ruby / php operator differences.

[Aaron Smith]

I am trying to do some parsing of binary data.

Here is the psuedo code that parses what i'm looking for:
private int readInteger() throws IOException {
int n = 0;
int b = in.readUnsignedByte();
int result = 0;

while ((b & 0x80) != 0 && n < 3) {
result <<= 7;
result |= (b & 0x7f);
b = in.readUnsignedByte();
n++;
}
if (n < 3) {
result <<= 7;
result |= b;
} else {
/* Use all 8 bits from the 4th byte */
result <<= 8;
result |= b;

/* Check if the integer should be negative */
if ((result & 0x10000000) != 0) {
/* and extend the sign bit */
result |= 0xe0000000;
}
}

return result;
}




Here is how I wrote it with Ruby:
def read_int
n = 0;
b = @input_stream.read_special(1,'C')
result = 0

while((b & 0x80) != 0 && n < 3)
result <<= 7
result |= (b & 0x7f)
b = @input_stream.read_special(1,'C')
n = n + 1
end
if (n < 3)
result <<= 7
result |= b
else
# Use all 8 bits from the 4th byte
result <<= 8
result |= b

#Check if the integer should be negative
if ((result & 0x10000000) != 0)
# and extend the sign bit
result |= 0xe0000000
end
end

STDOUT.puts "READ INT: #{result}"
return result
end


When translating the Pseudo Code to PHP, it's verbatim except for
syntax. With ruby, I think i've found the problem with it not parsing
correclty. the |= operator. With PHP

$i |= 0xe0000000; //= -536870912

Now with Ruby:
i |= 0xe000000 #= true

Any ideas on a solution?

thanks.

 

[Brian Candler]

When translating the Pseudo Code to PHP, it's verbatim except for
syntax. With ruby, I think i've found the problem with it not parsing
correclty. the |= operator. With PHP

$i |= 0xe0000000; //= -536870912

Now with Ruby:
i |= 0xe000000 #= true

Errm, how about providing some evidence for that claim?

irb(main):010:0> 5 | 3
=> 7
irb(main):011:0> i = 0
=> 0
irb(main):012:0> i |= 0xe000000
=> 234881024

 

[Aaron Smith]

i wasn't 'claiming' anything. I was asking about why that was happening.
I figured it out though.

 

[Aaron Smith]

Hey Matz

I ended up writing the method a bit different,

int = @input_stream.read_special(1,'C')

if(int < 128)
STDOUT.puts "READ INT: #{int}"
return int
else
int = (int & 0x7f) << 7
tmp = @input_stream.read_special(1,'C')
if(tmp < 128)
STDOUT.puts "READ INT: #{int}"
return int | tmp
else
int = (int | (tmp & 0x7f)) << 7
tmp = @input_stream.read_special(1,'C')
if(tmp < 128)
STDOUT.puts "READ INT: #{int}"
return int | tmp
else
int = (int | (tmp & 0x7f)) << 8
tmp = @input_stream.read_special(1,'C')
int |= tmp

#Check if the integer should be negative
if ((int & 0x10000000) != 0)
## and extend the sign bit
int |= 0xe0000000
end
STDOUT.puts "READ INT: #{int}"
int
end
end
end


this seems to be working fine.

 

[Aaron Smith]

would it make sense that in php:
$int |= 0x10000000
is just shorthand for
$int = $int | 0x10000000

 

[Brian Candler]

would it make sense that in php:
$int |= 0x10000000
is just shorthand for
$int = $int | 0x10000000

It's the same in Ruby, except it goes further:

int |= 0x10000000

is short for

int = int | 0x10000000

is short for

int = int.|(0x10000000) # infix operator is really method call on LHS

is short for

int = int.send|, 0x10000000) # explicit method call by symbolic name

 

[Aaron Smith]

It's the same in Ruby, except it goes further:

int |= 0x10000000

is short for

int = int | 0x10000000

is short for

int = int.|(0x10000000) # infix operator is really method call on
LHS

is short for

int = int.send|, 0x10000000) # explicit method call by symbolic name

pretty flippin cool.

in this example:
int = int.send|,0x1000000)

is it neccessary to have assignment portion? as in:
int.send|,0x1000000), does this take out the need for (int=)

 

[Brian Candler]

pretty flippin cool.

in this example:
int = int.send|,0x1000000)

is it neccessary to have assignment portion? as in:
int.send|,0x1000000), does this take out the need for (int=)

You don't need to make use of the return value. Every expression in Ruby
returns a value, but you can simply ignore it.

In your particular example, if you write

int = 4
int.send|, 0x10000000)

it's valid Ruby but isn't very useful, as it calculates a result and then
throws it away. But many methods do have side effects:

str = "hello"
str.sendconcat, " world")
puts str

Actually you'd normally write the middle line as

str.concat(" world")

or

str.concat " world"

or

str << " world"

(since the << infix operator expands to a << method call on str, and for
Strings the << method does the same as concat)

This stems from the fact that a String in Ruby is a mutable object (it can
change). Most objects are. However a few objects, in particular numbers and
symbols, are immutable. That is, you can't send a message to the number 5
telling it to change its value

Regards,

Brian.

 

[Aaron Smith]

.................

Ah, yes that makes sense. Thanks.