LDSETH, LDSETAH, LDSETALH, LDSETLH Atomic bit set on halfword in memory This instruction atomically loads a 16-bit halfword from memory, performs a bitwise OR with the value held in a register on it, and stores the result back to memory. The value initially loaded from memory is returned in the destination register. If the destination register is not WZR, LDSETAH and LDSETALH load from memory with acquire semantics. LDSETLH and LDSETALH store to memory with release semantics. LDSETH has neither acquire nor release semantics. For more information about memory ordering semantics, see Load-Acquire, Store-Release. For information about addressing modes, see Load/Store addressing modes. If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored. This instruction is used by the alias STSETH, STSETLH A == '0' && Rt == '11111' See below for details of when the alias is preferred. 0 1 1 1 1 0 0 0 1 0 0 1 1 0 0 1 0 LDSETAH <Ws>, <Wt>, [<Xn|SP>] 1 1 LDSETALH <Ws>, <Wt>, [<Xn|SP>] 0 0 LDSETH <Ws>, <Wt>, [<Xn|SP>] 0 1 LDSETLH <Ws>, <Wt>, [<Xn|SP>] if !IsFeatureImplemented(FEAT_LSE) then UNDEFINED; constant integer s = UInt(Rs); constant integer t = UInt(Rt); constant integer n = UInt(Rn); constant boolean acquire = A == '1' && Rt != '11111'; constant boolean release = R == '1'; constant boolean tagchecked = n != 31; <Ws> Is the 32-bit name of the general-purpose register holding the data value to be operated on with the contents of the memory location, encoded in the "Rs" field. <Wt> Is the 32-bit name of the general-purpose register to be loaded, encoded in the "Rt" field. <Xn|SP> Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field. Alias Conditions bits(64) address; constant boolean privileged = PSTATE.EL != EL0; constant AccessDescriptor accdesc = CreateAccDescAtomicOp(MemAtomicOp_ORR, acquire, release, tagchecked, privileged); if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n, 64]; constant bits(16) comparevalue = bits(16) UNKNOWN; // Irrelevant when not executing CAS constant bits(16) value = X[s, 16]; constant bits(16) data = MemAtomic(address, comparevalue, value, accdesc); if t != 31 then X[t, 32] = ZeroExtend(data, 32);