bpo-24700: Add a fast path for comparing array.array of equal type (#3009)

Author: adrian17

Lib/test/test_array.py

@@ -1342,6 +1342,16 @@ class FPTest(NumberTest):
     def assertEntryEqual(self, entry1, entry2):
         self.assertAlmostEqual(entry1, entry2)
 
+    def test_nan(self):
+        a = array.array(self.typecode, [float('nan')])
+        b = array.array(self.typecode, [float('nan')])
+        self.assertIs(a != b, True)
+        self.assertIs(a == b, False)
+        self.assertIs(a > b, False)
+        self.assertIs(a >= b, False)
+        self.assertIs(a < b, False)
+        self.assertIs(a <= b, False)
+
     def test_byteswap(self):
         a = array.array(self.typecode, self.example)
         self.assertRaises(TypeError, a.byteswap, 42)

Misc/NEWS.d/next/Library/2017-08-08-15-14-34.bpo-24700.44mvNV.rst

@@ -0,0 +1,2 @@
+Optimize array.array comparison. It is now from 10x up to 70x faster when
+comparing arrays holding values of the same integer type.

Modules/arraymodule.c

@@ -31,6 +31,7 @@ struct arraydescr {
     int itemsize;
     PyObject * (*getitem)(struct arrayobject *, Py_ssize_t);
     int (*setitem)(struct arrayobject *, Py_ssize_t, PyObject *);
+    int (*compareitems)(const void *, const void *, Py_ssize_t);
     const char *formats;
     int is_integer_type;
     int is_signed;
@@ -518,26 +519,48 @@ d_setitem(arrayobject *ap, Py_ssize_t i, PyObject *v)
     return 0;
 }
 
+#define DEFINE_COMPAREITEMS(code, type) \
+    static int \
+    code##_compareitems(const void *lhs, const void *rhs, Py_ssize_t length) \
+    { \
+        const type *a = lhs, *b = rhs; \
+        for (Py_ssize_t i = 0; i < length; ++i) \
+            if (a[i] != b[i]) \
+                return a[i] < b[i] ? -1 : 1; \
+        return 0; \
+    }
+
+DEFINE_COMPAREITEMS(b, signed char)
+DEFINE_COMPAREITEMS(BB, unsigned char)
+DEFINE_COMPAREITEMS(u, Py_UNICODE)
+DEFINE_COMPAREITEMS(h, short)
+DEFINE_COMPAREITEMS(HH, unsigned short)
+DEFINE_COMPAREITEMS(i, int)
+DEFINE_COMPAREITEMS(II, unsigned int)
+DEFINE_COMPAREITEMS(l, long)
+DEFINE_COMPAREITEMS(LL, unsigned long)
+DEFINE_COMPAREITEMS(q, long long)
+DEFINE_COMPAREITEMS(QQ, unsigned long long)
 
 /* Description of types.
  *
  * Don't forget to update typecode_to_mformat_code() if you add a new
  * typecode.
  */
 static const struct arraydescr descriptors[] = {
-    {'b', 1, b_getitem, b_setitem, "b", 1, 1},
-    {'B', 1, BB_getitem, BB_setitem, "B", 1, 0},
-    {'u', sizeof(Py_UNICODE), u_getitem, u_setitem, "u", 0, 0},
-    {'h', sizeof(short), h_getitem, h_setitem, "h", 1, 1},
-    {'H', sizeof(short), HH_getitem, HH_setitem, "H", 1, 0},
-    {'i', sizeof(int), i_getitem, i_setitem, "i", 1, 1},
-    {'I', sizeof(int), II_getitem, II_setitem, "I", 1, 0},
-    {'l', sizeof(long), l_getitem, l_setitem, "l", 1, 1},
-    {'L', sizeof(long), LL_getitem, LL_setitem, "L", 1, 0},
-    {'q', sizeof(long long), q_getitem, q_setitem, "q", 1, 1},
-    {'Q', sizeof(long long), QQ_getitem, QQ_setitem, "Q", 1, 0},
-    {'f', sizeof(float), f_getitem, f_setitem, "f", 0, 0},
-    {'d', sizeof(double), d_getitem, d_setitem, "d", 0, 0},
+    {'b', 1, b_getitem, b_setitem, b_compareitems, "b", 1, 1},
+    {'B', 1, BB_getitem, BB_setitem, BB_compareitems, "B", 1, 0},
+    {'u', sizeof(Py_UNICODE), u_getitem, u_setitem, u_compareitems, "u", 0, 0},
+    {'h', sizeof(short), h_getitem, h_setitem, h_compareitems, "h", 1, 1},
+    {'H', sizeof(short), HH_getitem, HH_setitem, HH_compareitems, "H", 1, 0},
+    {'i', sizeof(int), i_getitem, i_setitem, i_compareitems, "i", 1, 1},
+    {'I', sizeof(int), II_getitem, II_setitem, II_compareitems, "I", 1, 0},
+    {'l', sizeof(long), l_getitem, l_setitem, l_compareitems, "l", 1, 1},
+    {'L', sizeof(long), LL_getitem, LL_setitem, LL_compareitems, "L", 1, 0},
+    {'q', sizeof(long long), q_getitem, q_setitem, q_compareitems, "q", 1, 1},
+    {'Q', sizeof(long long), QQ_getitem, QQ_setitem, QQ_compareitems, "Q", 1, 0},
+    {'f', sizeof(float), f_getitem, f_setitem, NULL, "f", 0, 0},
+    {'d', sizeof(double), d_getitem, d_setitem, NULL, "d", 0, 0},
     {'\0', 0, 0, 0, 0, 0, 0} /* Sentinel */
 };
 
@@ -664,6 +687,31 @@ array_richcompare(PyObject *v, PyObject *w, int op)
         return res;
     }
 
+    if (va->ob_descr == wa->ob_descr && va->ob_descr->compareitems != NULL) {
+        /* Fast path:
+           arrays with same types can have their buffers compared directly */
+        Py_ssize_t common_length = Py_MIN(Py_SIZE(va), Py_SIZE(wa));
+        int result = va->ob_descr->compareitems(va->ob_item, wa->ob_item,
+                                                common_length);
+        if (result == 0)
+            goto compare_sizes;
+
+        int cmp;
+        switch (op) {
+        case Py_LT: cmp = result < 0; break;
+        case Py_LE: cmp = result <= 0; break;
+        case Py_EQ: cmp = result == 0; break;
+        case Py_NE: cmp = result != 0; break;
+        case Py_GT: cmp = result > 0; break;
+        case Py_GE: cmp = result >= 0; break;
+        default: return NULL; /* cannot happen */
+        }
+        PyObject *res = cmp ? Py_True : Py_False;
+        Py_INCREF(res);
+        return res;
+    }
+
+
     /* Search for the first index where items are different */
     k = 1;
     for (i = 0; i < Py_SIZE(va) && i < Py_SIZE(wa); i++) {
@@ -685,14 +733,17 @@ array_richcompare(PyObject *v, PyObject *w, int op)
 
     if (k) {
         /* No more items to compare -- compare sizes */
+        compare_sizes: ;
         Py_ssize_t vs = Py_SIZE(va);
         Py_ssize_t ws = Py_SIZE(wa);
         int cmp;
         switch (op) {
         case Py_LT: cmp = vs <  ws; break;
         case Py_LE: cmp = vs <= ws; break;
-        case Py_EQ: cmp = vs == ws; break;
-        case Py_NE: cmp = vs != ws; break;
+        /* If the lengths were not equal,
+           the earlier fast-path check would have caught that. */
+        case Py_EQ: assert(vs == ws); cmp = 1; break;
+        case Py_NE: assert(vs == ws); cmp = 0; break;
         case Py_GT: cmp = vs >  ws; break;
         case Py_GE: cmp = vs >= ws; break;
         default: return NULL; /* cannot happen */