Re: How to search in a file efficiently (=fast !) for a certain hex
value ?
Christian wrote:
John W. Kennedy schrieb:
Ulf Meinhardt wrote:
How can I efficiently (!) and fast search a file for a given hex
value (e.g. x'6A')
resp. how can I count the number of occurencies in a given hex value ?
java.nio.MappedByteBuffer
probably this will be even slower than just using an input Stream..
MappedByteBuffer may have some possibilitys for use.. but not for sth
like this.. secially if the file is too big... the os might have to
cache the file on another place of the disc..
It may be difficult to guarantee anything for something that is
so platform specific.
But common platforms should:
- map all the file into virtual memory
- only have some of it in physical memory
- read directly from the file with no use of pagefile or
other temp disk IO
to the op:
what is wrong with
BufferedInputStream bis = new BufferedInputStream(new
FileInputStream(file));
int read;
int[] timesRead = new int[256];
while (-1 != (read = bis.read()) {
timesRead[read & 0xff]++;
}
to read in the file..
it is simple, you won't get much faster and afterwards you can look up
the occurences easily ...
Even with BufferedInputStream I would go for multi byte read instead
of single byte read.
Arne