CMSIS-DSP  Verison 1.1.0
CMSIS DSP Software Library
Complex FFT Tables

Variables

const uint16_t armBitRevTable [1024]
const float32_t twiddleCoef [6144]
const q31_t twiddleCoefQ31 [6144]
const q15_t ALIGN4 twiddleCoefQ15 [6144]

Variable Documentation

const uint16_t armBitRevTable[1024]
Pseudo code for Generation of Bit reversal Table is
for(l=1;l <= N/4;l++)    
 {    
   for(i=0;i<logN2;i++)    
   {     
     a[i]=l&(1<<i);    
   }    
   for(j=0; j<logN2; j++)    
   {    
     if (a[j]!=0)    
     y[l]+=(1<<((logN2-1)-j));    
   }    
   y[l] = y[l] >> 1;    
  } 
where N = 4096 logN2 = 12
N is the maximum FFT Size supported

Referenced by arm_cfft_radix2_init_f32(), arm_cfft_radix2_init_q15(), arm_cfft_radix2_init_q31(), arm_cfft_radix4_init_f32(), arm_cfft_radix4_init_q15(), and arm_cfft_radix4_init_q31().

const float32_t twiddleCoef[6144]
Example code for Floating-point Twiddle factors Generation:
for(i = 0; i< 3N/4; i++)    
 {    
	twiddleCoef[2*i]= cos(i * 2*PI/(float)N);    
	twiddleCoef[2*i+1]= sin(i * 2*PI/(float)N);    
 } 
where N = 4096 and PI = 3.14159265358979
Cos and Sin values are in interleaved fashion

Referenced by arm_cfft_radix2_init_f32(), and arm_cfft_radix4_init_f32().

const q15_t ALIGN4 twiddleCoefQ15[6144]
Example code for Q15 Twiddle factors Generation::
for(i = 0; i< 3N/4; i++)    
 {    
	twiddleCoefQ15[2*i]= cos(i * 2*PI/(float)N);    
	twiddleCoefQ15[2*i+1]= sin(i * 2*PI/(float)N);    
 } 
where N = 4096 and PI = 3.14159265358979
Cos and Sin values are interleaved fashion
Convert Floating point to Q15(Fixed point 1.15): round(twiddleCoefQ15(i) * pow(2, 15))

Referenced by arm_cfft_radix2_init_q15(), and arm_cfft_radix4_init_q15().

const q31_t twiddleCoefQ31[6144]
Example code for Q31 Twiddle factors Generation::
for(i = 0; i< 3N/4; i++)    
 {    
    twiddleCoefQ31[2*i]= cos(i * 2*PI/(float)N);    
    twiddleCoefQ31[2*i+1]= sin(i * 2*PI/(float)N);    
 } 
where N = 4096 and PI = 3.14159265358979
Cos and Sin values are interleaved fashion
Convert Floating point to Q31(Fixed point 1.31): round(twiddleCoefQ31(i) * pow(2, 31))

Referenced by arm_cfft_radix2_init_q31(), and arm_cfft_radix4_init_q31().