Le 21/12/2012 11:46, phil_shvarcz a écrit :
Hi all,
being new to scilab I'm not sure if my problem has a trivial solution or
not. I searched all documentation and forum postings but did not find
anything relevant for my problem. So that's it:
I need to read in quite big binary files (several 100MB) composed of
successive pairs of float (4 byte word) and double (8 byte word). That is,
the byte sequence looks like this ("ffff" is a 4-byte float and "dddddddd"
is an 8 byte double):
ffffddddddddffffddddddddffffddddddddffffdddddd
if I use this code:
You forgot it?
the file is read in at an incredibly slow rate (a few MB take minutes to be
read in).
If I read in the entire file in one flush
it takes a second or so to read in 100MB. However, the data structure is
lost and the vector vb contains nonsensical doubles.
Is there a way in scilab to read in a (structureless) vector of bytes and
cast it to the right structure afterwards, like one would do with an array
in C ?
I do not think so.
Besides, is it normal that mread is *so* slow when used to read a file in a
word-by-word manner instead of reading it in one big chunk?
I do not know the mread function. Whre do you find it?
Any way it is normal that a word_by-word read being slower because on
each iteration the program as to check if the arguments are ok or not,
the system as to create an interrupt , ...
May be you can use a code similar to the one below to be able to read
your file. It is bit tricky because it needs to create an intermediate file
suppose your file is named yourfile and contains N floatting point numbers
//read all the numbers in the file assumming float format
u=mopen('yourfile','r');
T=mget(3*N,'f',u);
F=T(1:3:$); // the float numbers
mclose(u);
//now write down all the records corresponding to doubles
I=(2:3)'.*.ones(1,N/2)+(0:3:3*N-3).*.ones(2,1);
u=mopen('/tmp/foo','w')
mput(T(I),'f',u);
mclose(u);
//read it again as double
u=mopen('/tmp/foo','r');
D=mget(N,'d',u);
mclose(u);
Serge Steer
Thanks for reading,
regards
Phil
--
View this message in context:
http://mailinglists.scilab.org/Performance-issue-with-mget-on-inhomogeneous-binary-file-tp4025574.html
Sent from the Scilab users - Mailing Lists Archives mailing list archive at
Nabble.com.
_______________________________________________
users mailing list
[email protected]
http://lists.scilab.org/mailman/listinfo/users
_______________________________________________
users mailing list
[email protected]
http://lists.scilab.org/mailman/listinfo/users
