From: Dan Fitzpatrick <dan@...>
Date: 2005-07-18T23:37:28+09:00
Subject: Re: Bitwise Shift Porting from PHP

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