[Mono-bugs] [Bug 68723][Nor] Changed - Performance on long arith

bugzilla-daemon@bugzilla.ximian.com bugzilla-daemon@bugzilla.ximian.com
Mon, 25 Oct 2004 09:44:01 -0400 (EDT)

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Changed by lupus@ximian.com.


--- shadow/68723	2004-10-24 23:46:35.000000000 -0400
+++ shadow/68723.tmp.23270	2004-10-25 09:44:01.000000000 -0400
@@ -129,6 +129,15 @@
 The problem here is that the long ops are an icall, so that we can use
 the gcc generated code. We could manually write the code for division
 and multiplication and have the jit know about it.
 Good luck on your exam.
+------- Additional Comments From lupus@ximian.com  2004-10-25 09:44 -------
+O(n) algorithms are expected to be faster than O(log n) only for
+large values of n. In practice the constants may have a large impact
+on the runtime. Professors often don't tell you about this fundamental
+detail, possibly because few of them actually write code.
+The main issue here is that we don't optimize division and modulus by
+power of two on longs and the helper functions are called through the
+icall wrapper which does increase the constant overhead.