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a/math: Refactor m_clock_offset_a2b

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Avoid limited precision float operations on large 64-bit
integers. The clock averaging was basically not working
once the clock values got large
This commit is contained in:
Jan Schmidt 2024-01-02 15:19:35 +11:00 committed by Jakob Bornecrantz
parent a1f385eb0d
commit 3d534bcc1d
1 changed files with 8 additions and 2 deletions
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10
src/xrt/auxiliary/math/m_clock_offset.h
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@ -33,13 +33,19 @@ extern "C" {
static inline timepoint_ns
m_clock_offset_a2b(float freq, timepoint_ns a, timepoint_ns b, time_duration_ns *inout_a2b)
{
// This formulation of exponential filtering uses a fixed-precision integer for the
// alpha value and operates on the delta between the old and new a2b to avoid
// precision / overflow problems.
// Totally arbitrary way of computing alpha, if you have a better one, replace it
const float alpha = 1.0 - 12.5 / freq; // Weight to put on accumulated a2b
const time_duration_ns alpha = 1000 * (1.0 - 12.5 / freq); // Weight to put on accumulated a2b
time_duration_ns old_a2b = *inout_a2b;
time_duration_ns got_a2b = b - a;
time_duration_ns new_a2b = old_a2b * alpha + got_a2b * (1.0 - alpha);
time_duration_ns new_a2b;
if (old_a2b == 0) { // a2b has not been set yet
new_a2b = got_a2b;
} else {
new_a2b = ((old_a2b - got_a2b) * alpha) / 1000 + got_a2b;
}
*inout_a2b = new_a2b;
return a + new_a2b;