LDCLRB, LDCLRAB, LDCLRALB, LDCLRLB Atomic bit clear on byte in memory This instruction atomically loads an 8-bit byte from memory, performs a bitwise AND with the complement of 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, LDCLRAB and LDCLRALB load from memory with acquire semantics. LDCLRLB and LDCLRALB store to memory with release semantics. LDCLRB 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 STCLRB, STCLRLB A == '0' && Rt == '11111' See below for details of when the alias is preferred. 0 0 1 1 1 0 0 0 1 0 0 0 1 0 0 1 0 LDCLRAB <Ws>, <Wt>, [<Xn|SP>] 1 1 LDCLRALB <Ws>, <Wt>, [<Xn|SP>] 0 0 LDCLRB <Ws>, <Wt>, [<Xn|SP>] 0 1 LDCLRLB <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_BIC, acquire, release, tagchecked, privileged); if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n, 64]; constant bits(8) comparevalue = bits(8) UNKNOWN; // Irrelevant when not executing CAS constant bits(8) value = X[s, 8]; constant bits(8) data = MemAtomic(address, comparevalue, value, accdesc); if t != 31 then X[t, 32] = ZeroExtend(data, 32);