Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!rice!sun-spots-request
From: neil@teleos.com (Neil Hunt)
Newsgroups: comp.sys.sun
Subject: <math.h>: what are _REDUCE() and _POLY()
Keywords: SunOS
Message-ID: <3643@kalliope.rice.edu>
Date: 2 Jun 89 17:47:13 GMT
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X-Sun-Spots-Digest: Volume 8, Issue 13, message 6 of 17

Looking in the file /usr/include/math.h, I found macros _POLYn and
_REDUCE.  While _POLYn is quite obvious (it appears to evaluate a
polynomial of order n whose coefficients are stored in an array), the
intended function of reduce is more opaque.  Can anyone shed any light?
Where are these macros used?

/*	@(#)math.h 1.2 86/10/07 SMI; from S5R2 2.5	*/
 ...
#define _REDUCE(TYPE, X, XN, C1, C2)	{ \
	double x1 = (double)(TYPE)X, x2 = X - x1; \
	X = x1 - (XN) * (C1); X += x2; X -= (XN) * (C2); }
 ...
#define _POLY1(x, c)	((c)[0] * (x) + (c)[1])
#define _POLY2(x, c)	(_POLY1((x), (c)) * (x) + (c)[2])
 ...
#define _POLY9(x, c)	(_POLY8((x), (c)) * (x) + (c)[9])

Neil/.

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