1. Supercharge your peek_string()
Platform: Windows
No more hunting character by character
through memory for that notorious
zero string terminator
This new way of peek'ing a zstring is typically
at least 5 times faster then the old way, and its
only one line of code
--first link to this windows function any way you see fit:
xlstrlen=link_c_func(kernel32,"lstrlen",{C_POINTER},C_INT)
--then the new Euphoria function becomes:
function peek_zstring(atom lpzString)
return peek({lpzString,c_func(xlstrlen,{lpzString})})
end function
That's it!
I've named it "peek_zstring" to distinguish it from the old
function "peek_string", but more importantly to draw attention
to the importance of using it ONLY on zero terminated strings.
The speed increase should be REALLY drastic for very long
strings.
--typical usage:
atom lpFilename
sequence teststring
lpFilename=allocate_string("c:\\program files\\thisdir\\filename.txt")
teststring=peek_zstring(lpFilename)
printf(1,"%s\n",{teststring})
free(lpFilename)
On this particular string it benchmarked about 5 times faster
then a minimum form of the old peek_string().
Good luck with it!
--Al
2. Re: Supercharge your peek_string()
--- Al Getz <Xaxo at aol.com> wrote:
> This new way of peek'ing a zstring is typically
> at least 5 times faster then the old way, and its
> only one line of code
This is a lot like BSTR's, which are unicode strings (see my EuCOM stuff).
Actually, the number of bytes are stored in the four bytes before the pointer
to the string.
=====
Matt Lewis
http://www14.brinkster.com/matthewlewis
3. Re: Supercharge your peek_string()
Al,
I've incorporated your peek_string idea into win32lib. Thanks for the idea.
It works fast because I suspect it's written in optimized assembler.
I have no idea what Matt is on about. These strings are just byte arrays
that are terminated with a #00 byte.
Just try this experiment...
atom addr
integer len1, len2
addr = allocate(100)
poke(addr, "abcdefghijklmnopqrstuvwxyz" & 0)
len1 = c_func(xlstrlen, {addr})
len2 = c_func(xlstrlen, {addr + 1})
-- len2 --> 25
-- len1 --> 26
------
Derek Parnell
Melbourne, Australia
"To finish a job quickly, go slower."
4. Re: Supercharge your peek_string()
Matt is refering to the BSTR string type which is used in Visual Basic--it
has the string length as a 4-byte integer prefixed to the string itself and
NO terminating 0. VB uses these exclusively in its internal operations and
has functions to convert to or from zero-terminated strings for interacting
with the Windows API.
-- Mike Nelson, VB programmer (for cash), Eu programmer (for love)
