Sine Cosine

Variables
static const float32_t	cosTable [360]
static const float32_t	sinTable [360]
static const int32_t	sinTableQ31 [360]
static const int32_t	cosTableQ31 [360]
Functions
void	arm_sin_cos_f32 (float32_t theta, float32_t *pSinVal, float32_t *pCosVal)
	Floating-point sin_cos function.
void	arm_sin_cos_q31 (q31_t theta, q31_t *pSinVal, q31_t *pCosVal)
	Q31 sin_cos function.

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Description

Computes the trigonometric sine and cosine values using a combination of table lookup and linear interpolation. There are separate functions for Q31 and floating-point data types. The input to the floating-point version is in degrees while the fixed-point Q31 have a scaled input with the range [-1 0.9999] mapping to [-180 179] degrees.

The implementation is based on table lookup using 360 values together with linear interpolation. The steps used are:

1. Calculation of the nearest integer table index.
2. Compute the fractional portion (fract) of the input.
3. Fetch the value corresponding to index from sine table to y0 and also value from index+1 to y1.
4. Sine value is computed as *psinVal = y0 + (fract * (y1 - y0)).
5. Fetch the value corresponding to index from cosine table to y0 and also value from index+1 to y1.
6. Cosine value is computed as *pcosVal = y0 + (fract * (y1 - y0)).

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Variable Documentation

const float32_t cosTable[360] [static]

Cosine Table is generated from following loop

for(i = 0; i < 360; i++)    
 {    
    cosTable[i]= cos((i-180) * PI/180.0);    
 } 

Referenced by arm_sin_cos_f32().

const int32_t cosTableQ31[360] [static]

Cosine Table is generated from following loop

for(i = 0; i < 360; i++)    
 {    
    cosTable[i]= cos((i-180) * PI/180.0);    
 } 

Convert above coefficients to fixed point 1.31 format.

Referenced by arm_sin_cos_q31().

const float32_t sinTable[360] [static]

Sine Table is generated from following loop

for(i = 0; i < 360; i++)    
 {    
    sinTable[i]= sin((i-180) * PI/180.0);    
 } 

Referenced by arm_sin_cos_f32().

const int32_t sinTableQ31[360] [static]

Sine Table is generated from following loop

for(i = 0; i < 360; i++)    
 {    
    sinTable[i]= sin((i-180) * PI/180.0);    
 } 

Convert above coefficients to fixed point 1.31 format.

Referenced by arm_sin_cos_q31().

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Function Documentation

void arm_sin_cos_f32	(	float32_t	theta,
		float32_t *	pSinVal,
		float32_t *	pCosVal
	)

Parameters:

[in]	theta	input value in degrees
[out]	*pSinVal	points to the processed sine output.
[out]	*pCosVal	points to the processed cos output.

Returns:

none.

References cosTable, and sinTable.

void arm_sin_cos_q31	(	q31_t	theta,
		q31_t *	pSinVal,
		q31_t *	pCosVal
	)

Parameters:

[in]	theta	scaled input value in degrees
[out]	*pSinVal	points to the processed sine output.
[out]	*pCosVal	points to the processed cosine output.

Returns:

none.

The Q31 input value is in the range [-1 0.999999] and is mapped to a degree value in the range [-180 179].

References cosTableQ31, INPUT_SPACING, and sinTableQ31.