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Sim/COB: avoid UB in float-to-short angle casts (fixes arm64/x86 desync) #3075

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Merged
lostsquirrel1 merged 2 commits into from
Jul 28, 2026
Merged

Sim/COB: avoid UB in float-to-short angle casts (fixes arm64/x86 desync) #3075

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1c2385a
Sim/COB: avoid UB in float-to-short angle casts (fixes arm64/x86 desync)
tomjn Jun 29, 2026
58dbc16
address review: extract RadAngleToCobShort helper with explanatory co…
tomjn Jun 29, 2026
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24 changes: 19 additions & 5 deletions rts/Sim/Units/Scripts/CobInstance.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,20 @@
/******************************************************************************/
/******************************************************************************/

// COB scripts encode angles as TA units where a full turn is COBSCALE (65536),
// so any angle past a half turn exceeds the range of a signed short and is meant
// to wrap around (it is a circular 16-bit angle). Truncating the scaled value to
// int first is well defined for the bounded angles the sim feeds in, and the
// following int->short narrowing performs that modular wrap deterministically.
// Converting straight from float to short would be undefined behaviour once the
// value leaves short's range, and produced different results on arm64 vs x86,
// desyncing multiplayer.
static inline short RadAngleToCobShort(float radAngle)
{
return static_cast<short>(static_cast<int>(radAngle * RAD2TAANG));
}


CR_BIND_DERIVED(CCobInstance, CUnitScript, )

CR_REG_METADATA(CCobInstance, (
Expand Down Expand Up @@ -237,7 +251,7 @@ void CCobInstance::WindChanged(float heading, float speed)
{
ZoneScoped;
Call(COBFN_SetSpeed, int(speed * 3000.0f));
Call(COBFN_SetDirection, short(heading * RAD2TAANG));
Call(COBFN_SetDirection, RadAngleToCobShort(heading));
}


Expand Down Expand Up @@ -387,8 +401,8 @@ void CCobInstance::StartBuilding(float heading, float pitch)
std::array<int, 1 + MAX_COB_ARGS> callinArgs;

callinArgs[0] = 2;
callinArgs[1] = short(heading * RAD2TAANG);
callinArgs[2] = short( pitch * RAD2TAANG);
callinArgs[1] = RadAngleToCobShort(heading);
callinArgs[2] = RadAngleToCobShort(pitch);

Call(COBFN_StartBuilding, callinArgs);
}
Expand Down Expand Up @@ -439,8 +453,8 @@ void CCobInstance::AimWeapon(int weaponNum, float heading, float pitch)
std::array<int, 1 + MAX_COB_ARGS> callinArgs;

callinArgs[0] = 2;
callinArgs[1] = short(heading * RAD2TAANG);
callinArgs[2] = short( pitch * RAD2TAANG);
callinArgs[1] = RadAngleToCobShort(heading);
callinArgs[2] = RadAngleToCobShort(pitch);

Call(COBFN_AimPrimary + COBFN_Weapon_Funcs * weaponNum, callinArgs, CBAimWeapon, weaponNum, nullptr);
}
Expand Down
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