rowley@ORVILLE.ARPA (Karl Rowley) (06/17/87)
The reason why MWC chose the VAX floating-point format has been questioned. VAX double-precision format is identical to single-precision format, except that the mantissa is extended. The IEEE format does not have this property. A floating-point library to use the VAX format is simplified by this similarity. In addition, all function arguments of type float are converted to doubles before they are put on the stack in MWC. Conversion from floats to doubles and back is certainly simple enough in VAX format. In other words, implementing the VAX floating-point format in software is probably simpler than implementing the IEEE format in software. Of course, IEEE format is superior in many ways, and doesn't have its bytes all flipped around. Karl Rowley rowley@orville.nas.nasa.gov
manis@ubc-cs.UUCP (06/19/87)
In article <8706171715.AA08471@orville.arpa> rowley@ORVILLE.ARPA.UUCP (Karl Rowley) writes: >VAX double-precision format is identical to single-precision format, except >that the mantissa is extended. The IEEE format does not have this property. Actually (not really being an expert in these matters) I believe that what MWC uses is the old PDP-11 format. VAXen nowadays have 4 (!) formats, of which MWC appears to use F (single) and D (old double) precision. Not having the VAX G format (less than double, but with more exponent bits) is something of a lose, in that one gets possibly more precision, but no more range. Since I rarely use floating point, I don't care that much. However, not having the same format as used by other ST languages is a bit of an annoyance, as is the inability to support coprocessors. >Of course, IEEE format is superior in many ways, and doesn't have its bytes >all flipped around. They could have done *much* worse. The 370 has its own floating point format. ----- Vincent Manis {seismo,uw-beaver}!ubc-vision!ubc-cs!manis Dept. of Computer Science manis@cs.ubc.cdn Univ. of British Columbia manis%ubc.csnet@csnet-relay.arpa Vancouver, B.C. V6T 1W5 manis@ubc.csnet (604) 228-6770 or 228-3061 "To lose one parent, Mr Worthing, may be regarded as a misfortune; but to lose both looks like carelessness." -- Oscar Wilde