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Re: [Scheme-reports] EQV? on numbers should be based on operational equivalence
| Date: Wed, 9 May 2012 00:03:05 -0400
| From: John Cowan <cowan@x>
| Ray Dillinger scripsit:
| > A high-level language such as scheme ought to treat values as
| > values according to their types, not as bit layouts. Control
| > over bit layouts should be purely for external purposes;
| > reading/writing binary formats and interfacing with ABI's.
| Well then, either binary files and FFIs cannot be standardized, or
| we have to admit that there are boundaries to "operational
| equivalence". I go with the latter viewpoint.
The SLIB byte-number module (using byte and logical modules)
converts (both directions) between byte-vectors and IEEE
floating-point numbers using only R4RS arithmetic procedures. It can
produce either endianness; default is big-endian. The endianess it
uses is completely independent of the native CPU endianess.
Because it cannot "see" bits within NaN, it uses a single bit-pattern
for the byte-vector representation of NaN. A NaN converted from a
byte-vector uses whichever NaN results from dividing 0.0 by 0.0 on the
Access to hardware representations of numbers is not needed for
portably "reading/writing binary formats". The SLIB "pnm" module
(using other modules) can read and write binary pbm, pgm, and ppm
files using only R4RS.
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