integer n = UInt(Rn); integer t = UInt(Rt); boolean tagchecked = wback || n != 31; boolean rt_unknown = FALSE; Constraint c; if wback && n == t && n != 31 then c = ConstrainUnpredictable(Unpredictable_WBOVERLAPST); assert c IN {Constraint_NONE, Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP}; case c of when Constraint_NONE rt_unknown = FALSE; // value stored is original value when Constraint_UNKNOWN rt_unknown = TRUE; // value stored is UNKNOWN when Constraint_UNDEF UNDEFINED; when Constraint_NOP EndOfInstruction();

bits(64) address; bits(16) data; boolean privileged = PSTATE.EL != EL0; AccessDescriptor accdesc = CreateAccDescGPR(MemOp_STORE, FALSE, privileged, tagchecked); if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n, 64]; if !postindex then address = GenerateAddress(address, offset, accdesc); if rt_unknown then data = bits(16) UNKNOWN; else data = X[t, 16]; Mem[address, 2, accdesc] = data; if wback then if postindex then address = GenerateAddress(address, offset, accdesc); if n == 31 then SP[] = address; else X[n, 64] = address;