Embedded Software and Motor Control Libraries for PXR40xx

Figure 4-20 depicts a floating point arctangent function generated from Matlab and the
approximated value of the arctangent function obtained from GFLIB_Atan_F32, plus
their difference. The course of calculation accuracy as a function of the input value can
be observed from this figure. The achieved accuracy with consideration to the 3rd order
piece-wise minimax polynomial approximation and described fixed point scaling is less
than 0.5LSB on the upper 16 bits of the 32-bit result.
Note
The output angle is normalized into the range [-0.25, 0.25). The
function call is slightly different from common approach in the
library set. The function can be called in four different ways:
• With implementation postfix (i.e. GFLIB_Atan_F32(f32In,
&pParam)), where the &pParam is pointer to
approximation coefficients. In case the default
approximation coefficients are used, the &pParam must be
replaced with GFLIB_ATAN_DEFAULT_F32 symbol.
The &pParam parameter is mandatory.
• With additional implementation parameter (i.e.
GFLIB_Atan(f32In, &pParam, F32), where the &pParam is
pointer to approximation coefficients. In case the default
approximation coefficients are used, the &pParam must be
replaced with GFLIB_ATAN_DEFAULT_F32 symbol.
The &pParam parameter is mandatory.
• With preselected default implementation (i.e.
GFLIB_Atan(f32In, &pParam), where the &pParam is
pointer to approximation coefficients. The &pParam
parameter is optional and in case it is not used, the default
GFLIB_ATAN_DEFAULT_F32 approximation
coefficients are used.
4.31.5 Re-entrancy
The function is re-entrant.
4.31.6 Code Example
#include "gflib.h"
tFrac32 f32Input;
tFrac32 f32Angle;
void main(void)
Embedded Software and Motor Control Libraries for PXR40xx, Rev. 1.0
Chapter 4 API References
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