Re^2: Unpacking extended-double precision floats

Howdy!

I'm reading a binary file. Part of the file consists of 10-byte sequences that are clearly floats, probably IEEE extended-double-precision floats. I'm looking to be able to convert to unpack that to a numeric value and pack it to a 10-byte sequence.

That is, unpack 0x4001c888888888888888 to 12.5 (if I'm remembering actual data correctly), and pack 12.5 back to 0x4001c888888888888888.

I may just resort to picking the bits apart and converting it myself. I'm not sure if my C compiler (gcc on Mac) does that particular datatype. I can afford to simply do the bit-slinging myself, if it comes to that. I was just hoping to find that someone else has already solved the problem. So far, no joy.

update: added more words to clarify

yours,
Michael

Comment on Re^2: Unpacking extended-double precision floats

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Re^3: Unpacking extended-double precision floats by ikegami (Patriarch) on Nov 29, 2006 at 18:43 UTC
My question was about 12.5's format. You implied (in a private message) that the lost of precision is of no concern, so I'm deducing that you want an NV (double). Have you tried `unpack 'D'` yet?	[reply] [d/l]
Re^4: Unpacking extended-double precision floats by Anonymous Monk on Nov 29, 2006 at 20:31 UTC
If loss of precision is of no concern, and the number of bits of exponent and sign is the same between d and D formats, you may be able to use unpack d plus two skip bytes, and pack it as a double d followed by two appropriate fill bytes (00 or 88 ?). Bill N1VUX	[reply]
Re^5: Unpacking extended-double precision floats by herveus (Prior) on Nov 30, 2006 at 12:35 UTC
Howdy! If I recall correctly (and I'll be checking the references before I do anything), "double precision" and "extended double precision" have different numbers of bits in the exponent. It's not quite that simple to smush the precision down. I think I go from 64 bits of mantissa to 53 bits of mantissa (but don't hold me to precise numbers here). In the end, I should be able to pick the three components apart and Just Do The Math. yours, Michael	[reply]
Re^6: Unpacking extended-double precision floats by Fengor (Pilgrim) on Nov 30, 2006 at 13:08 UTC
Re^7: Unpacking extended-double precision floats by BrowserUk (Patriarch) on Nov 30, 2006 at 13:28 UTC
Re^7: Unpacking extended-double precision floats by herveus (Prior) on Nov 30, 2006 at 13:29 UTC
Re^4: Unpacking extended-double precision floats by herveus (Prior) on Nov 29, 2006 at 18:48 UTC
Howdy! Yep. I tried that. The Perl on my mac (where I'm actually doing this) told me to pound sand. I'll try Convert::Binary::C when I get home. ...so, yes, I want an NV on the Perl side of things. yours, Michael	[reply]