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@littleq0903
Forked from kjelly/gist:7252623
Created October 31, 2013 17:46
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static PyObject *
string_concatenate(PyObject *v, PyObject *w,
PyFrameObject *f, unsigned char *next_instr)
{
/* This function implements 'variable += expr' when both arguments
are strings. */
Py_ssize_t v_len = PyString_GET_SIZE(v);
Py_ssize_t w_len = PyString_GET_SIZE(w);
Py_ssize_t new_len = v_len + w_len;
if (new_len < 0) {
PyErr_SetString(PyExc_OverflowError,
"strings are too large to concat");
return NULL;
}
if (v->ob_refcnt == 2) {
/* In the common case, there are 2 references to the value
* stored in 'variable' when the += is performed: one on the
* value stack (in 'v') and one still stored in the
* 'variable'. We try to delete the variable now to reduce
* the refcnt to 1.
*/
switch (*next_instr) {
case STORE_FAST:
{
int oparg = PEEKARG();
PyObject **fastlocals = f->f_localsplus;
if (GETLOCAL(oparg) == v)
SETLOCAL(oparg, NULL);
break;
}
case STORE_DEREF:
{
PyObject **freevars = (f->f_localsplus +
f->f_code->co_nlocals);
PyObject *c = freevars[PEEKARG()];
if (PyCell_GET(c) == v)
PyCell_Set(c, NULL);
break;
}
case STORE_NAME:
{
PyObject *names = f->f_code->co_names;
PyObject *name = GETITEM(names, PEEKARG());
PyObject *locals = f->f_locals;
if (PyDict_CheckExact(locals) &&
PyDict_GetItem(locals, name) == v) {
if (PyDict_DelItem(locals, name) != 0) {
PyErr_Clear();
}
}
break;
}
}
}
if (v->ob_refcnt == 1 && !PyString_CHECK_INTERNED(v)) {
/* Now we own the last reference to 'v', so we can resize it
* in-place.
*/
if (_PyString_Resize(&v, new_len) != 0) {
/* XXX if _PyString_Resize() fails, 'v' has been
* deallocated so it cannot be put back into
* 'variable'. The MemoryError is raised when there
* is no value in 'variable', which might (very
* remotely) be a cause of incompatibilities.
*/
return NULL;
}
/* copy 'w' into the newly allocated area of 'v' */
memcpy(PyString_AS_STRING(v) + v_len,
PyString_AS_STRING(w), w_len);
return v;
}
else {
/* When in-place resizing is not an option. */
PyString_Concat(&v, w);
return v;
}
}
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