HYPOT(3)

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

LIBRARY
libm

SYNOPSIS
#include <math.h>
double
hypot(double x, double y);
float
hypotf(float x, float y);
#include <complex.h>
double
cabs(double complex z);
float
cabsf(float complex z);

DESCRIPTION
The hypot() and hypotf() 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. The cabs() and cabsf() functions compute the complex absolute value of z.

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

ERROR (due to Roundoff, etc.)
Below 0.97 ulps. Consequently hypot(5.0, 12.0) = 13.0 exactly; in general, 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, ) and hypot(, v) are for all finite v. But programmers might be surprised at first to discover that hypot(±, ) = +. 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 is designed to disappear when it turns out to be irrelevant, as it does in hypot(, ).

SEE ALSO
math(3), sqrt(3)

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