VRSQRT_(3MVEC) Vector Math Library Functions VRSQRT_(3MVEC)
NAME
vrsqrt_, vrsqrtf_ - vector reciprocal square root functions
SYNOPSIS
cc [
flag... ]
file...
-lmvec [
library... ]
void vrsqrt_(
int *n,
double * restrict x,
int *stridex,
double * restrict y,
int *stridey);
void vrsqrtf_(
int *n,
float * restrict x,
int *stridex,
float * restrict y,
int *stridey);
DESCRIPTION
These functions evaluate the function
rsqrt(
x), defined by
rsqrt(
x) =
1 /
sqrt(
x), for an entire vector of values at once. The first
parameter specifies the number of values to compute. Subsequent
parameters specify the argument and result vectors. Each vector is
described by a pointer to the first element and a stride, which is
the increment between successive elements.
Specifically,
vrsqrt_(
n,
x,
sx,
y,
sy) computes
y[
i * *
sy] =
rsqrt(
x[
i * *
sx]) for each
i = 0, 1, ..., *
n - 1. The
vrsqrtf_() function performs the same computation for single precision data.
These functions are not guaranteed to deliver results that are
identical to the results of evaluating 1.0 /
sqrt(
x) given the same
arguments. Non-exceptional results, however, are accurate to within
a unit in the last place.
USAGE
The element count *
n must be greater than zero. The strides for the
argument and result arrays can be arbitrary integers, but the arrays
themselves must not be the same or overlap. A zero stride effectively
collapses an entire vector into a single element. A negative stride
causes a vector to be accessed in descending memory order, but note
that the corresponding pointer must still point to the first element
of the vector to be used; if the stride is negative, this will be the
highest-addressed element in memory. This convention differs from the
Level 1 BLAS, in which array parameters always refer to the lowest-
addressed element in memory even when negative increments are used.
These functions assume that the default round-to-nearest rounding
direction mode is in effect. On x86, these functions also assume that
the default round-to-64-bit rounding precision mode is in effect. The
result of calling a vector function with a non-default rounding mode
in effect is undefined.
These functions handle special cases and exceptions in the spirit of
IEEE 754. In particular,
o if
x < 0,
rsqrt(
x) is NaN, and an invalid operation
exception is raised,
o
rsqrt(NaN) is NaN,
o
rsqrt(+Inf) is +0,
o
rsqrt(+-0) is +-Inf, and a division-by-zero exception is
raised.
An application wanting to check for exceptions should call
feclearexcept(
FE_ALL_EXCEPT) before calling these functions. On
return, if
fetestexcept(
FE_INVALID |
FE_DIVBYZERO |
FE_OVERFLOW |
FE_UNDERFLOW) is non-zero, an exception has been raised. The
application can then examine the result or argument vectors for
exceptional values. Some vector functions can raise the inexact
exception even if all elements of the argument array are such that
the numerical results are exact.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+----------------------------+-----------------------------+
|Interface Stability | Committed |
+----------------------------+-----------------------------+
|MT-Level | MT-Safe |
+----------------------------+-----------------------------+
SEE ALSO
feclearexcept(3M),
fetestexcept(3M),
sqrt(3M),
attributes(7)SunOS 5.11 December 14, 2007 VRSQRT_(3MVEC)
