Changes between Version 2 and Version 3 of PossibleOptimizationAreas/ReduceDiscussion

Timestamp:

03/08/06 20:48:49 (7 years ago)

Author:

sasha

Comment:

Compare with Numeric

PossibleOptimizationAreas/ReduceDiscussion

@@ -6 +6 @@
 > python -m timeit -s "from numpy import zeros; x = zeros((2,500),'f')" "x[0]+x[1]"
 100000 loops, best of 3: 4.88 usec per loop
+}}}
+As Travis explained, some overhead is expected because {{{x.sum(0)}}} calls DOUBLE_add 500 times instead of 1 for {{{x[0]+x[1]}}}, but in Numeric 24.1 overhead was much smaller:
+{{{
+> python -m timeit -s "from Numeric import zeros,sum; x = zeros((2,500),'f')" "sum(x)"
+100000 loops, best of 3: 6.05 usec per loop
+> python -m timeit -s "from Numeric import zeros,sum; x = zeros((2,500),'f')" "x[0]+x[1]"
+100000 loops, best of 3: 3.63 usec per loop
+}}}
 
+Numeric 24.1 inner loop (ufuncobject.c:613-627):
+{{{
+    /* This is the inner loop to actually do the computation. */
+    loop=-1;
+    while(1) {
+        while (loop < n_loops-2) {
+            loop++;
+            loop_i[loop] = 0;
+            for(i=0; i<self->nin+self->nout; i++) { resets[loop][i] = pointers[i]; }
+        }
+
+        function(pointers, loop_n+(n_loops-1), steps[n_loops-1], data);
+
+        while (loop >= 0 && !(++loop_i[loop] < loop_n[loop]) && loop >= 0) loop--;
+        if (loop < 0) break;
+        for(i=0; i<self->nin+self->nout; i++) { pointers[i] = resets[loop][i] + steps[loop][i]*loop_i[loop]; }
+    }
 }}}
+
+Numpy r2208 inner loop  (ufuncobject.c:1968-1985):
+{{{
+                while(loop->index < loop->size) { 
+                        /* Copy first element to output */ 
+                        if (loop->obj)  
+                                Py_INCREF(*((PyObject **)loop->it->dataptr)); 
+                        memmove(loop->bufptr[1], loop->it->dataptr,  
+                               loop->outsize); 
+                        /* Adjust input pointer */ 
+                        loop->bufptr[0] = loop->it->dataptr+loop->steps[0]; 
+                        loop->function((char **)loop->bufptr,  
+                                       &(loop->N), 
+                                       loop->steps, loop->funcdata); 
+                        UFUNC_CHECK_ERROR(loop); 
+ 
+                        PyArray_ITER_NEXT(loop->it) 
+                        loop->bufptr[1] += loop->outsize; 
+                        loop->bufptr[2] = loop->bufptr[1]; 
+                        loop->index++;  
+                } 
+}}}