# SIMD.%type%.reciprocalSqrtApproximation()

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SIMD.js has been taken out of active development in TC39 and removed from Stage 3. It is not being pursued by web browsers for implementation anymore. SIMD operations exposed to the web are under active development within WebAssembly, with operations based on the SIMD.js operations.

The static `SIMD.%type%.reciprocalSqrtApproximation()` method returns a new instance with an approximation of the reciprocal value (`1 / x`) of the square root (`Math.sqrt()`) of the lane values.

## Syntax

```SIMD.Float32x4.reciprocalSqrtApproximation(t)
SIMD.Float64x2.reciprocalSqrtApproximation(t)```

### Parameters

t
An instance of a corresponding SIMD type.

### Return value

A new corresponding SIMD data type with the reciprocal (`1 / x`) of the square root (`Math.sqrt()`) of the values.

## Description

The `SIMD.%type%.reciprocalSqrtApproximation()` is an approximation of the reciprocal of the square root of the lane values. This means that an estimation of the reciprocal of a number is calculated and that there can be a small amount of error. The Newton-Raphson division, for example, is one of the fast division methods that calculates an estimation. See also this ARM/NEON FAQ article.

## Examples

```var a = SIMD.Float32x4(1, 2, 3, 4);
SIMD.Float32x4.reciprocalSqrtApproximation(a);
// Float32x4[1, 0.7071067690849304, 0.5773502588272095, 0.5]

var b = SIMD.Float64x2(0, Infinity);
SIMD.Float64x2.reciprocalSqrtApproximation(b);
// Float64x2[Infinity, 0]
```

## Specifications

Specification Status Comment
SIMD
The definition of 'SIMDConstructor.reciprocalSqrtApproximation' in that specification.
Obsolete Initial definition.

## Browser compatibility

Experimental SIMD.js has been removed from browsers. It's still available in Firefox Nightly, but will be removed in favor of a SIMD implementation in WebAssembly. See also bug 1416723.