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Embedded Software and Motor Control Libraries for PXR40xx

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Function GFLIB_Acos_FLT<br />

Figure 4-11. Course of the function GFLIB_Acos<br />

The computation algorithm <strong>for</strong> arccos(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 calculate the function values in the interval [-1, 0) use the simple <strong>for</strong>mula:<br />

where:<br />

Equation GFLIB_Acos_Eq1<br />

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

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

For the interval [0, 1 ], the algorithm uses a polynomial approximation as follows:<br />

Equation GFLIB_Acos_Eq2<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_Acos_Eq3<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 />

218 Freescale Semiconductor, Inc.

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