• Walter Bright (2/2) May 23 2006 is now up on:
• Sean Kelly (9/12) May 23 2006 Great stuff! I've only read the first page so far, but one thing caught...
• Walter Bright (3/18) May 23 2006 Only about two dozen people reviewed that article, and all missed it
• James Mansion (7/8) Jun 01 2006 Hmm. vptr is typically not at offset 0 if the base class is a POD. It ...
• Sean Kelly (9/18) Jun 01 2006 The tricks are useful in other ways though. For example, I work with a
• Walter Bright (4/12) Jun 01 2006 You do have to check that the vptr is in the right place, and adjust

Walter Bright <newshound digitalmars.com> writes:

is now up on:

http://www.artima.com/cppsource/backyard.html

Sean Kelly <sean f4.ca> writes:

Walter Bright wrote:
 is now up on:
 
 http://www.artima.com/cppsource/backyard.html

Great stuff!  I've only read the first page so far, but one thing caught 
my eye.  Change:

"We can then define a dehydrated pointer as being odd, and a hydrated 
pointer as being 1."

to:

"We can then define a dehydrated pointer as being odd, and a hydrated 
pointer as being even."


Sean

Walter Bright <newshound digitalmars.com> writes:

Sean Kelly wrote:
 Walter Bright wrote:
 is now up on:

 http://www.artima.com/cppsource/backyard.html

 
 Great stuff!  I've only read the first page so far, but one thing caught 
 my eye.  Change:
 
 "We can then define a dehydrated pointer as being odd, and a hydrated 
 pointer as being 1."
 
 to:
 
 "We can then define a dehydrated pointer as being odd, and a hydrated 
 pointer as being even."

Only about two dozen people reviewed that article, and all missed it 
<g>. Thanks.

James Mansion <James_member pathlink.com> writes:

http://www.artima.com/cppsource/backyard.html

Hmm.  vptr is typically not at offset 0 if the base class is a POD.  It might
be, depending on whether the compiler decides to change 'this' on the cast to
base instead of just using an offset, but YMMV.

I can't help thinking that if you replace your malloc with nedmalloc or
PTMalloc3 then most people will get a bigger speed boost than they will by
trying to play dirty at such a low level.

James

Sean Kelly <sean f4.ca> writes:

James Mansion wrote:
 http://www.artima.com/cppsource/backyard.html

 
 Hmm.  vptr is typically not at offset 0 if the base class is a POD.  It might
 be, depending on whether the compiler decides to change 'this' on the cast to
 base instead of just using an offset, but YMMV.
 
 I can't help thinking that if you replace your malloc with nedmalloc or
 PTMalloc3 then most people will get a bigger speed boost than they will by
 trying to play dirty at such a low level.

The tricks are useful in other ways though.  For example, I work with a 
piece of software whose "database" is a memory mapped file containing 
objects with modified vtbls.  The result is screaming fast and isn't 
something that could be accomplished by other means.  So I view this 
article more as a window to some of the evil (and sometimes useful) 
games one can play with C++ than as a template one should follow to 
increase performance in a typical application.


Sean

Walter Bright <newshound digitalmars.com> writes:

James Mansion wrote:
 http://www.artima.com/cppsource/backyard.html

 
 Hmm.  vptr is typically not at offset 0 if the base class is a POD.  It might
 be, depending on whether the compiler decides to change 'this' on the cast to
 base instead of just using an offset, but YMMV.

You do have to check that the vptr is in the right place, and adjust 
accordingly.


 I can't help thinking that if you replace your malloc with nedmalloc or
 PTMalloc3 then most people will get a bigger speed boost than they will by
 trying to play dirty at such a low level.

Why not do both and get double the speedup?