Extracting ints from a unsigned long

ruby-talk
1

I have a bunch of binary data consisting of 4 ints stored inside an unsigned
long.

Here's psuedo C code to extract out the ints:

// data is a FILE pointer to the file
unsigned long temp;
fread(temp, sizeof(temp), 1, data);
int first = temp >> 24;
int second = temp << 8 >> 24;
int third = temp << 16 >> 24;
int fourth = temp << 24 >> 24;

I'm trying to do the same thing in Ruby, but I'm having difficulties with
the bitshifting. Any ideas? Would it make since to inline C code in Ruby
for this?

Joe

2

str = someio.read 16
first, second, third, fourth = str.unpack("l4")

···

On Fri, Nov 19, 2004 at 07:53:19AM +0900, Joe Van Dyk wrote:

I have a bunch of binary data consisting of 4 ints stored inside an unsigned
long.

Here's psuedo C code to extract out the ints:

// data is a FILE pointer to the file
unsigned long temp;
fread(temp, sizeof(temp), 1, data);
int first = temp >> 24;
int second = temp << 8 >> 24;
int third = temp << 16 >> 24;
int fourth = temp << 24 >> 24;

I'm trying to do the same thing in Ruby, but I'm having difficulties with
the bitshifting. Any ideas? Would it make since to inline C code in Ruby
for this?

--
Hassle-free packages for Ruby?
RPA is available from http://www.rubyarchive.org/

3

Joe Van Dyk wrote:

I have a bunch of binary data consisting of 4 ints stored inside an unsigned
long.

Here's psuedo C code to extract out the ints:

// data is a FILE pointer to the file
unsigned long temp;
fread(temp, sizeof(temp), 1, data);
int first = temp >> 24;
int second = temp << 8 >> 24;
int third = temp << 16 >> 24;
int fourth = temp << 24 >> 24;

I'm trying to do the same thing in Ruby, but I'm having difficulties with
the bitshifting. Any ideas? Would it make since to inline C code in Ruby
for this?

irb(main):003:0> [1,2,3,4].pack "C*"
=> "\001\002\003\004"
irb(main):004:0> [1,2,3,4].pack("C*").unpack("C*")
=> [1, 2, 3, 4]

4

Surely they must be 4 shorts ( 16bits ) to be stored inside one long ( 64bits )?

···

On Fri, 19 Nov 2004 07:53:19 +0900, Joe Van Dyk <joe.vandyk@boeing.com> wrote:

I have a bunch of binary data consisting of 4 ints stored inside an unsigned
long.

Here's psuedo C code to extract out the ints:

// data is a FILE pointer to the file
unsigned long temp;
fread(temp, sizeof(temp), 1, data);
int first = temp >> 24;
int second = temp << 8 >> 24;
int third = temp << 16 >> 24;
int fourth = temp << 24 >> 24;

I'm trying to do the same thing in Ruby, but I'm having difficulties with
the bitshifting. Any ideas? Would it make since to inline C code in Ruby
for this?

Joe

5

Or, starting with the unsigned long;

# pack('N') => network byte order;
# pack('V') => little-endian byte order
# pack('L') => native byte order
[123456789].pack('N').unpack('C*')
    ==>[7, 91, 205, 21]

ri unpack for more.

hth,
Mark

···

On Fri, 19 Nov 2004 08:05:21 +0900, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:

Joe Van Dyk wrote:

> I have a bunch of binary data consisting of 4 ints stored inside an unsigned
> long.
>
> Here's psuedo C code to extract out the ints:
>
> // data is a FILE pointer to the file
> unsigned long temp;
> fread(temp, sizeof(temp), 1, data);
> int first = temp >> 24;
> int second = temp << 8 >> 24;
> int third = temp << 16 >> 24;
> int fourth = temp << 24 >> 24;
>
>
> I'm trying to do the same thing in Ruby, but I'm having difficulties with
> the bitshifting. Any ideas? Would it make since to inline C code in Ruby
> for this?

irb(main):003:0> [1,2,3,4].pack "C*"
=> "\001\002\003\004"
irb(main):004:0> [1,2,3,4].pack("C*").unpack("C*")
=> [1, 2, 3, 4]

6

Joel VanderWerf wrote:

Joe Van Dyk wrote:

I have a bunch of binary data consisting of 4 ints
stored inside an unsigned long.

Here's psuedo C code to extract out the ints:

// data is a FILE pointer to the file
unsigned long temp;
fread(temp, sizeof(temp), 1, data);
int first = temp >> 24;
int second = temp << 8 >> 24;
int third = temp << 16 >> 24;
int fourth = temp << 24 >> 24;

I'm trying to do the same thing in Ruby, but I'm having
difficulties with the bitshifting. Any ideas? Would it
make since to inline C code in Ruby for this?

irb(main):003:0> [1,2,3,4].pack "C*"
=> "\001\002\003\004"
irb(main):004:0> [1,2,3,4].pack("C*").unpack("C*")
=> [1, 2, 3, 4]

Ah.... I didn't know that I needed to have the "C*" part. Thanks.

7

Joe Van Dyk wrote:

Joel VanderWerf wrote:

irb(main):003:0> [1,2,3,4].pack "C*"
=> "\001\002\003\004"
irb(main):004:0> [1,2,3,4].pack("C*").unpack("C*")
=> [1, 2, 3, 4]

Ah.... I didn't know that I needed to have the "C*" part. Thanks.

unpack("C4") will work too. You may want "c4" instead if you are using signed ints.