hypot(3) - NetBSD Manual Pages

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


NAME

     hypot, hypotf -- 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);


DESCRIPTION

     The hypot() functions compute the sqrt(x*x+y*y) in such a way that under-
     flow 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 returns an integer whenever an integer might be expected.

     The same cannot be said for the shorter and faster version of hypot 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.  cabs() was removed from public namespace in NetBSD 5.0 to avoid
     conflicts with the complex function in C99.

NetBSD 5.1.2                   February 12, 2007                  NetBSD 5.1.2