fork
Dependencies: MPU9250_SPI mbed
Fork of MPU9250_AHRS by
MadgwickAHRS.h@29:6075f35f472f, 2016-07-06 (annotated)
- Committer:
- uribotail
- Date:
- Wed Jul 06 11:44:22 2016 +0000
- Revision:
- 29:6075f35f472f
- Parent:
- 27:7dd32c696d17
20:44wada debag now
Who changed what in which revision?
User | Revision | Line number | New contents of line |
---|---|---|---|
mfurukawa | 17:7a9459ac7469 | 1 | //--------------------------------------------------------------------------------------------------- |
mfurukawa | 17:7a9459ac7469 | 2 | // Definitions |
mfurukawa | 17:7a9459ac7469 | 3 | |
mfurukawa | 17:7a9459ac7469 | 4 | #define sampleFreq 500.0f // sample frequency in Hz |
uribotail | 27:7dd32c696d17 | 5 | #define betaDef 0.0f // 2 * proportional gain |
mfurukawa | 17:7a9459ac7469 | 6 | #define PI 3.14159265358979f |
mfurukawa | 17:7a9459ac7469 | 7 | #define DEGREE2RAD PI/180.0f |
mfurukawa | 17:7a9459ac7469 | 8 | class MadgwickAHRS |
mfurukawa | 17:7a9459ac7469 | 9 | { |
mfurukawa | 17:7a9459ac7469 | 10 | //--------------------------------------------------------------------------------------------------- |
mfurukawa | 17:7a9459ac7469 | 11 | // Variable definitions |
mfurukawa | 17:7a9459ac7469 | 12 | |
mfurukawa | 17:7a9459ac7469 | 13 | private: |
mfurukawa | 17:7a9459ac7469 | 14 | volatile float beta; // 2 * proportional gain (Kp) |
mfurukawa | 17:7a9459ac7469 | 15 | |
mfurukawa | 17:7a9459ac7469 | 16 | //--------------------------------------------------------------------------------------------------- |
mfurukawa | 17:7a9459ac7469 | 17 | // Function declarations |
mfurukawa | 17:7a9459ac7469 | 18 | public: |
mfurukawa | 17:7a9459ac7469 | 19 | volatile float q0,q1,q2,q3; // quaternion of sensor frame relative to auxiliary frame |
mfurukawa | 17:7a9459ac7469 | 20 | |
mfurukawa | 17:7a9459ac7469 | 21 | MadgwickAHRS(); |
mfurukawa | 17:7a9459ac7469 | 22 | void update(float gx, float gy, float gz, float ax, float ay, float az, float mx, float my, float mz); |
mfurukawa | 17:7a9459ac7469 | 23 | void updateIMU(float gx, float gy, float gz, float ax, float ay, float az); |
mfurukawa | 17:7a9459ac7469 | 24 | float invSqrt(float x); |
mfurukawa | 17:7a9459ac7469 | 25 | }; |
mfurukawa | 17:7a9459ac7469 | 26 | //==================================================================================================== |
mfurukawa | 17:7a9459ac7469 | 27 | // Functions |
mfurukawa | 17:7a9459ac7469 | 28 | |
mfurukawa | 17:7a9459ac7469 | 29 | //--------------------------------------------------------------------------------------------------- |
mfurukawa | 17:7a9459ac7469 | 30 | // AHRS algorithm update |
mfurukawa | 17:7a9459ac7469 | 31 | MadgwickAHRS::MadgwickAHRS() |
mfurukawa | 17:7a9459ac7469 | 32 | { |
mfurukawa | 17:7a9459ac7469 | 33 | beta = betaDef; // 2 * proportional gain (Kp) |
mfurukawa | 17:7a9459ac7469 | 34 | q0 = 1.0f; |
mfurukawa | 17:7a9459ac7469 | 35 | q1 = 0.0f; |
mfurukawa | 17:7a9459ac7469 | 36 | q2 = 0.0f; |
mfurukawa | 17:7a9459ac7469 | 37 | q3 = 0.0f; // quaternion of sensor frame relative to auxiliary frame |
mfurukawa | 17:7a9459ac7469 | 38 | } |
mfurukawa | 17:7a9459ac7469 | 39 | void MadgwickAHRS::update(float gx, float gy, float gz, float ax, float ay, float az, float mx, float my, float mz) |
mfurukawa | 17:7a9459ac7469 | 40 | { |
mfurukawa | 17:7a9459ac7469 | 41 | float recipNorm; |
mfurukawa | 17:7a9459ac7469 | 42 | float s0, s1, s2, s3; |
mfurukawa | 17:7a9459ac7469 | 43 | float qDot1, qDot2, qDot3, qDot4; |
mfurukawa | 17:7a9459ac7469 | 44 | float hx, hy; |
mfurukawa | 17:7a9459ac7469 | 45 | float _2q0mx, _2q0my, _2q0mz, _2q1mx, _2bx, _2bz, _4bx, _4bz, _2q0, _2q1, _2q2, _2q3, _2q0q2, _2q2q3, q0q0, q0q1, q0q2, q0q3, q1q1, q1q2, q1q3, q2q2, q2q3, q3q3; |
uribotail | 29:6075f35f472f | 46 | /* |
uribotail | 29:6075f35f472f | 47 | printf("%+4.3f %+4.3f %+4.3f ",gx,gy,gz); |
uribotail | 29:6075f35f472f | 48 | printf("%+4.3f %+4.3f %+4.3f ",ax,ay,az); |
uribotail | 29:6075f35f472f | 49 | printf("%.3f %.3f %.3f ",mx,my,mz); |
uribotail | 29:6075f35f472f | 50 | printf("\n");*/ |
mfurukawa | 17:7a9459ac7469 | 51 | // Use IMU algorithm if magnetometer measurement invalid (avoids NaN in magnetometer normalisation) |
mfurukawa | 17:7a9459ac7469 | 52 | if((mx == 0.0f) && (my == 0.0f) && (mz == 0.0f)) { |
mfurukawa | 17:7a9459ac7469 | 53 | updateIMU(gx, gy, gz, ax, ay, az); |
mfurukawa | 17:7a9459ac7469 | 54 | return; |
mfurukawa | 17:7a9459ac7469 | 55 | } |
mfurukawa | 17:7a9459ac7469 | 56 | |
mfurukawa | 17:7a9459ac7469 | 57 | // Rate of change of quaternion from gyroscope |
mfurukawa | 17:7a9459ac7469 | 58 | qDot1 = 0.5f * (-q1 * gx - q2 * gy - q3 * gz); |
mfurukawa | 17:7a9459ac7469 | 59 | qDot2 = 0.5f * (q0 * gx + q2 * gz - q3 * gy); |
mfurukawa | 17:7a9459ac7469 | 60 | qDot3 = 0.5f * (q0 * gy - q1 * gz + q3 * gx); |
mfurukawa | 17:7a9459ac7469 | 61 | qDot4 = 0.5f * (q0 * gz + q1 * gy - q2 * gx); |
mfurukawa | 17:7a9459ac7469 | 62 | |
mfurukawa | 17:7a9459ac7469 | 63 | // Compute feedback only if accelerometer measurement valid (avoids NaN in accelerometer normalisation) |
mfurukawa | 17:7a9459ac7469 | 64 | if(!((ax == 0.0f) && (ay == 0.0f) && (az == 0.0f))) { |
mfurukawa | 17:7a9459ac7469 | 65 | |
mfurukawa | 17:7a9459ac7469 | 66 | // Normalise accelerometer measurement |
mfurukawa | 17:7a9459ac7469 | 67 | recipNorm = invSqrt(ax * ax + ay * ay + az * az); |
mfurukawa | 17:7a9459ac7469 | 68 | ax *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 69 | ay *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 70 | az *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 71 | |
mfurukawa | 17:7a9459ac7469 | 72 | // Normalise magnetometer measurement |
mfurukawa | 17:7a9459ac7469 | 73 | recipNorm = invSqrt(mx * mx + my * my + mz * mz); |
mfurukawa | 17:7a9459ac7469 | 74 | mx *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 75 | my *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 76 | mz *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 77 | |
mfurukawa | 17:7a9459ac7469 | 78 | // Auxiliary variables to avoid repeated arithmetic |
mfurukawa | 17:7a9459ac7469 | 79 | _2q0mx = 2.0f * q0 * mx; |
mfurukawa | 17:7a9459ac7469 | 80 | _2q0my = 2.0f * q0 * my; |
mfurukawa | 17:7a9459ac7469 | 81 | _2q0mz = 2.0f * q0 * mz; |
mfurukawa | 17:7a9459ac7469 | 82 | _2q1mx = 2.0f * q1 * mx; |
mfurukawa | 17:7a9459ac7469 | 83 | _2q0 = 2.0f * q0; |
mfurukawa | 17:7a9459ac7469 | 84 | _2q1 = 2.0f * q1; |
mfurukawa | 17:7a9459ac7469 | 85 | _2q2 = 2.0f * q2; |
mfurukawa | 17:7a9459ac7469 | 86 | _2q3 = 2.0f * q3; |
mfurukawa | 17:7a9459ac7469 | 87 | _2q0q2 = 2.0f * q0 * q2; |
mfurukawa | 17:7a9459ac7469 | 88 | _2q2q3 = 2.0f * q2 * q3; |
mfurukawa | 17:7a9459ac7469 | 89 | q0q0 = q0 * q0; |
mfurukawa | 17:7a9459ac7469 | 90 | q0q1 = q0 * q1; |
mfurukawa | 17:7a9459ac7469 | 91 | q0q2 = q0 * q2; |
mfurukawa | 17:7a9459ac7469 | 92 | q0q3 = q0 * q3; |
mfurukawa | 17:7a9459ac7469 | 93 | q1q1 = q1 * q1; |
mfurukawa | 17:7a9459ac7469 | 94 | q1q2 = q1 * q2; |
mfurukawa | 17:7a9459ac7469 | 95 | q1q3 = q1 * q3; |
mfurukawa | 17:7a9459ac7469 | 96 | q2q2 = q2 * q2; |
mfurukawa | 17:7a9459ac7469 | 97 | q2q3 = q2 * q3; |
mfurukawa | 17:7a9459ac7469 | 98 | q3q3 = q3 * q3; |
mfurukawa | 17:7a9459ac7469 | 99 | |
mfurukawa | 17:7a9459ac7469 | 100 | // Reference direction of Earth's magnetic field |
mfurukawa | 17:7a9459ac7469 | 101 | hx = mx * q0q0 - _2q0my * q3 + _2q0mz * q2 + mx * q1q1 + _2q1 * my * q2 + _2q1 * mz * q3 - mx * q2q2 - mx * q3q3; |
mfurukawa | 17:7a9459ac7469 | 102 | hy = _2q0mx * q3 + my * q0q0 - _2q0mz * q1 + _2q1mx * q2 - my * q1q1 + my * q2q2 + _2q2 * mz * q3 - my * q3q3; |
mfurukawa | 17:7a9459ac7469 | 103 | _2bx = sqrt(hx * hx + hy * hy); |
mfurukawa | 17:7a9459ac7469 | 104 | _2bz = -_2q0mx * q2 + _2q0my * q1 + mz * q0q0 + _2q1mx * q3 - mz * q1q1 + _2q2 * my * q3 - mz * q2q2 + mz * q3q3; |
mfurukawa | 17:7a9459ac7469 | 105 | _4bx = 2.0f * _2bx; |
mfurukawa | 17:7a9459ac7469 | 106 | _4bz = 2.0f * _2bz; |
mfurukawa | 17:7a9459ac7469 | 107 | |
mfurukawa | 17:7a9459ac7469 | 108 | // Gradient decent algorithm corrective step |
mfurukawa | 17:7a9459ac7469 | 109 | s0 = -_2q2 * (2.0f * q1q3 - _2q0q2 - ax) + _2q1 * (2.0f * q0q1 + _2q2q3 - ay) - _2bz * q2 * (_2bx * (0.5f - q2q2 - q3q3) + _2bz * (q1q3 - q0q2) - mx) + (-_2bx * q3 + _2bz * q1) * (_2bx * (q1q2 - q0q3) + _2bz * (q0q1 + q2q3) - my) + _2bx * q2 * (_2bx * (q0q2 + q1q3) + _2bz * (0.5f - q1q1 - q2q2) - mz); |
mfurukawa | 17:7a9459ac7469 | 110 | s1 = _2q3 * (2.0f * q1q3 - _2q0q2 - ax) + _2q0 * (2.0f * q0q1 + _2q2q3 - ay) - 4.0f * q1 * (1 - 2.0f * q1q1 - 2.0f * q2q2 - az) + _2bz * q3 * (_2bx * (0.5f - q2q2 - q3q3) + _2bz * (q1q3 - q0q2) - mx) + (_2bx * q2 + _2bz * q0) * (_2bx * (q1q2 - q0q3) + _2bz * (q0q1 + q2q3) - my) + (_2bx * q3 - _4bz * q1) * (_2bx * (q0q2 + q1q3) + _2bz * (0.5f - q1q1 - q2q2) - mz); |
mfurukawa | 17:7a9459ac7469 | 111 | s2 = -_2q0 * (2.0f * q1q3 - _2q0q2 - ax) + _2q3 * (2.0f * q0q1 + _2q2q3 - ay) - 4.0f * q2 * (1 - 2.0f * q1q1 - 2.0f * q2q2 - az) + (-_4bx * q2 - _2bz * q0) * (_2bx * (0.5f - q2q2 - q3q3) + _2bz * (q1q3 - q0q2) - mx) + (_2bx * q1 + _2bz * q3) * (_2bx * (q1q2 - q0q3) + _2bz * (q0q1 + q2q3) - my) + (_2bx * q0 - _4bz * q2) * (_2bx * (q0q2 + q1q3) + _2bz * (0.5f - q1q1 - q2q2) - mz); |
mfurukawa | 17:7a9459ac7469 | 112 | s3 = _2q1 * (2.0f * q1q3 - _2q0q2 - ax) + _2q2 * (2.0f * q0q1 + _2q2q3 - ay) + (-_4bx * q3 + _2bz * q1) * (_2bx * (0.5f - q2q2 - q3q3) + _2bz * (q1q3 - q0q2) - mx) + (-_2bx * q0 + _2bz * q2) * (_2bx * (q1q2 - q0q3) + _2bz * (q0q1 + q2q3) - my) + _2bx * q1 * (_2bx * (q0q2 + q1q3) + _2bz * (0.5f - q1q1 - q2q2) - mz); |
mfurukawa | 17:7a9459ac7469 | 113 | recipNorm = invSqrt(s0 * s0 + s1 * s1 + s2 * s2 + s3 * s3); // normalise step magnitude |
mfurukawa | 17:7a9459ac7469 | 114 | s0 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 115 | s1 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 116 | s2 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 117 | s3 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 118 | |
mfurukawa | 17:7a9459ac7469 | 119 | // Apply feedback step |
mfurukawa | 17:7a9459ac7469 | 120 | qDot1 -= beta * s0; |
mfurukawa | 17:7a9459ac7469 | 121 | qDot2 -= beta * s1; |
mfurukawa | 17:7a9459ac7469 | 122 | qDot3 -= beta * s2; |
mfurukawa | 17:7a9459ac7469 | 123 | qDot4 -= beta * s3; |
mfurukawa | 17:7a9459ac7469 | 124 | } |
mfurukawa | 17:7a9459ac7469 | 125 | |
mfurukawa | 17:7a9459ac7469 | 126 | // Integrate rate of change of quaternion to yield quaternion |
mfurukawa | 17:7a9459ac7469 | 127 | q0 += qDot1 * (1.0f / sampleFreq); |
mfurukawa | 17:7a9459ac7469 | 128 | q1 += qDot2 * (1.0f / sampleFreq); |
mfurukawa | 17:7a9459ac7469 | 129 | q2 += qDot3 * (1.0f / sampleFreq); |
mfurukawa | 17:7a9459ac7469 | 130 | q3 += qDot4 * (1.0f / sampleFreq); |
mfurukawa | 17:7a9459ac7469 | 131 | |
mfurukawa | 17:7a9459ac7469 | 132 | // Normalise quaternion |
mfurukawa | 17:7a9459ac7469 | 133 | recipNorm = invSqrt(q0 * q0 + q1 * q1 + q2 * q2 + q3 * q3); |
mfurukawa | 17:7a9459ac7469 | 134 | q0 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 135 | q1 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 136 | q2 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 137 | q3 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 138 | } |
mfurukawa | 17:7a9459ac7469 | 139 | |
mfurukawa | 17:7a9459ac7469 | 140 | //--------------------------------------------------------------------------------------------------- |
mfurukawa | 17:7a9459ac7469 | 141 | // IMU algorithm update |
mfurukawa | 17:7a9459ac7469 | 142 | |
mfurukawa | 17:7a9459ac7469 | 143 | void MadgwickAHRS::updateIMU(float gx, float gy, float gz, float ax, float ay, float az) |
mfurukawa | 17:7a9459ac7469 | 144 | { |
mfurukawa | 17:7a9459ac7469 | 145 | float recipNorm; |
mfurukawa | 17:7a9459ac7469 | 146 | float s0, s1, s2, s3; |
mfurukawa | 17:7a9459ac7469 | 147 | float qDot1, qDot2, qDot3, qDot4; |
mfurukawa | 17:7a9459ac7469 | 148 | float _2q0, _2q1, _2q2, _2q3, _4q0, _4q1, _4q2 ,_8q1, _8q2, q0q0, q1q1, q2q2, q3q3; |
mfurukawa | 17:7a9459ac7469 | 149 | |
mfurukawa | 17:7a9459ac7469 | 150 | // Rate of change of quaternion from gyroscope |
mfurukawa | 17:7a9459ac7469 | 151 | qDot1 = 0.5f * (-q1 * gx - q2 * gy - q3 * gz); |
mfurukawa | 17:7a9459ac7469 | 152 | qDot2 = 0.5f * (q0 * gx + q2 * gz - q3 * gy); |
mfurukawa | 17:7a9459ac7469 | 153 | qDot3 = 0.5f * (q0 * gy - q1 * gz + q3 * gx); |
mfurukawa | 17:7a9459ac7469 | 154 | qDot4 = 0.5f * (q0 * gz + q1 * gy - q2 * gx); |
mfurukawa | 17:7a9459ac7469 | 155 | |
mfurukawa | 17:7a9459ac7469 | 156 | // Compute feedback only if accelerometer measurement valid (avoids NaN in accelerometer normalisation) |
mfurukawa | 17:7a9459ac7469 | 157 | if(!((ax == 0.0f) && (ay == 0.0f) && (az == 0.0f))) { |
mfurukawa | 17:7a9459ac7469 | 158 | |
mfurukawa | 17:7a9459ac7469 | 159 | // Normalise accelerometer measurement |
mfurukawa | 17:7a9459ac7469 | 160 | recipNorm = invSqrt(ax * ax + ay * ay + az * az); |
mfurukawa | 17:7a9459ac7469 | 161 | ax *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 162 | ay *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 163 | az *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 164 | |
mfurukawa | 17:7a9459ac7469 | 165 | // Auxiliary variables to avoid repeated arithmetic |
mfurukawa | 17:7a9459ac7469 | 166 | _2q0 = 2.0f * q0; |
mfurukawa | 17:7a9459ac7469 | 167 | _2q1 = 2.0f * q1; |
mfurukawa | 17:7a9459ac7469 | 168 | _2q2 = 2.0f * q2; |
mfurukawa | 17:7a9459ac7469 | 169 | _2q3 = 2.0f * q3; |
mfurukawa | 17:7a9459ac7469 | 170 | _4q0 = 4.0f * q0; |
mfurukawa | 17:7a9459ac7469 | 171 | _4q1 = 4.0f * q1; |
mfurukawa | 17:7a9459ac7469 | 172 | _4q2 = 4.0f * q2; |
mfurukawa | 17:7a9459ac7469 | 173 | _8q1 = 8.0f * q1; |
mfurukawa | 17:7a9459ac7469 | 174 | _8q2 = 8.0f * q2; |
mfurukawa | 17:7a9459ac7469 | 175 | q0q0 = q0 * q0; |
mfurukawa | 17:7a9459ac7469 | 176 | q1q1 = q1 * q1; |
mfurukawa | 17:7a9459ac7469 | 177 | q2q2 = q2 * q2; |
mfurukawa | 17:7a9459ac7469 | 178 | q3q3 = q3 * q3; |
mfurukawa | 17:7a9459ac7469 | 179 | |
mfurukawa | 17:7a9459ac7469 | 180 | // Gradient decent algorithm corrective step |
mfurukawa | 17:7a9459ac7469 | 181 | s0 = _4q0 * q2q2 + _2q2 * ax + _4q0 * q1q1 - _2q1 * ay; |
mfurukawa | 17:7a9459ac7469 | 182 | s1 = _4q1 * q3q3 - _2q3 * ax + 4.0f * q0q0 * q1 - _2q0 * ay - _4q1 + _8q1 * q1q1 + _8q1 * q2q2 + _4q1 * az; |
mfurukawa | 17:7a9459ac7469 | 183 | s2 = 4.0f * q0q0 * q2 + _2q0 * ax + _4q2 * q3q3 - _2q3 * ay - _4q2 + _8q2 * q1q1 + _8q2 * q2q2 + _4q2 * az; |
mfurukawa | 17:7a9459ac7469 | 184 | s3 = 4.0f * q1q1 * q3 - _2q1 * ax + 4.0f * q2q2 * q3 - _2q2 * ay; |
mfurukawa | 17:7a9459ac7469 | 185 | recipNorm = invSqrt(s0 * s0 + s1 * s1 + s2 * s2 + s3 * s3); // normalise step magnitude |
mfurukawa | 17:7a9459ac7469 | 186 | s0 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 187 | s1 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 188 | s2 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 189 | s3 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 190 | |
mfurukawa | 17:7a9459ac7469 | 191 | // Apply feedback step |
mfurukawa | 17:7a9459ac7469 | 192 | qDot1 -= beta * s0; |
mfurukawa | 17:7a9459ac7469 | 193 | qDot2 -= beta * s1; |
mfurukawa | 17:7a9459ac7469 | 194 | qDot3 -= beta * s2; |
mfurukawa | 17:7a9459ac7469 | 195 | qDot4 -= beta * s3; |
mfurukawa | 17:7a9459ac7469 | 196 | } |
mfurukawa | 17:7a9459ac7469 | 197 | |
mfurukawa | 17:7a9459ac7469 | 198 | // Integrate rate of change of quaternion to yield quaternion |
mfurukawa | 17:7a9459ac7469 | 199 | q0 += qDot1 * (1.0f / sampleFreq); |
mfurukawa | 17:7a9459ac7469 | 200 | q1 += qDot2 * (1.0f / sampleFreq); |
mfurukawa | 17:7a9459ac7469 | 201 | q2 += qDot3 * (1.0f / sampleFreq); |
mfurukawa | 17:7a9459ac7469 | 202 | q3 += qDot4 * (1.0f / sampleFreq); |
mfurukawa | 17:7a9459ac7469 | 203 | |
mfurukawa | 17:7a9459ac7469 | 204 | // Normalise quaternion |
mfurukawa | 17:7a9459ac7469 | 205 | recipNorm = invSqrt(q0 * q0 + q1 * q1 + q2 * q2 + q3 * q3); |
mfurukawa | 17:7a9459ac7469 | 206 | q0 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 207 | q1 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 208 | q2 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 209 | q3 *= recipNorm; |
mfurukawa | 17:7a9459ac7469 | 210 | } |
mfurukawa | 17:7a9459ac7469 | 211 | |
mfurukawa | 17:7a9459ac7469 | 212 | //--------------------------------------------------------------------------------------------------- |
mfurukawa | 17:7a9459ac7469 | 213 | // Fast inverse square-root |
mfurukawa | 17:7a9459ac7469 | 214 | // See: http://en.wikipedia.org/wiki/Fast_inverse_square_root |
mfurukawa | 17:7a9459ac7469 | 215 | |
mfurukawa | 17:7a9459ac7469 | 216 | float MadgwickAHRS::invSqrt(float x) |
mfurukawa | 17:7a9459ac7469 | 217 | { |
mfurukawa | 17:7a9459ac7469 | 218 | float halfx = 0.5f * x; |
mfurukawa | 17:7a9459ac7469 | 219 | float y = x; |
mfurukawa | 17:7a9459ac7469 | 220 | long i = *(long*)&y; |
mfurukawa | 17:7a9459ac7469 | 221 | i = 0x5f3759df - (i>>1); |
mfurukawa | 17:7a9459ac7469 | 222 | y = *(float*)&i; |
mfurukawa | 17:7a9459ac7469 | 223 | y = y * (1.5f - (halfx * y * y)); |
mfurukawa | 17:7a9459ac7469 | 224 | return y; |
mfurukawa | 17:7a9459ac7469 | 225 | } |