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Fix fixed-point conversion precision to avoid overflow #110

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Merged
merged 1 commit into from
Oct 17, 2025
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Fix fixed-point conversion precision to avoid overflow #110

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10 changes: 9 additions & 1 deletion src/trig.c
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Original file line number Diff line number Diff line change
Expand Up @@ -148,7 +148,15 @@ static twin_angle_t twin_atan2_first_quadrant(twin_fixed_t y, twin_fixed_t x)
}
}

return (twin_angle_t) (double) angle / (32768.0) * TWIN_ANGLE_360;
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Does this commit also aim to fix the incorrect casting of the variable angle from twin_angle_t to double?

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Does this commit also aim to fix the incorrect casting of the variable angle from twin_angle_t to double?

Yes, intentionally.

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Then, why didn't you write this purpose on this commit log ?

/* Fixed-point conversion: angle / 32768 * TWIN_ANGLE_360
* Simplified: angle * 2^12 / 2^15 = angle / 8
* Use integer division (not right shift) to match original
* truncate-towards-zero behavior for negative values. Right shift would
* round towards negative infinity, causing precision errors for
* non-multiples of 8. Avoids overflow since no intermediate multiplication
* required.
*/
return (twin_angle_t) (angle / 8);
}

twin_angle_t twin_atan2(twin_fixed_t y, twin_fixed_t x)
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