#if STRINGLIB_IS_UNICODE

#error join.h only compatible with byte-wise strings

Py_LOCAL_INLINE(PyObject *)

STRINGLIB(bytes_join)(PyObject *sep, PyObject *iterable)

{

const char *sepstr = STRINGLIB_STR(sep);

Py_ssize_t seplen = STRINGLIB_LEN(sep);

PyObject *res = NULL;

char *p;

Py_ssize_t seqlen = 0;

Py_ssize_t sz = 0;

Py_ssize_t i, nbufs;

PyObject *seq, *item;

Py_buffer *buffers = NULL;

#define NB_STATIC_BUFFERS 10

Py_buffer static_buffers[NB_STATIC_BUFFERS];

#define GIL_THRESHOLD 1048576

int drop_gil = 1;

PyThreadState *save = NULL;

seq = PySequence_Fast(iterable, "can only join an iterable");

if (seq == NULL) {

return NULL;

}

seqlen = PySequence_Fast_GET_SIZE(seq);

if (seqlen == 0) {

Py_DECREF(seq);

return STRINGLIB_NEW(NULL, 0);

}

#if !STRINGLIB_MUTABLE

if (seqlen == 1) {

item = PySequence_Fast_GET_ITEM(seq, 0);

if (STRINGLIB_CHECK_EXACT(item)) {

Py_INCREF(item);

Py_DECREF(seq);

return item;

}

}

if (seqlen > NB_STATIC_BUFFERS) {

buffers = PyMem_NEW(Py_buffer, seqlen);

if (buffers == NULL) {

Py_DECREF(seq);

PyErr_NoMemory();

return NULL;

}

}

else {

buffers = static_buffers;

}

/* Here is the general case. Do a pre-pass to figure out the total

for (i = 0, nbufs = 0; i < seqlen; i++) {

Py_ssize_t itemlen;

item = PySequence_Fast_GET_ITEM(seq, i);

if (PyBytes_CheckExact(item)) {

/* Fast path. */

buffers[i].obj = Py_NewRef(item);

buffers[i].buf = PyBytes_AS_STRING(item);

buffers[i].len = PyBytes_GET_SIZE(item);

}

else {

/* item is only borrowed; its __buffer__() may run Python that

Py_INCREF(item);

if (PyObject_GetBuffer(item, &buffers[i], PyBUF_SIMPLE) != 0) {

Py_DECREF(item);

PyErr_Format(PyExc_TypeError,

"sequence item %zd: expected a bytes-like object, "

"%.80s found",

i, Py_TYPE(item)->tp_name);

goto error;

}

Py_DECREF(item);

/* If the backing objects are mutable, then dropping the GIL

drop_gil = 0;

}

nbufs = i + 1; /* for error cleanup */

itemlen = buffers[i].len;

if (itemlen > PY_SSIZE_T_MAX - sz) {

PyErr_SetString(PyExc_OverflowError,

"join() result is too long");

goto error;

}

sz += itemlen;

if (i != 0) {

if (seplen > PY_SSIZE_T_MAX - sz) {

PyErr_SetString(PyExc_OverflowError,

"join() result is too long");

goto error;

}

sz += seplen;

}

if (seqlen != PySequence_Fast_GET_SIZE(seq)) {

PyErr_SetString(PyExc_RuntimeError,

"sequence changed size during iteration");

goto error;

}

}

/* Allocate result space. */

res = STRINGLIB_NEW(NULL, sz);

if (res == NULL)

goto error;

/* Catenate everything. */

p = STRINGLIB_STR(res);

if (sz < GIL_THRESHOLD) {

drop_gil = 0; /* Benefits are likely outweighed by the overheads */

}

if (drop_gil) {

save = PyEval_SaveThread();

}

if (!seplen) {

/* fast path */

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

Py_ssize_t n = buffers[i].len;

char *q = buffers[i].buf;

memcpy(p, q, n);

p += n;

}

}

else {

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

Py_ssize_t n;

char *q;

if (i) {

memcpy(p, sepstr, seplen);

p += seplen;

}

n = buffers[i].len;

q = buffers[i].buf;

memcpy(p, q, n);

p += n;

}

}

if (drop_gil) {

PyEval_RestoreThread(save);

}

goto done;

error:

res = NULL;

done:

Py_DECREF(seq);

for (i = 0; i < nbufs; i++)

PyBuffer_Release(&buffers[i]);

if (buffers != static_buffers)

PyMem_Free(buffers);

return res;

}

#undef NB_STATIC_BUFFERS

#undef GIL_THRESHOLD