hypot (3)
Leading comments
Copyright 1993 David Metcalfe (david@prism.demon.co.uk) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Sin...
NAME
hypot, hypotf, hypotl  Euclidean distance functionSYNOPSIS
#include <math.h> double hypot(double x, double y);
float hypotf(float x, float y);
long double hypotl(long double x, long double y);
Link with lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
hypot():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or cc std=c99
hypotf(), hypotl():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 600  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or cc std=c99
DESCRIPTION
These functions return sqrt(x*x+y*y). This is the length of the hypotenuse of a rightangled triangle with sides of length x and y, or the distance of the point (x,y) from the origin.The calculation is performed without undue overflow or underflow during the intermediate steps of the calculation.
RETURN VALUE
On success, these functions return the length of a rightangled triangle with sides of length x and y.If x or y is an infinity, positive infinity is returned.
If x or y is a NaN, and the other argument is not an infinity, a NaN is returned.
If the result overflows, a range error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively.
If both arguments are subnormal, and the result is subnormal, a range error occurs, and the correct result is returned.
ERRORS
See math_error(7) for information on how to determine whether an error has occurred when calling these functions.The following errors can occur:
 Range error: result overflow
 errno is set to ERANGE. An overflow floatingpoint exception (FE_OVERFLOW) is raised.
 Range error: result underflow
 An underflow floatingpoint exception (FE_UNDERFLOW) is raised.
 These functions do not set errno for this case.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).Interface  Attribute  Value 
hypot(), hypotf(), hypotl()  Thread safety  MTSafe 
CONFORMING TO
C99, POSIX.12001, POSIX.12008.The variant returning double also conforms to SVr4, 4.3BSD.