From: Seth Willits <[EMAIL PROTECTED]>
Date: Sat, 11 Feb 2006 00:28:26 -0800
If you're reading from a file and appending to a string a lot and
this string is going to grow pretty large, your application can
benefit significantly if you preallocate a block of memory and resize
it only when needed. With strings, each time you assign to a string
you're going to be reallocating a chunk of memory for the string. If
you cut down the allocations to one or just a handful, it can speed
up things significantly.
I wrote a very small quick class called CapacityString to show this
and a quick demo app to test it.
For a 1.7 MB file, reading in 2 KB chunks with a BinaryStream a
standard loop like that below takes about 8.5 seconds.
for i = 1 to length step 2048
s = s + bin.Read(2048)
next
Now by comparison, using a CapacityString, I can read a 27 MB file
and it takes 0.15 seconds. No joke.
My ElfData plugin could probably do the same thing in half the time.
I'd actually guess that reading things in 64KB chunks is faster than
2KB chunks, though, but that applies to both approaches.
With my ElfData plugin you'd do this:
dim fs as new FastString
const ChunkSize = 64*1024
for i = 1 to length step ChunkSize
fs.AppendString bin.Read(ChunkSize)
next
In addition .AppendString, the FastString class has a ton of useful
functions for creating text or data files. http://www.elfdata.com/
plugin/technicalref/FastString.html
For example, you can append one byte many times (useful for creating
neatly formatted printouts where you might want to align text into
columns). It can append UTF8 character codes. It can append integers
as hex, or integers as text.
I've got one example where .AppendIntegerAsText runs about 22X faster
than RB could manage even if your CapacityString were as fast as my
FastString class. (which it is not).
I've tested my FastString against a class by Charles Yeomans. I got
this result:
Longest test took: 33.9s
Bytes Per Append=7
Append Count = 100
RB = 1x
ED = 3x
CY = 0.99x
Append Count = 1100
RB = 1x
ED = 14.5x
CY = 2.8x
Append Count = 2100
RB = 1x
ED = 24.7x
CY = 4.02x
Append Count = 3100
RB = 1x
ED = 151x
CY = 30.6x
Append Count = 4100
RB = 1x
ED = 280x
CY = 54.4x
Append Count = 5100
RB = 1x
ED = 408x
CY = 70.8x
Append Count = 6100
RB = 1x
ED = 513x
CY = 87.9x
Append Count = 7100
RB = 1x
ED = 618x
CY = 109x
Append Count = 8100
RB = 1x
ED = 710x
CY = 123x
Append Count = 9100
RB = 1x
ED = 756x
CY = 135x
In addition to being having many useful functions, and being very
fast, my FastString class has a long history of being used for almost
everything. I've made it very easy to use, and added "the little
things" that make using it much easier.
It is a mature class.
For example .FreeSize property can be set, as well as the .Size
and .Length properties. These are convenient to set sometimes. I
often will reduce .Length by 1 byte after a loop that added a number
and then a space, to remove the final space. Reducing .Length doesn't
take up any noticable time.
My plugin is also free for non-commercial use and is available for
Mac, Win32, and Linux.
--
http://elfdata.com/plugin/
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