CMSIS DSP Software Library: Cosine Main Page Modules Data Structures Files Examples Functions | Variables Cosine [Fast Math Functions] Functions float32_t arm_cos_f32 (float32_t x) q31_t arm_cos_q31 (q31_t x) q15_t arm_cos_q15 (q15_t x) Variables static const float32_t cosTable [259] static const q31_t cosTableQ31 [259] static const q15_t cosTableQ15 [259] Detailed Description Computes the trigonometric cosine function using a combination of table lookup and cubic interpolation. There are separate functions for Q15, Q31, and floating-point data types. The input to the floating-point version is in radians while the fixed-point Q15 and Q31 have a scaled input with the range [0 1) mapping to [0 2*pi). The implementation is based on table lookup using 256 values together with cubic interpolation. The steps used are: Calculation of the nearest integer table index Fetch the four table values a, b, c, and d Compute the fractional portion (fract) of the table index. Calculation of wa, wb, wc, wd The final result equals a*wa + b*wb + c*wc + d*wd where a=Table[index-1]; b=Table[index+0]; c=Table[index+1]; d=Table[index+2]; and wa=-(1/6)*fract.^3 + (1/2)*fract.^2 - (1/3)*fract; wb=(1/2)*fract.^3 - fract.^2 - (1/2)*fract + 1; wc=-(1/2)*fract.^3+(1/2)*fract.^2+fract; wd=(1/6)*fract.^3 - (1/6)*fract; Function Documentation float32_t arm_cos_f32 ( float32_t  x ) Fast approximation to the trigonometric cosine function for floating-point data. Parameters: [in]xinput value in radians. Returns:cos(x). Examples: arm_sin_cos_example_f32.c. Definition at line 189 of file arm_cos_f32.c. q31_t arm_cos_q31 ( q31_t  x ) Fast approximation to the trigonometric cosine function for Q31 data. Parameters: [in]xScaled input value in radians. Returns:cos(x). The Q31 input value is in the range [0 +1) and is mapped to a radian value in the range [0 2*pi). Definition at line 133 of file arm_cos_q31.c. q15_t arm_cos_q15 ( q15_t  x ) Fast approximation to the trigonometric cosine function for Q15 data. Parameters: [in]xScaled input value in radians. Returns:cos(x). The Q15 input value is in the range [0 +1) and is mapped to a radian value in the range [0 2*pi). Definition at line 102 of file arm_cos_q15.c. Variable Documentation const float32_t cosTable[259] [static] Example code for Generation of Cos Table: tableSize = 256; for(n = -1; n < (tableSize + 1); n++) { cosTable[n+1]= cos(2*pi*n/tableSize); } where pi value is 3.14159265358979 Definition at line 83 of file arm_cos_f32.c. const q31_t cosTableQ31[259] [static] Table Values are in Q31(1.31 Fixed point format) and generation is done in three steps First Generate cos values in floating point: tableSize = 256; for(n = -1; n < (tableSize + 1); n++) { cosTable[n+1]= cos(2*pi*n/tableSize); } where pi value is 3.14159265358979 Secondly Convert Floating point to Q31(Fixed point): (cosTable[i] * pow(2, 31)) Finally Rounding to nearest integer is done cosTable[i] += (cosTable[i] > 0 ? 0.5 :-0.5); Definition at line 57 of file arm_cos_q31.c. const q15_t cosTableQ15[259] [static] Table Values are in Q15(1.15 Fixed point format) and generation is done in three steps First Generate cos values in floating point: tableSize = 256; for(n = -1; n < (tableSize + 1); n++) { cosTable[n+1]= cos(2*pi*n/tableSize); } where pi value is 3.14159265358979 Secondly Convert Floating point to Q15(Fixed point): round(cosTable[i] * pow(2, 15)) Finally Rounding to nearest integer is done cosTable[i] += (cosTable[i] > 0 ? 0.5 :-0.5); Definition at line 57 of file arm_cos_q15.c.  All Data Structures Files Functions Variables Typedefs Enumerations Enumerator Defines Generated on Mon Nov 29 2010 17:20:00 for CMSIS DSP Software Library by  1.7.2

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