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Embedded Software and Motor Control Libraries for PXR40xx

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The computation algorithm <strong>for</strong> arcsin(x) uses the symmetry of the arcsin(x) function<br />

around the point (0, 0), which allows the calculation of the function values just in interval<br />

[0, 1), <strong>and</strong> to calculation of the function values in the interval [-1, 0), use the simple<br />

<strong>for</strong>mula:<br />

where:<br />

Equation GFLIB_Asin_Eq1<br />

• y[-1, 0) is the arcsin(x) function value in the interval [-1, 0)<br />

• y[0, 1] is the arcsin(x) function value in the interval [0, 1]<br />

For the interval [0, 0.4), the algorithm uses a Minimax approximation as follows:<br />

Equation GFLIB_Asin_Eq2<br />

For the interval [0.4, 1), the algorithm uses a polynomial approximation as follows.<br />

Equation GFLIB_Asin_Eq3<br />

To calculate the values of the arcsin(x) function in interval [-1, 0), the symmetry of the<br />

arcsin(x) function is used <strong>and</strong> the value is determined by the following <strong>for</strong>mula:<br />

Equation GFLIB_Asin_Eq4<br />

Chapter 4 API References<br />

Minimax approximation coefficients used <strong>for</strong> GFLIB_Asin_FLT calculation in interval<br />

[0, 0.4), are noted in Table 4-36.<br />

<strong>Embedded</strong> <strong>Software</strong> <strong>and</strong> <strong>Motor</strong> <strong>Control</strong> <strong>Libraries</strong> <strong>for</strong> <strong>PXR40xx</strong>, Rev. 1.0<br />

Freescale Semiconductor, Inc. 231

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