PHP - How do I convert a 6byte string storing a 48bit floating point to a number in PHP?

Question

AMOS supports a 48-bit floating point format consisting of a 40-bit mantissa, 8-bit exponent, and a signbit.
Because a normalized mantissa always starts with a binary one in the high-order bit, this bit is not
stored in the floating point number but is always assumed to be present. This allows us to represent the
40-bit mantissa in only 39 bits.

http://www.alphamicroproducts.com/dsm00/04010A00.pdf

chapter 11 for more details on how the floating point number is stored.

Answer 1

Try this:

$number = unpack('f', $six_byte_string);

For more information, see:

http://www.php.net/unpack

Answer 2

You probably need to convert it to an IEEE 64-bit floating point (double) by bit-shifting. I don't know how you do this in PHP - if you discover it isn't possible you can write an external program (e.g. in C) to do the conversion for you.

Populate a stream with the bits of the 6-byte string, inserting the required bits to pad it to a 64-bit float. Then read in the stream to a double as if you were reading it from a new file.

Answer 3

sorry