Extended 80-bit hex floating point (IEEE?) conversion

Alex Tweedly alex at tweedly.net
Sat Feb 5 20:07:33 CST 2011


You could easily clean this code up.
You could easily make it much shorter and/or faster

I just ignored corner cases, error checking, and other cases that 
probably don't matter to you.
I just ignored negative numbers !!!

and with all those caveats, try this in your msg box

> put "400EAC44000000000000" into hexstring
>
> repeat with i = 1 to 20
>   if char i of hexstring is not a number then
>      put 10 + chartonum(char i of hexstring) - chartonum("A") into t
>      -- put char i of hexstring && t & CR after msg
>     put t into v[i]
>  else
>    put char i of hexstring into v[i]
> end if
> end repeat
>
>
> put 0 into t
> repeat with i=1 to 4
>   put t*16 + v[i] into t
>   -- put i && v[i] && t & CR after msg
> end repeat
> put t into texp
>
> put 0 into t
> repeat with i = 5 to 12
>   put t*16 + v[i] into t
> end repeat
> put t into mantissa
>
> put texp && mantissa && mantissa & CR after msg
> put texp - 16383 into texp
> put mantissa * 2^(texp-31) after msg

Oh, by the way, I also ignored the lower half of the mantissa - i.e. 
extra precision.
That probably doesn't matter for the kind of numbers you'll see for 
sample rates, etc.

-- Alex.

On 05/02/2011 03:01, stephen barncard wrote:
> Still messing with exporting sounds out of Livecode. Working with AIF
> files for now.
>
> I can't yet find where Livecode stores the metadata like length,
> sample rate and bit depth for imported sound files.
>
> In the meantime, I can grab these values from the incoming aif files
> and store them in custom properties ins the soundclip object.
>
> The aiff sample rate is defined in 10 hex bytes of Extended 80-bit
> floating point, like so: (big endian)
>
> 44100  =
>
> 40 0E AC 44 00 00 00 00 00 00<http://www.onicos.com/staff/iz/formats/ieee.c>
>
> 48000   =
>
> 40 0E BB 80 00 00 00 00 00 00<http://www.onicos.com/staff/iz/formats/ieee.c>
>
> 96000   =
>
> 40 0F BB 80 00 00 00 00 00 00
>   <http://www.onicos.com/staff/iz/formats/ieee.c>
>
> Extended 80-bit floating-point format
> <http://www.onicos.com/staff/iz/formats/ieee.c>
>
>
> I could use some help here.. I want to detect other sample rates. The ones
> above were determined by examining them in sound files with known rates.
>
> How would I convert these 80 bit hex floating point numbers to the values
> shown and back again?. Baseconvert doesn't work with this many hex
> characters. (linked is some C source...)
> surely this can be done in Livecode...
>
> thanks in advance...
>




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