while (($n = read FILE, $buffer, 4))
 {
 
 $decimal = unpack("N", pack("B32", $buffer));
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$buffer gets a four byte (32 bit) binary string read from the file and then you convert that with pack("B32", $buffer)???   That pack is not doing what you seem to think it is doing.   You just need the unpack:

 $decimal = unpack 'N', $buffer;
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