On 3/31/11 12:58 PM, Alexander Belopolsky wrote:
On Thu, Mar 31, 2011 at 12:36 PM, Robert Kern<robert.kern@gmail.com> wrote: ..
The proposed letter code is 'e', as used in numpy. I'm not sure of the logic that went behind the choice, except perhaps that 'e' is near 'd' and 'f'.
So it is 'e' for half, 'f' for single and 'd' for double. Given that in English alphabet the order is d, e, f, I find this choice rather unintuitive.
It's not too late to change, though. I don't know of any other group that has decided on such any kind of letter code for half-floats.
There is a language, Q, that uses "e" for single-precision floats. They call C-float "real" and C-double "float". See <http://www.kx.com/q/d/primer.htm>. Codes "e" for binary32 and "f" for binary64 make some sense alphabetically, but would suggest "d" for binary16, which would neither work for Python nor for Q because "d" is double in Python and date in Q.
Note that IEEE 754-2008 also defines a binary128, quadruple precision format. If we keep assigning single letter codes to datatypes, struct/buffer format will soon resemble strftime with every letter of English alphabet having some (often non-obvious) meaning.
Oh, we're well down that path. :-)
(If we have to choose a single-letter code, I would vote for 'a' for hAlf and 'u' for qUad.)
'u' is already reserved in PEP 3118, and 'a' is already used in numpy, though not in the PEP 3118 interface implementation.
I would rather see some syntax that would allow multi-character type specifications. For example, {binary16} for half-floats and {binary128} for quadruple precision floats. This syntax may allow for support 3rd party type registry and private extensions.
PEP 3118 does define a parametric 't' type: 16t would be a 16-bit field with undefined internal format. Elsewhere in the thread I suggested an extension to this add a freeform name to this type to allow 3rd parties agree on new types without needing changes to PEP 3118 or needing more single-letter codes. E.g. 16t{halffloat} -> IEEE 754-2008 half-float 128t{quadfloat} -> IEEE 754-2008 quad-float 96t{80bitfloat} -> 80-bit extended precision float stored in 96 bits etc. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco