ttrftech/NanoVNA
1
0
Fork 0
mirror of https://github.com/ttrftech/NanoVNA.git synced 2025-12-06 03:31:59 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity

Use compact variant sin_cos table in fft (not decrease speed, and need only 208 bytes flash)

Browse source
This commit is contained in:
DiSlord 2020-03-23 15:10:01 +03:00
parent 9221ad04ca
commit 48e28f79d0
1 changed files with 20 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

25
fft.h
View file

@ -26,6 +26,8 @@
#include <math.h>
#include <stdint.h>
// Use table increase transform speed from 6500 tick to 2025, increase code size on 700 bytes
// Use compact table, increase code size on 208 bytes, and not decrease speed
#define FFT_USE_SIN_COS_TABLE
static uint16_t reverse_bits(uint16_t x, int n) {
@ -43,6 +45,7 @@ static const float sin_table[] = {
printf("% .8f,%c", sin(2 * M_PI * i / FFT_SIZE), i % 8 == 7 ? '\n' : ' ');
}
*/
// for FFT_SIZE = 256
0.00000000, 0.02454123, 0.04906767, 0.07356456, 0.09801714, 0.12241068, 0.14673047, 0.17096189,
0.19509032, 0.21910124, 0.24298018, 0.26671276, 0.29028468, 0.31368174, 0.33688985, 0.35989504,
0.38268343, 0.40524131, 0.42755509, 0.44961133, 0.47139674, 0.49289819, 0.51410274, 0.53499762,
@ -51,7 +54,7 @@ static const float sin_table[] = {
0.83146961, 0.84485357, 0.85772861, 0.87008699, 0.88192126, 0.89322430, 0.90398929, 0.91420976,
0.92387953, 0.93299280, 0.94154407, 0.94952818, 0.95694034, 0.96377607, 0.97003125, 0.97570213,
0.98078528, 0.98527764, 0.98917651, 0.99247953, 0.99518473, 0.99729046, 0.99879546, 0.99969882,
1.00000000, 0.99969882, 0.99879546, 0.99729046, 0.99518473, 0.99247953, 0.98917651, 0.98527764,
1.00000000,/* 0.99969882, 0.99879546, 0.99729046, 0.99518473, 0.99247953, 0.98917651, 0.98527764,
0.98078528, 0.97570213, 0.97003125, 0.96377607, 0.95694034, 0.94952818, 0.94154407, 0.93299280,
0.92387953, 0.91420976, 0.90398929, 0.89322430, 0.88192126, 0.87008699, 0.85772861, 0.84485357,
0.83146961, 0.81758481, 0.80320753, 0.78834643, 0.77301045, 0.75720885, 0.74095113, 0.72424708,
@ -66,9 +69,19 @@ static const float sin_table[] = {
-0.70710678, -0.72424708, -0.74095113, -0.75720885, -0.77301045, -0.78834643, -0.80320753, -0.81758481,
-0.83146961, -0.84485357, -0.85772861, -0.87008699, -0.88192126, -0.89322430, -0.90398929, -0.91420976,
-0.92387953, -0.93299280, -0.94154407, -0.94952818, -0.95694034, -0.96377607, -0.97003125, -0.97570213,
-0.98078528, -0.98527764, -0.98917651, -0.99247953, -0.99518473, -0.99729046, -0.99879546, -0.99969882,
-0.98078528, -0.98527764, -0.98917651, -0.99247953, -0.99518473, -0.99729046, -0.99879546, -0.99969882,*/
};
const float* const cos_table = &sin_table[64];
// full size table:
// sin = sin_table[i ]
// cos = sin_table[i+64]
//#define SIN(i) sin_table[(i)]
//#define COS(i) sin_table[(i)+64]
// for size use only 0-64 indexes
// sin = i > 64 ? sin_table[128-i] : sin_table[ i];
// cos = i > 64 ?-sin_table[ i-64] : sin_table[64-i];
#define SIN(i) ((i) > 64 ? sin_table[128-(i)] : sin_table[ (i)])
#define COS(i) ((i) > 64 ?-sin_table[ (i)-64] : sin_table[64-(i)])
#endif
/***
@ -104,8 +117,10 @@ static void fft256(float array[][2], const uint8_t dir) {
uint16_t j, k;
for (j = i, k = 0; j < i + halfsize; j++, k += tablestep) {
uint16_t l = j + halfsize;
float tpre = array[l][real] * cos_table[k] + array[l][imag] * sin_table[k];
float tpim = -array[l][real] * sin_table[k] + array[l][imag] * cos_table[k];
float s = SIN(k);
float c = COS(k);
float tpre = array[l][real] * c + array[l][imag] * s;
float tpim = -array[l][real] * s + array[l][imag] * c;
array[l][real] = array[j][real] - tpre;
array[l][imag] = array[j][imag] - tpim;
array[j][real] += tpre;