;

    errno = 0;
    PyFPE_START_PROTECT("PyOS_string_to_double", return -1.0)
    x = _PyOS_ascii_strtod(s, &fail_pos);
    PyFPE_END_PROTECT(x)

    if (errno == ENOMEM) {
        PyErr_NoMemory();
        fail_pos = (char *)s;
    }
    else if (!endptr && (fail_pos == s || *fail_pos != '\0'))
        PyErr_Format(PyExc_ValueError,
                      "could not convert string to float: "
                      "%.200s", s);
    else if (fail_pos == s)
        PyErr_Format(PyExc_ValueError,
                      "could not convert string to float: "
                      "%.200s", s);
    else if (errno == ERANGE && fabs(x) >= 1.0 && overflow_exception)
        PyErr_Format(overflow_exception,
                      "value too large to convert to float: "
                      "%.200s", s);
    else
        result = x;

    if (endptr != NULL)
        *endptr = fail_pos;
    return result;
}

/* Given a string that may have a decimal point in the current
   locale, change it back to a dot.  Since the string cannot get
   longer, no need for a maximum buffer size parameter. */
Py_LOCAL_INLINE(void)
change_decimal_from_locale_to_dot(char* buffer)
{
    struct lconv *locale_data = localeconv();
    const char *decimal_point = locale_data->decimal_point;

    if (decimal_point[0] != '.' || decimal_point[1] != 0) {
        size_t decimal_point_len = strlen(decimal_point);

        if (*buffer == '+' || *buffer == '-')
            buffer++;
        while (Py_ISDIGIT(*buffer))
            buffer++;
        if (strncmp(buffer, decimal_point, decimal_point_len) == 0) {
            *buffer = '.';
            buffer++;
            if (decimal_point_len > 1) {
                /* buffer needs to get smaller */
                size_t rest_len = strlen(buffer +
                                     (decimal_point_len - 1));
                memmove(buffer,
                    buffer + (decimal_point_len - 1),
                    rest_len);
                buffer[rest_len] = 0;
            }
        }
    }
}


/* From the C99 standard, section 7.19.6:
The exponent always contains at least two digits, and only as many more digits
as necessary to represent the exponent.
*/
#define MIN_EXPONENT_DIGITS 2

/* Ensure that any exponent, if present, is at least MIN_EXPONENT_DIGITS
   in length. */
Py_LOCAL_INLINE(void)
ensure_minimum_exponent_length(char* buffer, size_t buf_size)
{
    char *p = strpbrk(buffer, "eE");
    if (p && (*(p + 1) == '-' || *(p + 1) == '+')) {
        char *start = p + 2;
        int exponent_digit_cnt = 0;
        int leading_zero_cnt = 0;
        int in_leading_zeros = 1;
        int significant_digit_cnt;

        /* Skip over the exponent and the sign. */
        p += 2;

        /* Find the end of the exponent, keeping track of leading
           zeros. */
        while (*p && Py_ISDIGIT(*p)) {
            if (in_leading_zeros && *p == '0')
                ++leading_zero_cnt;
            if (*p != '0')
                in_leading_zeros = 0;
            ++p;
            ++exponent_digit_cnt;
        }

        significant_digit_cnt = exponent_digit_cnt - leading_zero_cnt;
        if (exponent_digit_cnt == MIN_EXPONENT_DIGITS) {
            /* If there are 2 exactly digits, we're done,
               regardless of what they contain */
        }
        else if (exponent_digit_cnt > MIN_EXPONENT_DIGITS) {
            int extra_zeros_cnt;

            /* There are more than 2 digits in the exponent.  See
               if we can delete some of the leading zeros */
            if (significant_digit_cnt < MIN_EXPONENT_DIGITS)
                significant_digit_cnt = MIN_EXPONENT_DIGITS;
            extra_zeros_cnt = exponent_digit_cnt -
                significant_digit_cnt;

            /* Delete extra_zeros_cnt worth of characters from the
               front of the exponent */
            assert(extra_zeros_cnt >= 0);

            /* Add one to significant_digit_cnt to copy the
               trailing 0 byte, thus setting the length */
            memmove(start,
                start + extra_zeros_cnt,
                significant_digit_cnt + 1);
        }
        else {
            /* If there are fewer than 2 digits, add zeros
               until there are 2, if there's enough room */
            int zeros = MIN_EXPONENT_DIGITS - exponent_digit_cnt;
            if (start + zeros + exponent_digit_cnt + 1
                  < buffer + buf_size) {
                memmove(start + zeros, start,
                    exponent_digit_cnt + 1);
                memset(start, '0', zeros);
            }
        }
    }
}

/* Remove trailing zeros after the decimal point from a numeric string; also
   remove the decimal point if all digits following it are zero.  The numeric
   string must end in '\0', and should not have any leading or trailing
   whitespace.  Assumes that the decimal point is '.'. */
Py_LOCAL_INLINE(void)
remove_trailing_zeros(char *buffer)
{
    char *old_fraction_end, *new_fraction_end, *end, *p;

    p = buffer;
    if (*p == '-' || *p == '+')
        /* Skip leading sign, if present */
        ++p;
    while (Py_ISDIGIT(*p))
        ++p;

    /* if there's no decimal point there's nothing to do */
    if (*p++ != '.')
        return;

    /* scan any digits after the point */
    while (Py_ISDIGIT(*p))
        ++p;
    old_fraction_end = p;

    /* scan up to ending '\0' */
    while (*p != '\0')
        p++;
    /* +1 to make sure that we move the null byte as well */
    end = p+1;

    /* scan back from fraction_end, looking for removable zeros */
    p = old_fraction_end;
    while (*(p-1) == '0')
        --p;
    /* and remove point if we've got that far */
    if (*(p-1) == '.')
        --p;
    new_fraction_end = p;

    memmove(new_fraction_end, old_fraction_end, end-old_fraction_end);
}

/* Ensure that buffer has a decimal point in it.  The decimal point will not
   be in the current locale, it will always be '.'. Don't add a decimal point
   if an exponent is present.  Also, convert to exponential notation where
   adding a '.0' would produce too many significant digits (see issue 5864).

   Returns a pointer to the fixed buffer, or NULL on failure.
*/
Py_LOCAL_INLINE(char *)
ensure_decimal_point(char* buffer, size_t buf_size, int precision)
{
    int digit_count, insert_count = 0, convert_to_exp = 0;
    char *chars_to_insert, *digits_start;

    /* search for the first non-digit character */
    char *p = buffer;
    if (*p == '-' || *p == '+')
        /* Skip leading sign, if present.  I think this could only
           ever be '-', but it can't hurt to check for both. */
        ++p;
    digits_start = p;
    while (*p && Py_ISDIGIT(*p))
        ++p;
    digit_count = Py_SAFE_DOWNCAST(p - digits_start, Py_ssize_t, int);

    if (*p == '.') {
        if (Py_ISDIGIT(*(p+1))) {
            /* Nothing to do, we already have a decimal
               point and a digit after it */
        }
        else {
            /* We have a decimal point, but no following
               digit.  Insert a zero after the decimal. */
            /* can't ever get here via PyOS_double_to_string */
            assert(precision == -1);
            ++p;
            chars_to_insert = "0";
            insert_count = 1;
        }
    }
    else if (!(*p == 'e' || *p == 'E')) {
        /* Don't add ".0" if we have an exponent. */
        if (digit_count == precision) {
            /* issue 5864: don't add a trailing .0 in the case
               where the '%g'-formatted result already has as many
               significant digits as were requested.  Switch to
               exponential notation instead. */
            convert_to_exp = 1;
            /* no exponent, no point, and we shouldn't land here
               for infs and nans, so we must be at the end of the
               string. */
            assert(*p == '\0');
        }
        else {
            assert(precision == -1 || digit_count < precision);
            chars_to_insert = ".0";
            insert_count = 2;
        }
    }
    if (insert_count) {
        size_t buf_len = strlen(buffer);
        if (buf_len + insert_count + 1 >= buf_size) {
            /* If there is not enough room in the buffer
               for the additional text, just skip it.  It's
               not worth generating an error over. */
        }
        else {
            memmove(p + insert_count, p,
                buffer + strlen(buffer) - p + 1);
            memcpy(p, chars_to_insert, insert_count);
        }
    }
    if (convert_to_exp) {
        int written;
        size_t buf_avail;
        p = digits_start;
        /* insert decimal point */
        assert(digit_count >= 1);
        memmove(p+2, p+1, digit_count); /* safe, but overwrites nul */
        p[1] = '.';
        p += digit_count+1;
        assert(p <= buf_size+buffer);
        buf_avail = buf_size+buffer-p;
        if (buf_avail == 0)
            return NULL;
        /* Add exponent.  It's okay to use lower case 'e': we only
           arrive here as a result of using the empty format code or
           repr/str builtins and those never want an upper case 'E' */
        written = PyOS_snprintf(p, buf_avail, "e%+.02d", digit_count-1);
        if (!(0 <= written &&
              written < Py_SAFE_DOWNCAST(buf_avail, size_t, int)))
            /* output truncated, or something else bad happened */
            return NULL;
        remove_trailing_zeros(buffer);
    }
    return buffer;
}

/* see FORMATBUFLEN in unicodeobject.c */
#define FLOAT_FORMATBUFLEN 120

/**
 * PyOS_ascii_formatd:
 * @buffer: A buffer to place the resulting string in
 * @buf_size: The length of the buffer.
 * @format: The printf()-style format to use for the
 *          code to use for converting.
 * @d: The #gdouble to convert
 *
 * Converts a #gdouble to a string, using the '.' as
 * decimal point. To format the number you pass in
 * a printf()-style format string. Allowed conversion
 * specifiers are 'e', 'E', 'f', 'F', 'g', 'G', and 'Z'.
 *
 * 'Z' is the same as 'g', except it always has a decimal and
 *     at least one digit after the decimal.
 *
 * Return value: The pointer to the buffer with the converted string.
 * On failure returns NULL but does not set any Python exception.
 **/
char *
_PyOS_ascii_formatd(char       *buffer,
                   size_t      buf_size,
                   const char *format,
                   double      d,
                   int         precision)
{
    char format_char;
    size_t format_len = strlen(format);

    /* Issue 2264: code 'Z' requires copying the format.  'Z' is 'g', but
       also with at least one character past the decimal. */
    char tmp_format[FLOAT_FORMATBUFLEN];

    /* The last character in the format string must be the format char */
    format_char = format[format_len - 1];

    if (format[0] != '%')
        return NULL;

    /* I'm not sure why this test is here.  It's ensuring that the format
       string after the first character doesn't have a single quote, a
       lowercase l, or a percent. This is the reverse of the commented-out
       test about 10 lines ago. */
    if (strpbrk(format + 1, "'l%"))
        return NULL;

    /* Also curious about this function is that it accepts format strings
       like "%xg", which are invalid for floats.  In general, the
       interface to this function is not very good, but changing it is
       difficult because it's a public API. */

    if (!(format_char == 'e' || format_char == 'E' ||
          format_char == 'f' || format_char == 'F' ||
          format_char == 'g' || format_char == 'G' ||
          format_char == 'Z'))
        return NULL;

    /* Map 'Z' format_char to 'g', by copying the format string and
       replacing the final char with a 'g' */
    if (format_char == 'Z') {
        if (format_len + 1 >= sizeof(tmp_format)) {
            /* The format won't fit in our copy.  Error out.  In
               practice, this will never happen and will be
               detected by returning NULL */
            return NULL;
        }
        strcpy(tmp_format, format);
        tmp_format[format_len - 1] = 'g';
        format = tmp_format;
    }


    /* Have PyOS_snprintf do the hard work */
    PyOS_snprintf(buffer, buf_size, format, d);

    /* Do various fixups on the return string */

    /* Get the current locale, and find the decimal point string.
       Convert that string back to a dot. */
    change_decimal_from_locale_to_dot(buffer);

    /* If an exponent exists, ensure that the exponent is at least
       MIN_EXPONENT_DIGITS digits, providing the buffer is large enough
       for the extra zeros.  Also, if there are more than
       MIN_EXPONENT_DIGITS, remove as many zeros as possible until we get
       back to MIN_EXPONENT_DIGITS */
    ensure_minimum_exponent_length(buffer, buf_size);

    /* If format_char is 'Z', make sure we have at least one character
       after the decimal point (and make sure we have a decimal point);
       also switch to exponential notation in some edge cases where the
       extra character would produce more significant digits that we
       really want. */
    if (format_char == 'Z')
        buffer = ensure_decimal_point(buffer, buf_size, precision);

    return buffer;
}

char *
PyOS_ascii_formatd(char       *buffer,
                   size_t      buf_size,
                   const char *format,
                   double      d)
{
    if (PyErr_WarnEx(PyExc_DeprecationWarning,
                     "PyOS_ascii_formatd is deprecated, "
                     "use PyOS_double_to_string instead", 1) < 0)
        return NULL;

    return _PyOS_ascii_formatd(buffer, buf_size, format, d, -1);
}

#ifdef PY_NO_SHORT_FLOAT_REPR

/* The fallback code to use if _Py_dg_dtoa is not available. */

PyAPI_FUNC(char *) PyOS_double_to_string(double val,
                                         char format_code,
                                         int precision,
                                         int flags,
                                         int *type)
{
    char format[32];
    Py_ssize_t bufsize;
    char *buf;
    int t, exp;
    int upper = 0;

    /* Validate format_code, and map upper and lower case */
    switch (format_code) {
    case 'e':          /* exponent */
    case 'f':          /* fixed */
    case 'g':          /* general */
        break;
    case 'E':
        upper = 1;
        format_code = 'e';
        break;
    case 'F':
        upper = 1;
        format_code = 'f';
        break;
    case 'G':
        upper = 1;
        format_code = 'g';
        break;
    case 'r':          /* repr format */
        /* Supplied precision is unused, must be 0. */
        if (precision != 0) {
            PyErr_BadInternalCall();
            return NULL;
        }
        /* The repr() precision (17 significant decimal digits) is the
           minimal number that is guaranteed to have enough precision
           so that if the number is read back in the exact same binary
           value is recreated.  This is true for IEEE floating point
           by design, and also happens to work for all other modern
           hardware. */
        precision = 17;
        format_code = 'g';
        break;
    default:
        PyErr_BadInternalCall();
        return NULL;
    }

    /* Here's a quick-and-dirty calculation to figure out how big a buffer
       we need.  In general, for a finite float we need:

         1 byte for each digit of the decimal significand, and

         1 for a possible sign
         1 for a possible decimal point
         2 for a possible [eE][+-]
         1 for each digit of the exponent;  if we allow 19 digits
           total then we're safe up to exponents of 2**63.
         1 for the trailing nul byte

       This gives a total of 24 + the number of digits in the significand,
       and the number of digits in the significand is:

         for 'g' format: at most precision, except possibly
           when precision == 0, when it's 1.
         for 'e' format: precision+1
         for 'f' format: precision digits after the point, at least 1
           before.  To figure out how many digits appear before the point
           we have to examine the size of the number.  If fabs(val) < 1.0
           then there will be only one digit before the point.  If
           fabs(val) >= 1.0, then there are at most

         1+floor(log10(ceiling(fabs(val))))

           digits before the point (where the 'ceiling' allows for the
           possibility that the rounding rounds the integer part of val
           up).  A safe upper bound for the above quantity is
           1+floor(exp/3), where exp is the unique integer such that 0.5
           <= fabs(val)/2**exp < 1.0.  This exp can be obtained from
           frexp.

       So we allow room for precision+1 digits for all formats, plus an
       extra floor(exp/3) digits for 'f' format.

    */

    if (Py_IS_NAN(val) || Py_IS_INFINITY(val))
        /* 3 for 'inf'/'nan', 1 for sign, 1 for '\0' */
        bufsize = 5;
    else {
        bufsize = 25 + precision;
        if (format_code == 'f' && fabs(val) >= 1.0) {
            frexp(val, &exp);
            bufsize += exp/3;
        }
    }

    buf = PyMem_Malloc(bufsize);
    if (buf == NULL) {
        PyErr_NoMemory();
        return NULL;
    }

    /* Handle nan and inf. */
    if (Py_IS_NAN(val)) {
        strcpy(buf, "nan");
        t = Py_DTST_NAN;
    } else if (Py_IS_INFINITY(val)) {
        if (copysign(1., val) == 1.)
            strcpy(buf, "inf");
        else
            strcpy(buf, "-inf");
        t = Py_DTST_INFINITE;
    } else {
        t = Py_DTST_FINITE;
        if (flags & Py_DTSF_ADD_DOT_0)
            format_code = 'Z';

        PyOS_snprintf(format, sizeof(format), "%%%s.%i%c",
                      (flags & Py_DTSF_ALT ? "#" : ""), precision,
                      format_code);
        _PyOS_ascii_formatd(buf, bufsize, format, val, precision);
    }

    /* Add sign when requested.  It's convenient (esp. when formatting
     complex numbers) to include a sign even for inf and nan. */
    if (flags & Py_DTSF_SIGN && buf[0] != '-') {
        size_t len = strlen(buf);
        /* the bufsize calculations above should ensure that we've got
           space to add a sign */
        assert((size_t)bufsize >= len+2);
        memmove(buf+1, buf, len+1);
        buf[0] = '+';
    }
    if (upper) {
        /* Convert to upper case. */
        char *p1;
        for (p1 = buf; *p1; p1++)
            *p1 = Py_TOUPPER(*p1);
    }

    if (type)
        *type = t;
    return buf;
}

#else

/* _Py_dg_dtoa is available. */

/* I'm using a lookup table here so that I don't have to invent a non-locale
   specific way to convert to uppercase */
#define OFS_INF 0
#define OFS_NAN 1
#define OFS_E 2

/* The lengths of these are known to the code below, so don't change them */
static char *lc_float_strings[] = {
    "inf",
    "nan",
    "e",
};
static char *uc_float_strings[] = {
    "INF",
    "NAN",
    "E",
};


/* Convert a double d to a string, and return a PyMem_Malloc'd block of
   memory contain the resulting string.

   Arguments:
     d is the double to be converted
     format_code is one of 'e', 'f', 'g', 'r'.  'e', 'f' and 'g'
       correspond to '%e', '%f' and '%g';  'r' corresponds to repr.
     mode is one of '0', '2' or '3', and is completely determined by
       format_code: 'e' and 'g' use mode 2; 'f' mode 3, 'r' mode 0.
     precision is the desired precision
     always_add_sign is nonzero if a '+' sign should be included for positive
       numbers
     add_dot_0_if_integer is nonzero if integers in non-exponential form
       should have ".0" added.  Only applies to format codes 'r' and 'g'.
     use_alt_formatting is nonzero if alternative formatting should be
       used.  Only applies to format codes 'e', 'f' and 'g'.  For code 'g',
       at most one of use_alt_formatting and add_dot_0_if_integer should
       be nonzero.
     type, if non-NULL, will be set to one of these constants to identify
       the type of the 'd' argument:
     Py_DTST_FINITE
     Py_DTST_INFINITE
     Py_DTST_NAN

   Returns a PyMem_Malloc'd block of memory containing the resulting string,
    or NULL on error. If NULL is returned, the Python error has been set.
 */

static char *
format_float_short(double d, char format_code,
                   int mode, Py_ssize_t precision,
                   int always_add_sign, int add_dot_0_if_integer,
                   int use_alt_formatting, char **float_strings, int *type)
{
    char *buf = NULL;
    char *p = NULL;
    Py_ssize_t bufsize = 0;
    char *digits, *digits_end;
    int decpt_as_int, sign, exp_len, exp = 0, use_exp = 0;
    Py_ssize_t decpt, digits_len, vdigits_start, vdigits_end;
    _Py_SET_53BIT_PRECISION_HEADER;

    /* _Py_dg_dtoa returns a digit string (no decimal point or exponent).
       Must be matched by a call to _Py_dg_freedtoa. */
    _Py_SET_53BIT_PRECISION_START;
    digits = _Py_dg_dtoa(d, mode, precision, &decpt_as_int, &sign,
                         &digits_end);
    _Py_SET_53BIT_PRECISION_END;

    decpt = (Py_ssize_t)decpt_as_int;
    if (digits == NULL) {
        /* The only failure mode is no memory. */
        PyErr_NoMemory();
        goto exit;
    }
    assert(digits_end != NULL && digits_end >= digits);
    digits_len = digits_end - digits;

    if (digits_len && !Py_ISDIGIT(digits[0])) {
        /* Infinities and nans here; adapt Gay's output,
           so convert Infinity to inf and NaN to nan, and
           ignore sign of nan. Then return. */

        /* ignore the actual sign of a nan */
        if (digits[0] == 'n' || digits[0] == 'N')
            sign = 0;

        /* We only need 5 bytes to hold the result "+inf\0" . */
        bufsize = 5; /* Used later in an assert. */
        buf = (char *)PyMem_Malloc(bufsize);
        if (buf == NULL) {
            PyErr_NoMemory();
            goto exit;
        }
        p = buf;

        if (sign == 1) {
            *p++ = '-';
        }
        else if (always_add_sign) {
            *p++ = '+';
        }
        if (digits[0] == 'i' || digits[0] == 'I') {
            strncpy(p, float_strings[OFS_INF], 3);
            p += 3;

            if (type)
                *type = Py_DTST_INFINITE;
        }
        else if (digits[0] == 'n' || digits[0] == 'N') {
            strncpy(p, float_strings[OFS_NAN], 3);
            p += 3;

            if (type)
                *type = Py_DTST_NAN;
        }
        else {
            /* shouldn't get here: Gay's code should always return
               something starting with a digit, an 'I',  or 'N' */
            assert(0);
        }
        goto exit;
    }

    /* The result must be finite (not inf or nan). */
    if (type)
        *type = Py_DTST_FINITE;


    /* We got digits back, format them.  We may need to pad 'digits'
       either on the left or right (or both) with extra zeros, so in
       general the resulting string has the form

         [<sign>]<zeros><digits><zeros>[<exponent>]

       where either of the <zeros> pieces could be empty, and there's a
       decimal point that could appear either in <digits> or in the
       leading or trailing <zeros>.

       Imagine an infinite 'virtual' string vdigits, consisting of the
       string 'digits' (starting at index 0) padded on both the left and
       right with infinite strings of zeros.  We want to output a slice

         vdigits[vdigits_start : vdigits_end]

       of this virtual string.  Thus if vdigits_start < 0 then we'll end
       up producing some leading zeros; if vdigits_end > digits_len there
       will be trailing zeros in the output.  The next section of code
       determines whether to use an exponent or not, figures out the
       position 'decpt' of the decimal point, and computes 'vdigits_start'
       and 'vdigits_end'. */
    vdigits_end = digits_len;
    switch (format_code) {
    case 'e':
        use_exp = 1;
        vdigits_end = precision;
        break;
    case 'f':
        vdigits_end = decpt + precision;
        break;
    case 'g':
        if (decpt <= -4 || decpt >
            (add_dot_0_if_integer ? precision-1 : precision))
            use_exp = 1;
        if (use_alt_formatting)
            vdigits_end = precision;
        break;
    case 'r':
        /* convert to exponential format at 1e16.  We used to convert
           at 1e17, but that gives odd-looking results for some values
           when a 16-digit 'shortest' repr is padded with bogus zeros.
           For example, repr(2e16+8) would give 20000000000000010.0;
           the true value is 20000000000000008.0. */
        if (decpt <= -4 || decpt > 16)
            use_exp = 1;
        break;
    default:
        PyErr_BadInternalCall();
        goto exit;
    }

    /* if using an exponent, reset decimal point position to 1 and adjust
       exponent accordingly.*/
    if (use_exp) {
        exp = decpt - 1;
        decpt = 1;
    }
    /* ensure vdigits_start < decpt <= vdigits_end, or vdigits_start <
       decpt < vdigits_end if add_dot_0_if_integer and no exponent */
    vdigits_start = decpt <= 0 ? decpt-1 : 0;
    if (!use_exp && add_dot_0_if_integer)
        vdigits_end = vdigits_end > decpt ? vdigits_end : decpt + 1;
    else
        vdigits_end = vdigits_end > decpt ? vdigits_end : decpt;

    /* double check inequalities */
    assert(vdigits_start <= 0 &&
           0 <= digits_len &&
           digits_len <= vdigits_end);
    /* decimal point should be in (vdigits_start, vdigits_end] */
    assert(vdigits_start < decpt && decpt <= vdigits_end);

    /* Compute an upper bound how much memory we need. This might be a few
       chars too long, but no big deal. */
    bufsize =
        /* sign, decimal point and trailing 0 byte */
        3 +

        /* total digit count (including zero padding on both sides) */
        (vdigits_end - vdigits_start) +

        /* exponent "e+100", max 3 numerical digits */
        (use_exp ? 5 : 0);

    /* Now allocate the memory and initialize p to point to the start of
       it. */
    buf = (char *)PyMem_Malloc(bufsize);
    if (buf == NULL) {
        PyErr_NoMemory();
        goto exit;
    }
    p = buf;

    /* Add a negative sign if negative, and a plus sign if non-negative
       and always_add_sign is true. */
    if (sign == 1)
        *p++ = '-';
    else if (always_add_sign)
        *p++ = '+';

    /* note that exactly one of the three 'if' conditions is true,
       so we include exactly one decimal point */
    /* Zero padding on left of digit string */
    if (decpt <= 0) {
        memset(p, '0', decpt-vdigits_start);
        p += decpt - vdigits_start;
        *p++ = '.';
        memset(p, '0', 0-decpt);
        p += 0-decpt;
    }
    else {
        memset(p, '0', 0-vdigits_start);
        p += 0 - vdigits_start;
    }

    /* Digits, with included decimal point */
    if (0 < decpt && decpt <= digits_len) {
        strncpy(p, digits, decpt-0);
        p += decpt-0;
        *p++ = '.';
        strncpy(p, digits+decpt, digits_len-decpt);
        p += digits_len-decpt;
    }
    else {
        strncpy(p, digits, digits_len);
        p += digits_len;
    }

    /* And zeros on the right */
    if (digits_len < decpt) {
        memset(p, '0', decpt-digits_len);
        p += decpt-digits_len;
        *p++ = '.';
        memset(p, '0', vdigits_end-decpt);
        p += vdigits_end-decpt;
    }
    else {
        memset(p, '0', vdigits_end-digits_len);
        p += vdigits_end-digits_len;
    }

    /* Delete a trailing decimal pt unless using alternative formatting. */
    if (p[-1] == '.' && !use_alt_formatting)
        p--;

    /* Now that we've done zero padding, add an exponent if needed. */
    if (use_exp) {
        *p++ = float_strings[OFS_E][0];
        exp_len = sprintf(p, "%+.02d", exp);
        p += exp_len;
    }
  exit:
    if (buf) {
        *p = '\0';
        /* It's too late if this fails, as we've already stepped on
           memory that isn't ours. But it's an okay debugging test. */
        assert(p-buf < bufsize);
    }
    if (digits)
        _Py_dg_freedtoa(digits);

    return buf;
}


PyAPI_FUNC(char *) PyOS_double_to_string(double val,
                                         char format_code,
                                         int precision,
                                         int flags,
                                         int *type)
{
    char **float_strings = lc_float_strings;
    int mode;

    /* Validate format_code, and map upper and lower case. Compute the
       mode and make any adjustments as needed. */
    switch (format_code) {
    /* exponent */
    case 'E':
        float_strings = uc_float_strings;
        format_code = 'e';
        /* Fall through. */
    case 'e':
        mode = 2;
        precision++;
        break;

    /* fixed */
    case 'F':
        float_strings = uc_float_strings;
        format_code = 'f';
        /* Fall through. */
    case 'f':
        mode = 3;
        break;

    /* general */
    case 'G':
        float_strings = uc_float_strings;
        format_code = 'g';
        /* Fall through. */
    case 'g':
        mode = 2;
        /* precision 0 makes no sense for 'g' format; interpret as 1 */
        if (precision == 0)
            precision = 1;
        break;

    /* repr format */
    case 'r':
        mode = 0;
        /* Supplied precision is unused, must be 0. */
        if (precision != 0) {
            PyErr_BadInternalCall();
            return NULL;
        }
        break;

    default:
        PyErr_BadInternalCall();
        return NULL;
    }

    return format_float_short(val, format_code, mode, precision,
                              flags & Py_DTSF_SIGN,
                              flags & Py_DTSF_ADD_DOT_0,
                              flags & Py_DTSF_ALT,
                              float_strings, type);
}
#endif /* ifdef PY_NO_SHORT_FLOAT_REPR */