On Thu, 2007-02-15 at 19:23 +0200, Peter wrote: > On Thu, 15 Feb 2007, Gilboa Davara wrote: > > > Small example. > > About two years ago I go bored, and decided to implement binary trees in > > (x86) Assembly. > > The end result was between 2-10 times faster then GCC (-O2/-O3) > > generated code. (Depending the size of the tree) > > The main reason being the lack of a 3 way comparison in C. > > (above/below/equal) > > And assembly lacks it too.
????????!!!? cmp $eax,$ebx jb label_below ja label_above <equal code> > But in C you can get creative with compound > statements: > int x,y; > register int t; > > (t = x - y) && (((t < 0) && below()) || above()) || equal(); .. Which will only work if the below/above/equal are made of short statements which is a very problematic pre-requisite. In my case I needed to store some additional information in each leaf - making each step a compound statement by itself. (which in-turn, rendered your compound less effective) > which wastes 1 register variable. Still, there is no guarantee that this > generates faster code than an optimizing compiler (and gcc is not known > among the best optimizing compilers). Rewriting above using binary > operators and masks may be even faster. The same code was also tested under Visual Studio 2K3 and showed the same results. The assembly code was considerably faster then the VS generate binary. > > Atomic code execution should not require assembly because segment > locking can be done using C (even if that C is inline assembly for > some applications). A. I -was- talking about in-line assembly. B. How can I implement "lock btX/inc/dec/sub/add" in pure C? (Let alone using the resulting flags. [setXX]) BTW, another valid excuse to using assembly (at least in register-barren-world-known-as-i386) is the ability to trash the base pointer. (every register count.) - Gilboa ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
