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```HYPOT(3)                 BSD 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
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
general, 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).