Hi all,
I'm parsing a binary file, and need to read an integer, something I
would do in C like this:
int b;
read(f, &b, sizeof(int));
obviously considering endianness. I'm pretty sure there has to be a
faster way to do it, but this is how I'm doing it right now (as you
can see, pretty naive):
class IO
# read int, assume little endian
def geti
c1 = getc
c2 = getc
c3 = getc
c4 = getc
c4 << 3*8 | c3 << 2*8 | c2 << 8 | c1
end
end
What would be the ruby-way to do it?
thanks for any tip...
···
--
rolando -- [[ knowledge is empty, fill it ]] --
"Tam pro papa quam pro rege bibunt omnes sine lege."
class IO
def geti( endian = :little )
str = self.read( 4 )
str = str.reverse if endian == :little
str.unpack( 'N' )[0]
end
end
The default for this method is to return the integer in little endian
byte order. You can change this by passing :big as an argument ...
io.geti :big
It does not have to be :big, but I'm just following the metaphor of
using :little for little endian byte order.
Blessings,
TwP
···
On 10/12/06, Rolando Abarca <funkaster@gmail.com> wrote:
Hi all,
I'm parsing a binary file, and need to read an integer, something I
would do in C like this:
int b;
read(f, &b, sizeof(int));
obviously considering endianness. I'm pretty sure there has to be a
faster way to do it, but this is how I'm doing it right now (as you
can see, pretty naive):
class IO
# read int, assume little endian
def geti
c1 = getc
c2 = getc
c3 = getc
c4 = getc
c4 << 3*8 | c3 << 2*8 | c2 << 8 | c1
end
end
What would be the ruby-way to do it?
thanks for any tip...
no, but in my case works just fine. it will always be a 4 byte unsigned integer.
Kalman
regards,
···
On 10/12/06, Kalman Noel <invalid@gmx.net> wrote:
--
rolando -- [[ knowledge is empty, fill it ]] --
"Tam pro papa quam pro rege bibunt omnes sine lege."
No, we've just been parsing very large pixel images. No complex data
structures. Read four bytes, mask off the hamming code and error
bits, store the pixel data in an mmap cache, repeat until EOF.
From the bit-struct readme ...
"BitStruct is most efficient when your data is primarily treated as a
binary string, and only secondarily treated as a data structure. (For
instance, you are routing packets from one socket to another, possibly
looking at one or two fields as it passes through or munging some
headers.) If accessor operations are a bottleneck, a better approach
is to define a class that wraps an array and uses pack/unpack when the
object needs to behave like a binary string."
TwP
···
On 10/12/06, ara.t.howard@noaa.gov <ara.t.howard@noaa.gov> wrote:
On Fri, 13 Oct 2006, Tim Pease wrote:
>
> No problem. Take a look at bit-struct if you find yourself needing to
> do some more complex packing and unpacking of binary data ...
>
> http://raa.ruby-lang.org/project/bit-struct/
>
> Blessings,
> TwP
I thought that 'N' was _always_ a 32-bit in network byte order?
According to the docs, platform independent sizes are used everywhere
except the SsIiLl directives when escaped by an underscore...?
···
On Sat, 2006-10-14 at 02:42 +0900, Tim Pease wrote:
On 10/13/06, Robert Klemme <shortcutter@googlemail.com> wrote:
> On 12.10.2006 18:10, Kalman Noel wrote:
>
> class IO
> def geti( endian = :little )
> str = read( [0].pack('N').length )
> str.reverse! if endian == :little
> str.unpack( 'N' )[0]
> end
> end
>
Ooooo ... clever!
class IO
SIZEOF_INT = [0].pack('N').length
def geti( endian = :little )
str = read( SIZEOF_INT )
str.reverse! if endian == :little
str.unpack( 'N' )[0]
end
end
have you looked into using narray? then you can mask the entire image at
once. i have code that turns an mmap into an narray - it's quite simple. got
a sample file?
-a
···
On Fri, 13 Oct 2006, Tim Pease wrote:
On 10/12/06, ara.t.howard@noaa.gov <ara.t.howard@noaa.gov> wrote:
On Fri, 13 Oct 2006, Tim Pease wrote:
>
> No problem. Take a look at bit-struct if you find yourself needing to
> do some more complex packing and unpacking of binary data ...
>
> http://raa.ruby-lang.org/project/bit-struct/
>
> Blessings,
> TwP
have you been using this for your stuff tim?
No, we've just been parsing very large pixel images. No complex data
structures. Read four bytes, mask off the hamming code and error
bits, store the pixel data in an mmap cache, repeat until EOF.
--
my religion is very simple. my religion is kindness. -- the dalai lama
