DragonFly On-Line Manual Pages
HYPOT(3) DragonFly Library Functions Manual HYPOT(3)
hypot, hypotf, hypotl, cabs, cabsf, cabsl -- Euclidean distance and com-
plex absolute value functions
hypot(double x, double y);
hypotf(float x, float y);
hypotl(long double x, long double y);
cabs(double complex z);
cabsf(float complex z);
cabsl(long double complex z);
The hypot(), hypotf() and hypotl() 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
The cabs(), cabsf() and cabsl() functions return the absolute value of
the complex number z.
ERRORS (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
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 infin-
ity) 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).
A hypot() function first appeared in Version 3 AT&T UNIX, and cabs() in
Version 7 AT&T UNIX.
DragonFly 5.1 January 15, 2015 DragonFly 5.1