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Re: Floating-point formats and standards
A couple of corrections to the 754R description:
Bradd W. Szonye wrote:
> New name Sig Exp Old name Currently implemented by
> binary16 11 5
> binary32 23 8 single all systems (hardware)
> binary64 52 11 double all systems (hardware)
> binary80 64 15 extended all x86-based systems (hardware)
> binary128 112 15 quad most RISC systems (software)
In the current draft, the extended format is called "binaryx" instead of
"binary80." Implementations are supposed to provide at least one high-
precision format for intermediate calculations, either binary128 (a
basic format) or binaryx (an implementation-defined format about 50%
more precise than its best basic format).
One proposal recommends specifying binaryx as the x86 extended format. I
have no way of knowing for certain, but I suspect that it will succeed,
since x86 and quad are the only /de facto/ standards for high-precision
IEEE 754 flonums.
That proposal also states which formats a system should support.
For high-performance technical systems:
Binary64 is mandatory for computation and storage.
Binary32 is recommended for low-precision, high-density storage.
Binaryx is recommended for computation on x86-compatible systems.
Binary128 is recommended for expression evaluation (i.e., temps).
For commercial and financial systems:
Decimal128 is mandatory for computation and storage.
Decimal32 and decimal64 are recommended for storage.
The binary requirements match reality pretty well, except for the
binary128 recommendation. (Currently, only x86 systems use high-
precision temps, and they use binaryx instead of binary128.)
Hope this helps.
Bradd W. Szonye