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AP_NavEKF2: use union to alias array and struct access to states

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This avoids creating two pointers of different types to the same memory.

Having two pointers to the same memory can lead to the compiler
optimising code such that a write to one pointer is rearranged to be
either before or after a read from the other pointer depending on which
is deemed faster - not a good outcome.
This commit is contained in:
Peter Barker 2018-10-01 09:42:28 +10:00 committed by Peter Barker
parent fb3b976aa2
commit 3a79ae4eca
2 changed files with 6 additions and 4 deletions
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2
libraries/AP_NavEKF2/AP_NavEKF2_core.cpp
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@ -21,8 +21,6 @@ extern const AP_HAL::HAL& hal;
// constructor
NavEKF2_core::NavEKF2_core(void) :
stateStruct(*reinterpret_cast<struct state_elements *>(&statesArray)),
_perf_UpdateFilter(hal.util->perf_alloc(AP_HAL::Util::PC_ELAPSED, "EK2_UpdateFilter")),
_perf_CovariancePrediction(hal.util->perf_alloc(AP_HAL::Util::PC_ELAPSED, "EK2_CovariancePrediction")),
_perf_FuseVelPosNED(hal.util->perf_alloc(AP_HAL::Util::PC_ELAPSED, "EK2_FuseVelPosNED")),

8
libraries/AP_NavEKF2/AP_NavEKF2_core.h
View File

@ -383,7 +383,6 @@ private:
// the states are available in two forms, either as a Vector31, or
// broken down as individual elements. Both are equivalent (same
// memory)
Vector28 statesArray;
struct state_elements {
Vector3f angErr; // 0..2
Vector3f velocity; // 3..5
@ -395,7 +394,12 @@ private:
Vector3f body_magfield; // 19..21
Vector2f wind_vel; // 22..23
Quaternion quat; // 24..27
} &stateStruct;
};
union {
Vector28 statesArray;
struct state_elements stateStruct;
};
struct output_elements {
Quaternion quat; // 0..3