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Merge pull request #416 from dekutree64/dev
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Fix for #415 sin/cos integer overflow on 16-bit CPUs
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runger1101001 authored Jul 18, 2024
2 parents eb4fd7f + b203b83 commit c27bc4b
Showing 1 changed file with 6 additions and 5 deletions.
11 changes: 6 additions & 5 deletions src/common/foc_utils.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -9,20 +9,21 @@ __attribute__((weak)) float _sin(float a){
// 16 bit precision on sine value, 8 bit fractional value for interpolation, 6bit LUT size
// resulting precision compared to stdlib sine is 0.00006480 (RMS difference in range -PI,PI for 3217 steps)
static uint16_t sine_array[65] = {0,804,1608,2411,3212,4011,4808,5602,6393,7180,7962,8740,9512,10279,11039,11793,12540,13279,14010,14733,15447,16151,16846,17531,18205,18868,19520,20160,20788,21403,22006,22595,23170,23732,24279,24812,25330,25833,26320,26791,27246,27684,28106,28511,28899,29269,29622,29957,30274,30572,30853,31114,31357,31581,31786,31972,32138,32286,32413,32522,32610,32679,32729,32758,32768};
int32_t t1, t2;
unsigned int i = (unsigned int)(a * (64*4*256.0f/_2PI));
int t1, t2, frac = i & 0xff;
int frac = i & 0xff;
i = (i >> 8) & 0xff;
if (i < 64) {
t1 = sine_array[i]; t2 = sine_array[i+1];
t1 = (int32_t)sine_array[i]; t2 = (int32_t)sine_array[i+1];
}
else if(i < 128) {
t1 = sine_array[128 - i]; t2 = sine_array[127 - i];
t1 = (int32_t)sine_array[128 - i]; t2 = (int32_t)sine_array[127 - i];
}
else if(i < 192) {
t1 = -sine_array[-128 + i]; t2 = -sine_array[-127 + i];
t1 = -(int32_t)sine_array[-128 + i]; t2 = -(int32_t)sine_array[-127 + i];
}
else {
t1 = -sine_array[256 - i]; t2 = -sine_array[255 - i];
t1 = -(int32_t)sine_array[256 - i]; t2 = -(int32_t)sine_array[255 - i];
}
return (1.0f/32768.0f) * (t1 + (((t2 - t1) * frac) >> 8));
}
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