cabs(3) - NetBSD Manual Pages

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HYPOT(3)                NetBSD Library Functions Manual               HYPOT(3)


NAME

     hypot, hypotf, cabs, cabsf -- Euclidean distance and complex absolute
     value functions


LIBRARY

     Math Library (libm, -lm)


SYNOPSIS

     #include <math.h>

     double
     hypot(double x, double y);

     float
     hypotf(float x, float y);

     double
     cabs(struct complex { double x; double y; } z);

     float
     cabsf(struct complex { float x; float y; } z);


DESCRIPTION

     The hypot() and cabs() functions compute 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(infinity, v) = hypot(v, infinity) = +infinity for all v, including
     NaN.


ERRORS

     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 (it has no infinity)
     might be surprised at first to discover that hypot(±infinity, NaN) =
     +infinity.  This is intentional; it happens because hypot(infinity, v) =
     +infinity for all v, finite or infinite.  Hence hypot(infinity, 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(infinity, NaN).


SEE ALSO

     math(3), sqrt(3)


HISTORY

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


BUGS

     The cabs() and cabsf() functions use structures that are not defined in
     any header and need to be defined by the user.  As such they cannot be
     prototyped properly.

NetBSD 3.1                        May 6, 1991                       NetBSD 3.1