sqrt.3

早期freebsd实现

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.\"     @(#)sqrt.3	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt SQRT 3
.Os
.Sh NAME
.Nm cbrt ,
.Nm sqrt
.Nd cube root and square root functions
.Sh SYNOPSIS
.Fd #include <math.h>
.Ft double
.Fn cbrt "double x"
.Ft double
.Fn sqrt "double x"
.Sh DESCRIPTION
The
.Fn cbrt
function computes
the cube root of
.Ar x .
.Pp
The
.Fn sqrt
computes the
non-negative square root of x.
.Sh RETURN VALUES
The
.Fn cbrt
function returns the requested cube root.
The
.Fn sqrt
function returns the requested square root
unless an error occurs.
On the
.Tn VAX
or
.Tn Tahoe
processor an attempt to take the
.Fn sqrt
of negative
.Fa x
causes an error; in this event,
the global variable
.Va errno
is set to
.Dv EDOM
and a reserved operand fault is generated.
.Sh ERROR (due to Roundoff etc.)
The
.Fn cbrt
function
is accurate to within 0.7
.Em ulps .
.Pp
The
.Fn sqrt
function on a
.Tn VAX
is accurate to within 0.501
.Em ulps .
Sqrt on a machine that conforms to
.Tn IEEE
754 is correctly rounded
in accordance with the rounding mode in force; the error is less than
half an
.Em ulp
in the default mode (round\-to\-nearest).
An
.Em ulp
is one
.Em U Ns nit
in the
.Em L Ns ast
.Em P Ns lace
carried.
.Sh SEE ALSO
.Xr math 3 ,
.Xr infnan 3
.Sh STANDARDS
The
.Nm sqrt
function conforms to
.St -ansiC .
.Sh HISTORY
The
.Nm cbrt
function appeared in
.Bx 4.3 .