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 spec‐
ify 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 per‐
forms the same computation for single precision data.
These functions are not guaranteed to deliver results that are identi‐
cal to the results of evaluating 1.0 / sqrt(x) given the same argu‐
ments. 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 excep‐
tion 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 feclearex‐
cept(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 exam‐
ine 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(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Committed │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOsqrt(3M), feclearexcept(3M), fetestexcept(3M), attributes(5)SunOS 5.10 14 Dec 2007 vrsqrt_(3MVEC)
