Article View: comp.lang.fortran
Article #6530Re: Precision of floating point multiply
From: Robert Myers
Date: Mon, 29 Sep 2003 02:55
Date: Mon, 29 Sep 2003 02:55
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3084 bytes
On Sat, 27 Sep 2003 00:17:13 GMT, "Glen Herrmannsfeldt" <gah@ugcs.caltech.edu> wrote: <snip> > >PL/I has the MULTIPLY function where one can specify the desired result >precision. At least one compiler I know of expands both operands before >doing a double precision multiply when double precision is desired. > >If someone wanted to comment about other hardware or compilers in use in the >1960's and 1970's, that might also be useful. > When I took numerical methods as a graduate student (mid-seventies), I knew only PL/I and 360 Assembler. Everybody was running on IBM 360 (or whatever the model was at the time). My classmates, who all used Fortran IV (while I was coding in PL/I), invariably got different answers (in the least significant digits) doing the same problem on the same machine. Since I was not majoring in computer science, neither the professor nor I had the competence or the interest to explore the details, although I might take a different attitude today. I got my thesis written without ever learning Fortran, but my graduation into the world of employment put an end to my dogged loyalty to PL/I, a language I still miss. I'd like to propose the eccentric view that having little oddities of floating point arithmetic floating around isn't necessarily a bad thing. A rigidly enforced monoculture of floating point arithmetic could mask problems that otherwise might surface in a slightly less precise world. RM
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