RCWCASP, RCWCASPA, RCWCASPL, RCWCASPAL Read check write compare and swap quadword in memory This instruction reads a 128-bit quadword from memory, and compares it against the value held in a pair of registers. If the comparison is equal, the value in a second pair of registers is conditionally written to memory. Storing back to memory is conditional on RCW Checks. If the write is performed, the read and the write occur atomically such that no other modification of the memory location can take place between the read and the write. This instruction updates the condition flags based on the result of the update of memory. RCWCASPA and RCWCASPAL load from memory with acquire semantics. RCWCASPL and RCWCASPAL store to memory with release semantics. RCWCASP has neither acquire nor release semantics. If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored. 0 0 0 1 1 0 0 1 1 0 0 0 0 1 1 0 0 RCWCASP <Xs>, <X(s+1)>, <Xt>, <X(t+1)>, [<Xn|SP>] 1 0 RCWCASPA <Xs>, <X(s+1)>, <Xt>, <X(t+1)>, [<Xn|SP>] 1 1 RCWCASPAL <Xs>, <X(s+1)>, <Xt>, <X(t+1)>, [<Xn|SP>] 0 1 RCWCASPL <Xs>, <X(s+1)>, <Xt>, <X(t+1)>, [<Xn|SP>] if !IsFeatureImplemented(FEAT_D128) || !IsFeatureImplemented(FEAT_THE) then UNDEFINED; if Rs<0> == '1' then UNDEFINED; if Rt<0> == '1' then UNDEFINED; constant integer s = UInt(Rs); constant integer t = UInt(Rt); constant integer n = UInt(Rn); constant boolean acquire = A == '1'; constant boolean release = R == '1'; constant boolean soft = FALSE; constant boolean tagchecked = n != 31; <Xs> Is the 64-bit name of the first general-purpose register to be compared and loaded, encoded in the "Rs" field. <Xs> must be an even-numbered register. <X(s+1)> Is the 64-bit name of the second general-purpose register to be compared and loaded. <Xt> Is the 64-bit name of the first general-purpose register to be conditionally stored, encoded in the "Rt" field. <Xt> must be an even-numbered register. <X(t+1)> Is the 64-bit name of the second general-purpose register to be conditionally stored. <Xn|SP> Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field. if !IsD128Enabled(PSTATE.EL) then UNDEFINED; bits(64) address; bits(128) newdata; bits(128) compdata; bits(128) readdata; bits(4) nzcv; constant bits(64) s1 = X[s, 64]; constant bits(64) s2 = X[s+1, 64]; constant bits(64) t1 = X[t, 64]; constant bits(64) t2 = X[t+1, 64]; constant AccessDescriptor accdesc = CreateAccDescRCW(MemAtomicOp_CAS, soft, acquire, release, tagchecked); compdata = if BigEndian(accdesc.acctype) then s1:s2 else s2:s1; newdata = if BigEndian(accdesc.acctype) then t1:t2 else t2:t1; if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n, 64]; (nzcv, readdata) = MemAtomicRCW(address, compdata, newdata, accdesc); PSTATE.<N,Z,C,V> = nzcv; if BigEndian(accdesc.acctype) then X[s, 64] = readdata<127:64>; X[s+1, 64] = readdata<63:0>; else X[s, 64] = readdata<63:0>; X[s+1, 64] = readdata<127:64>;