Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!purdue!mentor.cc.purdue.edu!l.cc.purdue.edu!cik From: cik@l.cc.purdue.edu (Herman Rubin) Newsgroups: comp.arch Subject: Re: hardware complex arithmetic support Summary: Exponents may be quite different. Message-ID: <1516@l.cc.purdue.edu> Date: 19 Aug 89 11:46:38 GMT References: <1672@crdgw1.crd.ge.com> <1549@convex.UUCP> Organization: Purdue University Statistics Department Lines: 28 In article <1549@convex.UUCP>, swarren@eugene.uucp (Steve Warren) writes: > In article <1758@crdgw1.crd.ge.com> davidsen@crdos1.UUCP(bill davidsen) writes: < < Could you 'splain this to me? It sounds as if you are saying that if < > Think of it as a vector. Changing the mantissa of the component that is > orders of magnitude smaller is not going to move the vector significantly. > > For example, if the magnitude of the smaller (call it V1) of the two > components is less than the least significant bit of the larger component > (call it V2), then the truncation error introduced by V2 is greater than > the error introduced by eliminating V1 entirely. V1 therefore should be > truncated at the least significant position in V2. There are situations, like computing FTs (fast or slow) where this is the case. There are other situations where this is not the case. I needed the complex error function with good relative error in both the real and imaginary parts for the case in which the real part of the argument was small. It was necessary for me to develop new algorithms to accomplish this; the existing algorithms with good relative error were quite poor at this. -- Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907 Phone: (317)494-6054 hrubin@l.cc.purdue.edu (Internet, bitnet, UUCP)