From: Matt Borland (matt_at_[hidden])
Date: 2025-02-01 19:41:36
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> John Maddock wrote:
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> > In late breaking news, I also hear from Matt that GCC and IBM both "cheat" by using (mutually incompatible) non-IEEE binary encodings.
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> Are these documented anywhere? It would be interesting to look at them for inspiration.
>
I wish. They docs just say BID format. Here is what IEEE 754 specifies:
https://github.com/cppalliance/decimal/blob/develop/include/boost/decimal/decimal32.hpp#L72-L102
Here is what I gathered from trying to wrap the builtin libstdc++ (IBM) types:
I kept dumping the bits of powers of two etc to figure it out:
Basically, it's laid out like a binary float most of the time. In Intel's case for implementation of mathematical functions they convert the Decimal32 to a float, perform an operation, and then convert back. Makes things pretty quick when your conversion operation is NOP, and then you can offload computations to presumably the MKL.
Matt