#include "Python.h"

#include "pycore_call.h" // _PyObject_CallNoArgs()

#include "pycore_initconfig.h" // _Py_DumpPathConfig()

#include "pycore_interp.h" // PyInterpreterState.codec_search_path

#include "pycore_pyerrors.h" // _PyErr_FormatNote()

#include "pycore_pystate.h" // _PyInterpreterState_GET()

#include "pycore_runtime.h" // _Py_ID()

#include "pycore_ucnhash.h" // _PyUnicode_Name_CAPI

#include "pycore_unicodeobject.h" // _PyUnicode_InternMortal()

static const char *codecs_builtin_error_handlers[] = {

"strict", "ignore", "replace",

"xmlcharrefreplace", "backslashreplace", "namereplace",

"surrogatepass", "surrogateescape",

};

const char *Py_hexdigits = "0123456789abcdef";

int PyCodec_Register(PyObject *search_function)

{

PyInterpreterState *interp = _PyInterpreterState_GET();

assert(interp->codecs.initialized);

if (search_function == NULL) {

PyErr_BadArgument();

goto onError;

}

if (!PyCallable_Check(search_function)) {

PyErr_SetString(PyExc_TypeError, "argument must be callable");

goto onError;

}

#ifdef Py_GIL_DISABLED

PyMutex_Lock(&interp->codecs.search_path_mutex);

int ret = PyList_Append(interp->codecs.search_path, search_function);

#ifdef Py_GIL_DISABLED

PyMutex_Unlock(&interp->codecs.search_path_mutex);

return ret;

onError:

return -1;

}

PyCodec_Unregister(PyObject *search_function)

{

PyInterpreterState *interp = _PyInterpreterState_GET();

if (interp->codecs.initialized != 1) {

/* Do nothing if codecs state was cleared (only possible during

return 0;

}

PyObject *codec_search_path = interp->codecs.search_path;

assert(PyList_CheckExact(codec_search_path));

#ifdef Py_GIL_DISABLED

PyMutex_Lock(&interp->codecs.search_path_mutex);

for (Py_ssize_t i = 0; i < PyList_GET_SIZE(codec_search_path); i++) {

if (PyList_GET_ITEM(codec_search_path, i) == search_function) {

// Keep the function alive until after releasing the mutex.

Py_INCREF(search_function);

int ret = PyList_SetSlice(codec_search_path, i, i+1, NULL);

#ifdef Py_GIL_DISABLED

PyMutex_Unlock(&interp->codecs.search_path_mutex);

Py_DECREF(search_function);

assert(interp->codecs.search_cache != NULL);

assert(PyDict_CheckExact(interp->codecs.search_cache));

PyDict_Clear(interp->codecs.search_cache);

return ret;

}

}

#ifdef Py_GIL_DISABLED

PyMutex_Unlock(&interp->codecs.search_path_mutex);

return 0;

}

extern int _Py_normalize_encoding(const char *, char *, size_t);

PyObject *normalizestring(const char *string)

{

size_t len = strlen(string);

char *encoding;

PyObject *v;

if (len > PY_SSIZE_T_MAX) {

PyErr_SetString(PyExc_OverflowError, "string is too large");

return NULL;

}

encoding = PyMem_Malloc(len + 1);

if (encoding == NULL)

return PyErr_NoMemory();

if (!_Py_normalize_encoding(string, encoding, len + 1))

{

PyErr_SetString(PyExc_RuntimeError, "_Py_normalize_encoding() failed");

PyMem_Free(encoding);

return NULL;

}

v = PyUnicode_FromString(encoding);

PyMem_Free(encoding);

return v;

}

PyObject *_PyCodec_Lookup(const char *encoding)

{

if (encoding == NULL) {

PyErr_BadArgument();

return NULL;

}

PyInterpreterState *interp = _PyInterpreterState_GET();

assert(interp->codecs.initialized);

/* Convert the encoding to a normalized Python string: all

PyObject *v = normalizestring(encoding);

if (v == NULL) {

return NULL;

}

/* Intern the string. We'll make it immortal later if lookup succeeds. */

_PyUnicode_InternMortal(interp, &v);

/* First, try to lookup the name in the registry dictionary */

PyObject *result;

if (PyDict_GetItemRef(interp->codecs.search_cache, v, &result) < 0) {

goto onError;

}

if (result != NULL) {

Py_DECREF(v);

return result;

}

/* Next, scan the search functions in order of registration */

const Py_ssize_t len = PyList_Size(interp->codecs.search_path);

if (len < 0)

goto onError;

if (len == 0) {

PyErr_SetString(PyExc_LookupError,

"no codec search functions registered: "

"can't find encoding");

goto onError;

}

Py_ssize_t i;

for (i = 0; i < len; i++) {

PyObject *func;

func = PyList_GetItemRef(interp->codecs.search_path, i);

if (func == NULL)

goto onError;

result = PyObject_CallOneArg(func, v);

Py_DECREF(func);

if (result == NULL)

goto onError;

if (result == Py_None) {

Py_CLEAR(result);

continue;

}

if (!PyTuple_Check(result) || PyTuple_GET_SIZE(result) != 4) {

PyErr_SetString(PyExc_TypeError,

"codec search functions must return 4-tuples");

Py_DECREF(result);

goto onError;

}

break;

}

if (result == NULL) {

/* XXX Perhaps we should cache misses too ? */

PyErr_Format(PyExc_LookupError,

"unknown encoding: %s", encoding);

goto onError;

}

_PyUnicode_InternImmortal(interp, &v);

/* Cache and return the result */

if (PyDict_SetItem(interp->codecs.search_cache, v, result) < 0) {

Py_DECREF(result);

goto onError;

}

Py_DECREF(v);

return result;

onError:

Py_DECREF(v);

return NULL;

}

int PyCodec_KnownEncoding(const char *encoding)

{

PyObject *codecs;

codecs = _PyCodec_Lookup(encoding);

if (!codecs) {

PyErr_Clear();

return 0;

}

else {

Py_DECREF(codecs);

return 1;

}

}

PyObject *args_tuple(PyObject *object,

const char *errors)

{

PyObject *args;

args = PyTuple_New(1 + (errors != NULL));

if (args == NULL)

return NULL;

PyTuple_SET_ITEM(args, 0, Py_NewRef(object));

if (errors) {

PyObject *v;

v = PyUnicode_FromString(errors);

if (v == NULL) {

Py_DECREF(args);

return NULL;

}

PyTuple_SET_ITEM(args, 1, v);

}

return args;

}

PyObject *codec_getitem(const char *encoding, int index)

{

PyObject *codecs;

PyObject *v;

codecs = _PyCodec_Lookup(encoding);

if (codecs == NULL)

return NULL;

v = PyTuple_GET_ITEM(codecs, index);

Py_DECREF(codecs);

return Py_NewRef(v);

}

PyObject *codec_makeincrementalcodec(PyObject *codec_info,

const char *errors,

const char *attrname)

{

PyObject *ret, *inccodec;

inccodec = PyObject_GetAttrString(codec_info, attrname);

if (inccodec == NULL)

return NULL;

if (errors)

ret = PyObject_CallFunction(inccodec, "s", errors);

else

ret = _PyObject_CallNoArgs(inccodec);

Py_DECREF(inccodec);

return ret;

}

PyObject *codec_getincrementalcodec(const char *encoding,

const char *errors,

const char *attrname)

{

PyObject *codec_info, *ret;

codec_info = _PyCodec_Lookup(encoding);

if (codec_info == NULL)

return NULL;

ret = codec_makeincrementalcodec(codec_info, errors, attrname);

Py_DECREF(codec_info);

return ret;

}

PyObject *codec_getstreamcodec(const char *encoding,

PyObject *stream,

const char *errors,

const int index)

{

PyObject *codecs, *streamcodec, *codeccls;

codecs = _PyCodec_Lookup(encoding);

if (codecs == NULL)

return NULL;

codeccls = PyTuple_GET_ITEM(codecs, index);

if (errors != NULL)

streamcodec = PyObject_CallFunction(codeccls, "Os", stream, errors);

else

streamcodec = PyObject_CallOneArg(codeccls, stream);

Py_DECREF(codecs);

return streamcodec;

}

PyObject *_PyCodecInfo_GetIncrementalDecoder(PyObject *codec_info,

const char *errors)

{

return codec_makeincrementalcodec(codec_info, errors,

"incrementaldecoder");

}

PyObject *_PyCodecInfo_GetIncrementalEncoder(PyObject *codec_info,

const char *errors)

{

return codec_makeincrementalcodec(codec_info, errors,

"incrementalencoder");

}

PyObject *PyCodec_Encoder(const char *encoding)

{

return codec_getitem(encoding, 0);

}

PyObject *PyCodec_Decoder(const char *encoding)

{

return codec_getitem(encoding, 1);

}

PyObject *PyCodec_IncrementalEncoder(const char *encoding,

const char *errors)

{

return codec_getincrementalcodec(encoding, errors, "incrementalencoder");

}

PyObject *PyCodec_IncrementalDecoder(const char *encoding,

const char *errors)

{

return codec_getincrementalcodec(encoding, errors, "incrementaldecoder");

}

PyObject *PyCodec_StreamReader(const char *encoding,

PyObject *stream,

const char *errors)

{

return codec_getstreamcodec(encoding, stream, errors, 2);

}

PyObject *PyCodec_StreamWriter(const char *encoding,

PyObject *stream,

const char *errors)

{

return codec_getstreamcodec(encoding, stream, errors, 3);

}

static PyObject *

_PyCodec_EncodeInternal(PyObject *object,

PyObject *encoder,

const char *encoding,

const char *errors)

{

PyObject *args = NULL, *result = NULL;

PyObject *v = NULL;

args = args_tuple(object, errors);

if (args == NULL)

goto onError;

result = PyObject_Call(encoder, args, NULL);

if (result == NULL) {

_PyErr_FormatNote("%s with '%s' codec failed", "encoding", encoding);

goto onError;

}

if (!PyTuple_Check(result) ||

PyTuple_GET_SIZE(result) != 2) {

PyErr_SetString(PyExc_TypeError,

"encoder must return a tuple (object, integer)");

goto onError;

}

v = Py_NewRef(PyTuple_GET_ITEM(result,0));

/* We don't check or use the second (integer) entry. */

Py_DECREF(args);

Py_DECREF(encoder);

Py_DECREF(result);

return v;

onError:

Py_XDECREF(result);

Py_XDECREF(args);

Py_XDECREF(encoder);

return NULL;

}

static PyObject *

_PyCodec_DecodeInternal(PyObject *object,

PyObject *decoder,

const char *encoding,

const char *errors)

{

PyObject *args = NULL, *result = NULL;

PyObject *v;

args = args_tuple(object, errors);

if (args == NULL)

goto onError;

result = PyObject_Call(decoder, args, NULL);

if (result == NULL) {

_PyErr_FormatNote("%s with '%s' codec failed", "decoding", encoding);

goto onError;

}

if (!PyTuple_Check(result) ||

PyTuple_GET_SIZE(result) != 2) {

PyErr_SetString(PyExc_TypeError,

"decoder must return a tuple (object,integer)");

goto onError;

}

v = Py_NewRef(PyTuple_GET_ITEM(result,0));

/* We don't check or use the second (integer) entry. */

Py_DECREF(args);

Py_DECREF(decoder);

Py_DECREF(result);

return v;

onError:

Py_XDECREF(args);

Py_XDECREF(decoder);

Py_XDECREF(result);

return NULL;

}

PyObject *PyCodec_Encode(PyObject *object,

const char *encoding,

const char *errors)

{

PyObject *encoder;

encoder = PyCodec_Encoder(encoding);

if (encoder == NULL)

return NULL;

return _PyCodec_EncodeInternal(object, encoder, encoding, errors);

}

PyObject *PyCodec_Decode(PyObject *object,

const char *encoding,

const char *errors)

{

PyObject *decoder;

decoder = PyCodec_Decoder(encoding);

if (decoder == NULL)

return NULL;

return _PyCodec_DecodeInternal(object, decoder, encoding, errors);

}

PyObject * _PyCodec_LookupTextEncoding(const char *encoding,

const char *alternate_command)

{

PyObject *codec;

PyObject *attr;

int is_text_codec;

codec = _PyCodec_Lookup(encoding);

if (codec == NULL)

return NULL;

/* Backwards compatibility: assume any raw tuple describes a text

if (!PyTuple_CheckExact(codec)) {

if (PyObject_GetOptionalAttr(codec, &_Py_ID(_is_text_encoding), &attr) < 0) {

Py_DECREF(codec);

return NULL;

}

if (attr != NULL) {

is_text_codec = PyObject_IsTrue(attr);

Py_DECREF(attr);

if (is_text_codec <= 0) {

Py_DECREF(codec);

if (!is_text_codec) {

if (alternate_command != NULL) {

PyErr_Format(PyExc_LookupError,

"'%.400s' is not a text encoding; "

"use %s to handle arbitrary codecs",

encoding, alternate_command);

}

else {

PyErr_Format(PyExc_LookupError,

"'%.400s' is not a text encoding",

encoding);

}

}

return NULL;

}

}

}

/* This appears to be a valid text encoding */

return codec;

}

PyObject *codec_getitem_checked(const char *encoding,

const char *alternate_command,

int index)

{

PyObject *codec;

PyObject *v;

codec = _PyCodec_LookupTextEncoding(encoding, alternate_command);

if (codec == NULL)

return NULL;

v = Py_NewRef(PyTuple_GET_ITEM(codec, index));

Py_DECREF(codec);

return v;

}

static PyObject * _PyCodec_TextEncoder(const char *encoding)

{

return codec_getitem_checked(encoding, "codecs.encode()", 0);

}

static PyObject * _PyCodec_TextDecoder(const char *encoding)

{

return codec_getitem_checked(encoding, "codecs.decode()", 1);

}

PyObject *_PyCodec_EncodeText(PyObject *object,

const char *encoding,

const char *errors)

{

PyObject *encoder;

encoder = _PyCodec_TextEncoder(encoding);

if (encoder == NULL)

return NULL;

return _PyCodec_EncodeInternal(object, encoder, encoding, errors);

}

PyObject *_PyCodec_DecodeText(PyObject *object,

const char *encoding,

const char *errors)

{

PyObject *decoder;

decoder = _PyCodec_TextDecoder(encoding);

if (decoder == NULL)

return NULL;

return _PyCodec_DecodeInternal(object, decoder, encoding, errors);

}

int PyCodec_RegisterError(const char *name, PyObject *error)

{

PyInterpreterState *interp = _PyInterpreterState_GET();

assert(interp->codecs.initialized);

if (!PyCallable_Check(error)) {

PyErr_SetString(PyExc_TypeError, "handler must be callable");

return -1;

}

return PyDict_SetItemString(interp->codecs.error_registry,

name, error);

}

int _PyCodec_UnregisterError(const char *name)

{

for (size_t i = 0; i < Py_ARRAY_LENGTH(codecs_builtin_error_handlers); ++i) {

if (strcmp(name, codecs_builtin_error_handlers[i]) == 0) {

PyErr_Format(PyExc_ValueError,

"cannot un-register built-in error handler '%s'", name);

return -1;

}

}

PyInterpreterState *interp = _PyInterpreterState_GET();

assert(interp->codecs.initialized);

return PyDict_PopString(interp->codecs.error_registry, name, NULL);

}

PyObject *PyCodec_LookupError(const char *name)

{

PyInterpreterState *interp = _PyInterpreterState_GET();

assert(interp->codecs.initialized);

if (name==NULL)

name = "strict";

PyObject *handler;

if (PyDict_GetItemStringRef(interp->codecs.error_registry, name, &handler) < 0) {

return NULL;

}

if (handler == NULL) {

PyErr_Format(PyExc_LookupError, "unknown error handler name '%.400s'", name);

return NULL;

}

return handler;

}

static inline void

wrong_exception_type(PyObject *exc)

{

PyErr_Format(PyExc_TypeError,

"don't know how to handle %T in error callback", exc);

}

#define _PyIsUnicodeEncodeError(EXC) \

PyObject_TypeCheck(EXC, (PyTypeObject *)PyExc_UnicodeEncodeError)

#define _PyIsUnicodeDecodeError(EXC) \

PyObject_TypeCheck(EXC, (PyTypeObject *)PyExc_UnicodeDecodeError)

#define _PyIsUnicodeTranslateError(EXC) \

PyObject_TypeCheck(EXC, (PyTypeObject *)PyExc_UnicodeTranslateError)

static inline Py_ssize_t

codec_handler_unicode_hex_width(Py_UCS4 ch)

{

if (ch >= 0x10000) {

// format: '\\' + 'U' + 8 hex digits

return 1 + 1 + 8;

}

else if (ch >= 0x100) {

// format: '\\' + 'u' + 4 hex digits

return 1 + 1 + 4;

}

else {

// format: '\\' + 'x' + 2 hex digits

return 1 + 1 + 2;

}

}

static inline void

codec_handler_write_unicode_hex(Py_UCS1 **p, Py_UCS4 ch)

{

*(*p)++ = '\\';

if (ch >= 0x10000) {

*(*p)++ = 'U';

*(*p)++ = Py_hexdigits[(ch >> 28) & 0xf];

*(*p)++ = Py_hexdigits[(ch >> 24) & 0xf];

*(*p)++ = Py_hexdigits[(ch >> 20) & 0xf];

*(*p)++ = Py_hexdigits[(ch >> 16) & 0xf];

*(*p)++ = Py_hexdigits[(ch >> 12) & 0xf];

*(*p)++ = Py_hexdigits[(ch >> 8) & 0xf];

}

else if (ch >= 0x100) {

*(*p)++ = 'u';

*(*p)++ = Py_hexdigits[(ch >> 12) & 0xf];

*(*p)++ = Py_hexdigits[(ch >> 8) & 0xf];

}

else {

*(*p)++ = 'x';

}

*(*p)++ = Py_hexdigits[(ch >> 4) & 0xf];

*(*p)++ = Py_hexdigits[ch & 0xf];

}

static inline int

n_decimal_digits_for_codepoint(Py_UCS4 ch)

{

if (ch < 10) return 1;

if (ch < 100) return 2;

if (ch < 1000) return 3;

if (ch < 10000) return 4;

if (ch < 100000) return 5;

if (ch < 1000000) return 6;

if (ch < 10000000) return 7;

// Unicode codepoints are limited to 1114111 (7 decimal digits)

Py_UNREACHABLE();

}

static PyObject *

codec_handler_unicode_replacement_character(Py_ssize_t count)

{

PyObject *res = PyUnicode_New(count, Py_UNICODE_REPLACEMENT_CHARACTER);

if (res == NULL) {

return NULL;

}

assert(count == 0 || PyUnicode_KIND(res) == PyUnicode_2BYTE_KIND);

Py_UCS2 *outp = PyUnicode_2BYTE_DATA(res);

for (Py_ssize_t i = 0; i < count; ++i) {

outp[i] = Py_UNICODE_REPLACEMENT_CHARACTER;

}

assert(_PyUnicode_CheckConsistency(res, 1));

return res;

}

PyObject *PyCodec_StrictErrors(PyObject *exc)

{

if (PyExceptionInstance_Check(exc)) {

PyErr_SetObject(PyExceptionInstance_Class(exc), exc);

}

else {

PyErr_SetString(PyExc_TypeError, "codec must pass exception instance");

}

return NULL;

}

static PyObject *

_PyCodec_IgnoreError(PyObject *exc, int as_bytes)

{

Py_ssize_t end;

if (_PyUnicodeError_GetParams(exc, NULL, NULL, NULL,

&end, NULL, as_bytes) < 0)

{

return NULL;

}

return Py_BuildValue("(Nn)", Py_GetConstant(Py_CONSTANT_EMPTY_STR), end);

}

PyObject *PyCodec_IgnoreErrors(PyObject *exc)

{

if (_PyIsUnicodeEncodeError(exc) || _PyIsUnicodeTranslateError(exc)) {

return _PyCodec_IgnoreError(exc, false);

}

else if (_PyIsUnicodeDecodeError(exc)) {

return _PyCodec_IgnoreError(exc, true);

}

else {

wrong_exception_type(exc);

return NULL;

}

}

static PyObject *

_PyCodec_ReplaceUnicodeEncodeError(PyObject *exc)

{

Py_ssize_t start, end, slen;

if (_PyUnicodeError_GetParams(exc, NULL, NULL,

&start, &end, &slen, false) < 0)

{

return NULL;

}

PyObject *res = PyUnicode_New(slen, '?');

if (res == NULL) {

return NULL;

}

assert(PyUnicode_KIND(res) == PyUnicode_1BYTE_KIND);

Py_UCS1 *outp = PyUnicode_1BYTE_DATA(res);

memset(outp, '?', sizeof(Py_UCS1) * slen);

assert(_PyUnicode_CheckConsistency(res, 1));

return Py_BuildValue("(Nn)", res, end);

}

static PyObject *

_PyCodec_ReplaceUnicodeDecodeError(PyObject *exc)

{

Py_ssize_t end;

if (PyUnicodeDecodeError_GetEnd(exc, &end) < 0) {

return NULL;

}

PyObject *res = codec_handler_unicode_replacement_character(1);

if (res == NULL) {

return NULL;

}

return Py_BuildValue("(Nn)", res, end);

}

static PyObject *

_PyCodec_ReplaceUnicodeTranslateError(PyObject *exc)

{

Py_ssize_t start, end, slen;

if (_PyUnicodeError_GetParams(exc, NULL, NULL,

&start, &end, &slen, false) < 0)

{

return NULL;

}

PyObject *res = codec_handler_unicode_replacement_character(slen);

if (res == NULL) {

return NULL;

}

return Py_BuildValue("(Nn)", res, end);

}

PyObject *PyCodec_ReplaceErrors(PyObject *exc)

{

if (_PyIsUnicodeEncodeError(exc)) {

return _PyCodec_ReplaceUnicodeEncodeError(exc);

}

else if (_PyIsUnicodeDecodeError(exc)) {

return _PyCodec_ReplaceUnicodeDecodeError(exc);

}

else if (_PyIsUnicodeTranslateError(exc)) {

return _PyCodec_ReplaceUnicodeTranslateError(exc);

}

else {

wrong_exception_type(exc);

return NULL;

}

}

PyObject *PyCodec_XMLCharRefReplaceErrors(PyObject *exc)

{

if (!_PyIsUnicodeEncodeError(exc)) {

wrong_exception_type(exc);

return NULL;

}

PyObject *obj;

Py_ssize_t objlen, start, end, slen;

if (_PyUnicodeError_GetParams(exc,

&obj, &objlen,

&start, &end, &slen, false) < 0)

{

return NULL;

}

// The number of characters that each character 'ch' contributes

// in the result is 2 + k + 1, where k = min{t >= 1 | 10^t > ch}

// and will be formatted as "&#" + DIGITS + ";". Since the Unicode

// range is below 10^7, each "block" requires at most 2 + 7 + 1

// characters.

if (slen > PY_SSIZE_T_MAX / (2 + 7 + 1)) {

end = start + PY_SSIZE_T_MAX / (2 + 7 + 1);

end = Py_MIN(end, objlen);

slen = Py_MAX(0, end - start);

}

Py_ssize_t ressize = 0;

for (Py_ssize_t i = start; i < end; ++i) {

Py_UCS4 ch = PyUnicode_READ_CHAR(obj, i);

int k = n_decimal_digits_for_codepoint(ch);

assert(k != 0);

assert(k <= 7);

ressize += 2 + k + 1;

}

/* allocate replacement */

PyObject *res = PyUnicode_New(ressize, 127);

if (res == NULL) {

Py_DECREF(obj);

return NULL;

}

Py_UCS1 *outp = PyUnicode_1BYTE_DATA(res);

/* generate replacement */

for (Py_ssize_t i = start; i < end; ++i) {

Py_UCS4 ch = PyUnicode_READ_CHAR(obj, i);

/*

*outp++ = '&';

*outp++ = '#';

Py_UCS1 *digit_end = outp + n_decimal_digits_for_codepoint(ch);

for (Py_UCS1 *p_digit = digit_end - 1; p_digit >= outp; --p_digit) {

*p_digit = '0' + (ch % 10);

ch /= 10;

}

assert(ch == 0);

outp = digit_end;

*outp++ = ';';

}

assert(_PyUnicode_CheckConsistency(res, 1));

PyObject *restuple = Py_BuildValue("(Nn)", res, end);

Py_DECREF(obj);

return restuple;

}

static PyObject *

_PyCodec_BackslashReplaceUnicodeEncodeError(PyObject *exc)

{

PyObject *obj;

Py_ssize_t objlen, start, end, slen;

if (_PyUnicodeError_GetParams(exc,

&obj, &objlen,

&start, &end, &slen, false) < 0)

{

return NULL;

}

// The number of characters that each character 'ch' contributes

// in the result is 1 + 1 + k, where k >= min{t >= 1 | 16^t > ch}

// and will be formatted as "\\" + ('U'|'u'|'x') + HEXDIGITS,

// where the number of hexdigits is either 2, 4, or 8 (not 6).

// Since the Unicode range is below 10^7, we choose k = 8 whence

// each "block" requires at most 1 + 1 + 8 characters.

if (slen > PY_SSIZE_T_MAX / (1 + 1 + 8)) {

end = start + PY_SSIZE_T_MAX / (1 + 1 + 8);

end = Py_MIN(end, objlen);

slen = Py_MAX(0, end - start);

}

Py_ssize_t ressize = 0;

for (Py_ssize_t i = start; i < end; ++i) {

Py_UCS4 c = PyUnicode_READ_CHAR(obj, i);

ressize += codec_handler_unicode_hex_width(c);

}