Modules/_bisectmodule.c

/* Bisection algorithms. Drop in replacement for bisect.py

Converted to C by Dmitry Vasiliev (dima at hlabs.spb.ru).
*/

#define PY_SSIZE_T_CLEAN
#include "Python.h"

/*[clinic input]
module _bisect
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=4d56a2b2033b462b]*/

#include "clinic/_bisectmodule.c.h"

_Py_IDENTIFIER(insert);

static inline Py_ssize_t
internal_bisect_right(PyObject *list, PyObject *item, Py_ssize_t lo, Py_ssize_t hi)
{
    PyObject *litem;
    Py_ssize_t mid;
    int res;

    if (lo < 0) {
        PyErr_SetString(PyExc_ValueError, "lo must be non-negative");
        return -1;
    }
    if (hi == -1) {
        hi = PySequence_Size(list);
        if (hi < 0)
            return -1;
    }
    while (lo < hi) {
        /* The (size_t)cast ensures that the addition and subsequent division
           are performed as unsigned operations, avoiding difficulties from
           signed overflow.  (See issue 13496.) */
        mid = ((size_t)lo + hi) / 2;
        litem = PySequence_GetItem(list, mid);
        if (litem == NULL)
            return -1;
        res = PyObject_RichCompareBool(item, litem, Py_LT);
        Py_DECREF(litem);
        if (res < 0)
            return -1;
        if (res)
            hi = mid;
        else
            lo = mid + 1;
    }
    return lo;
}

/*[clinic input]
_bisect.bisect_right -> Py_ssize_t

    a: object
    x: object
    lo: Py_ssize_t = 0
    hi: Py_ssize_t(c_default='-1', accept={int, NoneType}) = None

Return the index where to insert item x in list a, assuming a is sorted.

The return value i is such that all e in a[:i] have e <= x, and all e in
a[i:] have e > x.  So if x already appears in the list, i points just
beyond the rightmost x already there

Optional args lo (default 0) and hi (default len(a)) bound the
slice of a to be searched.
[clinic start generated code]*/

static Py_ssize_t
_bisect_bisect_right_impl(PyObject *module, PyObject *a, PyObject *x,
                          Py_ssize_t lo, Py_ssize_t hi)
/*[clinic end generated code: output=419e150cf1d2a235 input=e72212b282c83375]*/
{
    return internal_bisect_right(a, x, lo, hi);
}

/*[clinic input]
_bisect.insort_right

    a: object
    x: object
    lo: Py_ssize_t = 0
    hi: Py_ssize_t(c_default='-1', accept={int, NoneType}) = None

Insert item x in list a, and keep it sorted assuming a is sorted.

If x is already in a, insert it to the right of the rightmost x.

Optional args lo (default 0) and hi (default len(a)) bound the
slice of a to be searched.
[clinic start generated code]*/

static PyObject *
_bisect_insort_right_impl(PyObject *module, PyObject *a, PyObject *x,
                          Py_ssize_t lo, Py_ssize_t hi)
/*[clinic end generated code: output=c2caa3d4cd02035a input=d1c45bfa68182669]*/
{
    PyObject *result;
    Py_ssize_t index = internal_bisect_right(a, x, lo, hi);
    if (index < 0)
        return NULL;
    if (PyList_CheckExact(a)) {
        if (PyList_Insert(a, index, x) < 0)
            return NULL;
    }
    else {
        result = _PyObject_CallMethodId(a, &PyId_insert, "nO", index, x);
        if (result == NULL)
            return NULL;
        Py_DECREF(result);
    }

    Py_RETURN_NONE;
}

static inline Py_ssize_t
internal_bisect_left(PyObject *list, PyObject *item, Py_ssize_t lo, Py_ssize_t hi)
{
    PyObject *litem;
    Py_ssize_t mid;
    int res;

    if (lo < 0) {
        PyErr_SetString(PyExc_ValueError, "lo must be non-negative");
        return -1;
    }
    if (hi == -1) {
        hi = PySequence_Size(list);
        if (hi < 0)
            return -1;
    }
    while (lo < hi) {
        /* The (size_t)cast ensures that the addition and subsequent division
           are performed as unsigned operations, avoiding difficulties from
           signed overflow.  (See issue 13496.) */
        mid = ((size_t)lo + hi) / 2;
        litem = PySequence_GetItem(list, mid);
        if (litem == NULL)
            return -1;
        res = PyObject_RichCompareBool(litem, item, Py_LT);
        Py_DECREF(litem);
        if (res < 0)
            return -1;
        if (res)
            lo = mid + 1;
        else
            hi = mid;
    }
    return lo;
}


/*[clinic input]
_bisect.bisect_left -> Py_ssize_t

    a: object
    x: object
    lo: Py_ssize_t = 0
    hi: Py_ssize_t(c_default='-1', accept={int, NoneType}) = None

Return the index where to insert item x in list a, assuming a is sorted.

The return value i is such that all e in a[:i] have e < x, and all e in
a[i:] have e >= x.  So if x already appears in the list, i points just
before the leftmost x already there.

Optional args lo (default 0) and hi (default len(a)) bound the
slice of a to be searched.
[clinic start generated code]*/

static Py_ssize_t
_bisect_bisect_left_impl(PyObject *module, PyObject *a, PyObject *x,
                         Py_ssize_t lo, Py_ssize_t hi)
/*[clinic end generated code: output=af82168bc2856f24 input=2bd90f34afe5609f]*/
{
    return internal_bisect_left(a, x, lo, hi);
}


/*[clinic input]
_bisect.insort_left

    a: object
    x: object
    lo: Py_ssize_t = 0
    hi: Py_ssize_t(c_default='-1', accept={int, NoneType}) = None

Insert item x in list a, and keep it sorted assuming a is sorted.

If x is already in a, insert it to the left of the leftmost x.

Optional args lo (default 0) and hi (default len(a)) bound the
slice of a to be searched.
[clinic start generated code]*/

static PyObject *
_bisect_insort_left_impl(PyObject *module, PyObject *a, PyObject *x,
                         Py_ssize_t lo, Py_ssize_t hi)
/*[clinic end generated code: output=9e8356c0844a182b input=bc4583308bce00cc]*/
{
    PyObject *result;
    Py_ssize_t index = internal_bisect_left(a, x, lo, hi);
    if (index < 0)
        return NULL;
    if (PyList_CheckExact(a)) {
        if (PyList_Insert(a, index, x) < 0)
            return NULL;
    } else {
        result = _PyObject_CallMethodId(a, &PyId_insert, "nO", index, x);
        if (result == NULL)
            return NULL;
        Py_DECREF(result);
    }

    Py_RETURN_NONE;
}

static PyMethodDef bisect_methods[] = {
    _BISECT_BISECT_RIGHT_METHODDEF
    _BISECT_INSORT_RIGHT_METHODDEF
    _BISECT_BISECT_LEFT_METHODDEF
    _BISECT_INSORT_LEFT_METHODDEF
    {NULL, NULL} /* sentinel */
};

PyDoc_STRVAR(module_doc,
"Bisection algorithms.\n\
\n\
This module provides support for maintaining a list in sorted order without\n\
having to sort the list after each insertion. For long lists of items with\n\
expensive comparison operations, this can be an improvement over the more\n\
common approach.\n");


static struct PyModuleDef _bisectmodule = {
    PyModuleDef_HEAD_INIT,
    "_bisect",
    module_doc,
    -1,
    bisect_methods,
    NULL,
    NULL,
    NULL,
    NULL
};

PyMODINIT_FUNC
PyInit__bisect(void)
{
    return PyModule_Create(&_bisectmodule);
}