246 lines
7.2 KiB
C
246 lines
7.2 KiB
C
/* Bisection algorithms. Drop in replacement for bisect.py
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Converted to C by Dmitry Vasiliev (dima at hlabs.spb.ru).
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*/
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#include "Python.h"
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static Py_ssize_t
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internal_bisect_right(PyObject *list, PyObject *item, Py_ssize_t lo, Py_ssize_t hi)
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{
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PyObject *litem;
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Py_ssize_t mid, res;
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if (lo < 0) {
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PyErr_SetString(PyExc_ValueError, "lo must be non-negative");
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return -1;
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}
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if (hi == -1) {
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hi = PySequence_Size(list);
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if (hi < 0)
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return -1;
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}
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while (lo < hi) {
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/* The (size_t)cast ensures that the addition and subsequent division
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are performed as unsigned operations, avoiding difficulties from
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signed overflow. (See issue 13496.) */
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mid = ((size_t)lo + hi) / 2;
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litem = PySequence_GetItem(list, mid);
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if (litem == NULL)
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return -1;
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res = PyObject_RichCompareBool(item, litem, Py_LT);
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Py_DECREF(litem);
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if (res < 0)
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return -1;
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if (res)
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hi = mid;
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else
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lo = mid + 1;
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}
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return lo;
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}
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static PyObject *
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bisect_right(PyObject *self, PyObject *args, PyObject *kw)
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{
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PyObject *list, *item;
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Py_ssize_t lo = 0;
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Py_ssize_t hi = -1;
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Py_ssize_t index;
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static char *keywords[] = {"a", "x", "lo", "hi", NULL};
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if (!PyArg_ParseTupleAndKeywords(args, kw, "OO|nn:bisect_right",
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keywords, &list, &item, &lo, &hi))
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return NULL;
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index = internal_bisect_right(list, item, lo, hi);
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if (index < 0)
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return NULL;
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return PyInt_FromSsize_t(index);
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}
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PyDoc_STRVAR(bisect_right_doc,
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"bisect(a, x[, lo[, hi]]) -> index\n\
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bisect_right(a, x[, lo[, hi]]) -> index\n\
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\n\
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Return the index where to insert item x in list a, assuming a is sorted.\n\
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\n\
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The return value i is such that all e in a[:i] have e <= x, and all e in\n\
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a[i:] have e > x. So if x already appears in the list, i points just\n\
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beyond the rightmost x already there\n\
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\n\
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Optional args lo (default 0) and hi (default len(a)) bound the\n\
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slice of a to be searched.\n");
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static PyObject *
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insort_right(PyObject *self, PyObject *args, PyObject *kw)
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{
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PyObject *list, *item, *result;
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Py_ssize_t lo = 0;
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Py_ssize_t hi = -1;
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Py_ssize_t index;
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static char *keywords[] = {"a", "x", "lo", "hi", NULL};
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if (!PyArg_ParseTupleAndKeywords(args, kw, "OO|nn:insort_right",
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keywords, &list, &item, &lo, &hi))
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return NULL;
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index = internal_bisect_right(list, item, lo, hi);
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if (index < 0)
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return NULL;
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if (PyList_CheckExact(list)) {
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if (PyList_Insert(list, index, item) < 0)
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return NULL;
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} else {
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result = PyObject_CallMethod(list, "insert", "nO",
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index, item);
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if (result == NULL)
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return NULL;
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Py_DECREF(result);
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}
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Py_RETURN_NONE;
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}
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PyDoc_STRVAR(insort_right_doc,
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"insort(a, x[, lo[, hi]])\n\
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insort_right(a, x[, lo[, hi]])\n\
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\n\
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Insert item x in list a, and keep it sorted assuming a is sorted.\n\
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\n\
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If x is already in a, insert it to the right of the rightmost x.\n\
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\n\
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Optional args lo (default 0) and hi (default len(a)) bound the\n\
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slice of a to be searched.\n");
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static Py_ssize_t
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internal_bisect_left(PyObject *list, PyObject *item, Py_ssize_t lo, Py_ssize_t hi)
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{
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PyObject *litem;
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Py_ssize_t mid, res;
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if (lo < 0) {
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PyErr_SetString(PyExc_ValueError, "lo must be non-negative");
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return -1;
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}
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if (hi == -1) {
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hi = PySequence_Size(list);
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if (hi < 0)
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return -1;
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}
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while (lo < hi) {
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/* The (size_t)cast ensures that the addition and subsequent division
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are performed as unsigned operations, avoiding difficulties from
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signed overflow. (See issue 13496.) */
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mid = ((size_t)lo + hi) / 2;
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litem = PySequence_GetItem(list, mid);
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if (litem == NULL)
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return -1;
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res = PyObject_RichCompareBool(litem, item, Py_LT);
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Py_DECREF(litem);
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if (res < 0)
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return -1;
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if (res)
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lo = mid + 1;
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else
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hi = mid;
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}
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return lo;
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}
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static PyObject *
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bisect_left(PyObject *self, PyObject *args, PyObject *kw)
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{
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PyObject *list, *item;
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Py_ssize_t lo = 0;
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Py_ssize_t hi = -1;
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Py_ssize_t index;
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static char *keywords[] = {"a", "x", "lo", "hi", NULL};
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if (!PyArg_ParseTupleAndKeywords(args, kw, "OO|nn:bisect_left",
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keywords, &list, &item, &lo, &hi))
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return NULL;
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index = internal_bisect_left(list, item, lo, hi);
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if (index < 0)
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return NULL;
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return PyInt_FromSsize_t(index);
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}
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PyDoc_STRVAR(bisect_left_doc,
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"bisect_left(a, x[, lo[, hi]]) -> index\n\
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\n\
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Return the index where to insert item x in list a, assuming a is sorted.\n\
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\n\
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The return value i is such that all e in a[:i] have e < x, and all e in\n\
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a[i:] have e >= x. So if x already appears in the list, i points just\n\
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before the leftmost x already there.\n\
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\n\
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Optional args lo (default 0) and hi (default len(a)) bound the\n\
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slice of a to be searched.\n");
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static PyObject *
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insort_left(PyObject *self, PyObject *args, PyObject *kw)
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{
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PyObject *list, *item, *result;
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Py_ssize_t lo = 0;
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Py_ssize_t hi = -1;
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Py_ssize_t index;
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static char *keywords[] = {"a", "x", "lo", "hi", NULL};
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if (!PyArg_ParseTupleAndKeywords(args, kw, "OO|nn:insort_left",
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keywords, &list, &item, &lo, &hi))
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return NULL;
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index = internal_bisect_left(list, item, lo, hi);
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if (index < 0)
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return NULL;
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if (PyList_CheckExact(list)) {
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if (PyList_Insert(list, index, item) < 0)
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return NULL;
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} else {
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result = PyObject_CallMethod(list, "insert", "nO",
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index, item);
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if (result == NULL)
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return NULL;
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Py_DECREF(result);
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}
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Py_RETURN_NONE;
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}
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PyDoc_STRVAR(insort_left_doc,
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"insort_left(a, x[, lo[, hi]])\n\
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\n\
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Insert item x in list a, and keep it sorted assuming a is sorted.\n\
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\n\
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If x is already in a, insert it to the left of the leftmost x.\n\
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\n\
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Optional args lo (default 0) and hi (default len(a)) bound the\n\
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slice of a to be searched.\n");
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static PyMethodDef bisect_methods[] = {
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{"bisect_right", (PyCFunction)bisect_right,
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METH_VARARGS|METH_KEYWORDS, bisect_right_doc},
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{"bisect", (PyCFunction)bisect_right,
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METH_VARARGS|METH_KEYWORDS, bisect_right_doc},
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{"insort_right", (PyCFunction)insort_right,
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METH_VARARGS|METH_KEYWORDS, insort_right_doc},
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{"insort", (PyCFunction)insort_right,
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METH_VARARGS|METH_KEYWORDS, insort_right_doc},
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{"bisect_left", (PyCFunction)bisect_left,
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METH_VARARGS|METH_KEYWORDS, bisect_left_doc},
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{"insort_left", (PyCFunction)insort_left,
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METH_VARARGS|METH_KEYWORDS, insort_left_doc},
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{NULL, NULL} /* sentinel */
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};
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PyDoc_STRVAR(module_doc,
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"Bisection algorithms.\n\
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\n\
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This module provides support for maintaining a list in sorted order without\n\
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having to sort the list after each insertion. For long lists of items with\n\
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expensive comparison operations, this can be an improvement over the more\n\
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common approach.\n");
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PyMODINIT_FUNC
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init_bisect(void)
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{
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Py_InitModule3("_bisect", bisect_methods, module_doc);
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}
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