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Plane: remove trig calls from constexpr

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Mark Whitehorn 2019-03-25 22:24:33 -06:00 committed by Andrew Tridgell
parent 494a3f86ad
commit b3f093b877
1 changed files with 9 additions and 3 deletions
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12
ArduPlane/tailsitter.cpp
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@ -269,12 +269,18 @@ void QuadPlane::tailsitter_speed_scaling(void)
} else {
// if no airspeed sensor reduce control surface throws at large tilt
// angles (assuming high airspeed)
// ramp down from 1 to max_atten at tilt angles over trans_angle
// (angles here are represented by their cosines)
constexpr float c_trans_angle = cosf(.125f * M_PI);
constexpr float alpha = (1 - max_atten) / (c_trans_angle - cosf(radians(90)));
// Note that the cosf call will be necessary if trans_angle becomes a parameter
// but the C language spec does not guarantee that trig functions can be used
// in constant expressions, even though gcc currently allows it.
constexpr float c_trans_angle = 0.9238795; // cosf(.125f * M_PI)
// alpha = (1 - max_atten) / (c_trans_angle - cosf(radians(90)));
constexpr float alpha = (1 - max_atten) / c_trans_angle;
constexpr float beta = 1 - alpha * c_trans_angle;
const float c_tilt = ahrs_view->get_rotation_body_to_ned().c.z;
if (c_tilt < c_trans_angle) {
spd_scaler = constrain_float(beta + alpha * c_tilt, max_atten, 1.0f);