hypot man page on 4.4BSD

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HYPOT(3)		 BSD Library Functions Manual		      HYPOT(3)

NAME
     hypot, cabs — euclidean distance and complex absolute value functions

SYNOPSIS
     #include <math.h>

     double
     hypot(double x, double y);

     struct {double x, y;} z;

     double
     cabs(z);

DESCRIPTION
     The hypot() and cabs() functions computes the sqrt(x*x+y*y) in such a way
     that underflow will not happen, and overflow occurs only if the final
     result deserves it.

     hypot(∞, v) = hypot(v, ∞) = +∞ for all v, including NaN.

ERROR (due to Roundoff, etc.)
     Below 0.97 ulps.  Consequently hypot(5.0, 12.0) = 13.0 exactly; in gen‐
     eral, hypot and cabs return an integer whenever an integer might be
     expected.

     The same cannot be said for the shorter and faster version of hypot and
     cabs that is provided in the comments in cabs.c; its error can exceed 1.2
     ulps.

NOTES
     As might be expected, hypot(v, NaN) and hypot(NaN, v) are NaN for all
     finite v; with "reserved operand" in place of "NaN", the same is true on
     a VAX.  But programmers on machines other than a VAX (if has no ∞) might
     be surprised at first to discover that hypot(±∞, NaN) = +∞.  This is
     intentional; it happens because hypot(∞, v) = +∞ for all v, finite or
     infinite.	Hence hypot(∞, v) is independent of v.	Unlike the reserved
     operand fault on a VAX, the IEEE NaN is designed to disappear when it
     turns out to be irrelevant, as it does in hypot(∞, NaN).

SEE ALSO
     math(3), sqrt(3)

HISTORY
     Both a hypot() function and a cabs() function appeared in Version 7 AT&T
     UNIX.

4th Berkeley Distribution	 June 4, 1993	     4th Berkeley Distribution
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