Bitwise Shift Porting from PHP

ruby-talk
1

I am trying to port the OLE Reader from PHP to read Excel files on any platform. I am stuck on the following function:

function GetInt4d($data, $pos) {
   return ord($data[$pos]) | (ord($data[$pos+1]) << 8) | \
   (ord($data[$pos+2]) << 16) | (ord($data[$pos+3]) << 24);
}

My ruby version is:

def get_int_4_d(data, pos)
   (data[pos]) | ((data[pos+1]) << 8) | \
   ((data[pos+2]) << 16) | ((data[pos+3]) << 24)
end

It works in some cases but in the example xls file I am using, when data[pos,0] is the character þ, the function returns -2 in PHP and 4294967294 in Ruby.

Thanks for your help.

Dan

2

your php function should have been named

   GetSignedInt

and your ruby function should be named

   get_unsigned_int_4_d

remember, 2 ** 32 => 4294967296. for larger numbers your php function wraps
and yields negative numbers - dunno if it's supposed to. you should look at
String#unpack. assuming you want to unpack a signed int in lsb order from
data starting at pos your method would become

   def get_int_4_d(data, pos)
     data[pos,4].unpack('i').first
   end

although you should be sure to understand little/big endian issues with regard
to your data and these functions.

hth.

-a

···

On Mon, 18 Jul 2005, Dan Fitzpatrick wrote:

I am trying to port the OLE Reader from PHP to read Excel files on any platform. I am stuck on the following function:

function GetInt4d($data, $pos) {
return ord($data[$pos]) | (ord($data[$pos+1]) << 8) | \
(ord($data[$pos+2]) << 16) | (ord($data[$pos+3]) << 24);
}

My ruby version is:

def get_int_4_d(data, pos)
(data[pos]) | ((data[pos+1]) << 8) | \
((data[pos+2]) << 16) | ((data[pos+3]) << 24)
end

It works in some cases but in the example xls file I am using, when data[pos,0] is the character þ, the function returns -2 in PHP and 4294967294 in Ruby.

Thanks for your help.

--

email :: ara [dot] t [dot] howard [at] noaa [dot] gov
phone :: 303.497.6469
My religion is very simple. My religion is kindness.
--Tenzin Gyatso

===============================================================================

3

Ara.T.Howard wrote:

···

On Mon, 18 Jul 2005, Dan Fitzpatrick wrote:

I am trying to port the OLE Reader from PHP to read Excel files on any platform. I am stuck on the following function:

function GetInt4d($data, $pos) {
return ord($data[$pos]) | (ord($data[$pos+1]) << 8) | \
(ord($data[$pos+2]) << 16) | (ord($data[$pos+3]) << 24);
}

My ruby version is:

def get_int_4_d(data, pos)
(data[pos]) | ((data[pos+1]) << 8) | \
((data[pos+2]) << 16) | ((data[pos+3]) << 24)
end

It works in some cases but in the example xls file I am using, when data[pos,0] is the character �, the function returns -2 in PHP and 4294967294 in Ruby.

Thanks for your help.

your php function should have been named

  GetSignedInt

and your ruby function should be named

  get_unsigned_int_4_d

remember, 2 ** 32 => 4294967296. for larger numbers your php function wraps
and yields negative numbers - dunno if it's supposed to. you should look at
String#unpack. assuming you want to unpack a signed int in lsb order from
data starting at pos your method would become

  def get_int_4_d(data, pos)
    data[pos,4].unpack('i').first
  end

although you should be sure to understand little/big endian issues with regard
to your data and these functions.

hth.

-a

Ara,

Thanks. That works great. I will look into endian info. Don't know anything about it yet.

Dan