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@ -211,23 +211,42 @@ inline static fixp_t fixDiv(fixp_interim_t const a, fixp_interim_t const b) |
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* @param angle fixed point radian value |
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* @param angle fixed point radian value |
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* @return Result of the sine function normalized to a range from -FIX to FIX. |
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* @return Result of the sine function normalized to a range from -FIX to FIX. |
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*/ |
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*/ |
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static fixp_t fixSin(fixp_t const fAngle) |
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static fixp_t fixSin(fixp_t fAngle) |
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{ |
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{ |
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// convert given angle to its corresponding lookup table quantization step
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// convert given fixed-point angle to its corresponding quantization step
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ordinary_int_t nNormAng = fAngle / FIX_SIN_DIVIDER; |
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int8_t nSign = 1; |
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// trim that value so that it fits into a range between [0, FIX_SIN_COUNT]
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if (fAngle < 0) |
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nNormAng = (nNormAng - (nNormAng / FIX_SIN_COUNT * FIX_SIN_COUNT) + |
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{ |
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FIX_SIN_COUNT) % FIX_SIN_COUNT; |
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// take advantage of sin(-x) == -sin(x) to avoid neg. operands for "%"
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fAngle = -fAngle; |
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uint8_t nIndex = nNormAng % (FIX_SIN_COUNT / 2); |
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nSign = -1; |
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if (nIndex >= (FIX_SIN_COUNT / 4)) |
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} |
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uint8_t nIndex = (fAngle / FIX_SIN_DIVIDER) % FIX_SIN_COUNT; |
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// now convert that quantization step to an index of our quartered array
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if ((nIndex >= (FIX_SIN_COUNT / 4))) |
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{ |
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if (nIndex < (FIX_SIN_COUNT / 2)) |
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{ |
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{ |
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nIndex = (FIX_SIN_COUNT / 2 - 1) - nIndex; |
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nIndex = (FIX_SIN_COUNT / 2 - 1) - nIndex; |
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} |
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} |
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else |
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{ |
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// an angle > PI means that we have to toggle the sign of the result
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nSign *= -1; |
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if (nIndex < (FIX_SIN_COUNT - (FIX_SIN_COUNT / 4))) |
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{ |
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nIndex = nIndex - (FIX_SIN_COUNT / 2); |
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} |
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else |
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{ |
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nIndex = (FIX_SIN_COUNT - 1) - nIndex; |
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} |
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} |
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} |
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assert(nIndex < (FIX_SIN_COUNT / 4)); |
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assert(nIndex < (FIX_SIN_COUNT / 4)); |
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return ((fixp_t)fix_sine_lut[nIndex]) * |
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return ((fixp_t)fix_sine_lut[nIndex]) * nSign; |
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(nNormAng < (FIX_SIN_COUNT / 2) ? 1 : -1); |
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} |
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} |
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