SETPT, SETMT, SETET

Memory Set, unprivileged. These instructions perform a memory set using the value in the bottom byte of the source register. The prologue, main, and epilogue instructions are expected to be run in succession and to appear consecutively in memory: SETPT, then SETMT, and then SETET.

SETPT performs some preconditioning of the arguments suitable for using the SETMT instruction, and performs an implementation defined amount of the memory set. SETMT performs an implementation defined amount of the memory set. SETET performs the last part of the memory set.


Note

The inclusion of implementation defined amounts of memory set allows some optimization of the size that can be performed.


The architecture supports two algorithms for the memory set: option A and option B. Which algorithm is used is implementation defined.


Note

Portable software should not assume that the choice of algorithm is constant.


After execution of SETPT, option A (which results in encoding PSTATE.C = 0):

After execution of SETPT, option B (which results in encoding PSTATE.C = 1):

For SETMT, option A (encoded by PSTATE.C = 0), the format of the arguments is:

For SETMT, option B (encoded by PSTATE.C = 1), the format of the arguments is:

For SETET, option A (encoded by PSTATE.C = 0), the format of the arguments is:

For SETET, option B (encoded by PSTATE.C = 1), the format of the arguments is:

Integer
(FEAT_MOPS)

313029282726252423222120191817161514131211109876543210
sz011001110Rsxx0101RnRd
op2

Epilogue (op2 == 1001)

SETET [<Xd>]!, <Xn>!, <Xs>

Main (op2 == 0101)

SETMT [<Xd>]!, <Xn>!, <Xs>

Prologue (op2 == 0001)

SETPT [<Xd>]!, <Xn>!, <Xs>

if !HaveFeatMOPS() || sz != '00' then UNDEFINED; integer d = UInt(Rd); integer s = UInt(Rs); integer n = UInt(Rn); bits(2) options = op2<1:0>; boolean nontemporal = options<1> == '1'; MOPSStage stage; case op2<3:2> of when '00' stage = MOPSStage_Prologue; when '01' stage = MOPSStage_Main; when '10' stage = MOPSStage_Epilogue; otherwise UNDEFINED; CheckMOPSEnabled(); if s == n || s == d || n == d || d == 31 || n == 31 then Constraint c = ConstrainUnpredictable(Unpredictable_MOPSOVERLAP31); assert c IN {Constraint_UNDEF, Constraint_NOP}; case c of when Constraint_UNDEF UNDEFINED; when Constraint_NOP EndOfInstruction();

For information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors, and particularly Memory Copy and Memory Set SET*.

Assembler Symbols

<Xd>

For the epilogue and main variant: is the 64-bit name of the general-purpose register that holds an encoding of the destination address and for option B is updated by the instruction, encoded in the "Rd" field.

For the prologue variant: is the 64-bit name of the general-purpose register that holds the destination address and is updated by the instruction, encoded in the "Rd" field.

<Xn>

For the epilogue variant: is the 64-bit name of the general-purpose register that holds the number of bytes to be set and is set to zero at the end of the instruction, encoded in the "Rn" field.

For the main variant: is the 64-bit name of the general-purpose register that holds an encoding of the number of bytes to be set and is updated by the instruction, encoded in the "Rn" field.

For the prologue variant: is the 64-bit name of the general-purpose register that holds the number of bytes to be set and is updated by the instruction, encoded in the "Rn" field.

<Xs>

Is the 64-bit name of the general-purpose register that holds the source data, encoded in the "Rs" field.

Operation

bits(64) toaddress = X[d, 64]; bits(64) setsize = X[n, 64]; bits(8) data = X[s, 8]; bits(4) nzcv = PSTATE.<N,Z,C,V>; boolean is_setg = FALSE; integer B; boolean implements_option_a = SETOptionA(); boolean privileged = if options<0> == '1' then AArch64.IsUnprivAccessPriv() else PSTATE.EL != EL0; AccessDescriptor accdesc = CreateAccDescMOPS(MemOp_STORE, privileged, nontemporal); if stage == MOPSStage_Prologue then if setsize<63> == '1' then setsize = 0x7FFFFFFFFFFFFFFF<63:0>; if implements_option_a then nzcv = '0000'; toaddress = toaddress + setsize; setsize = Zeros(64) - setsize; else nzcv = '0010'; else CheckMemSetParams(stage, implements_option_a, nzcv, options, d, s, n, toaddress, setsize, is_setg); bits(64) stagesetsize = MemSetStageSize(stage, toaddress, setsize, is_setg); if implements_option_a then while SInt(stagesetsize) < 0 do // IMP DEF selection of the block size that is worked on. While many // implementations might make this constant, that is not assumed. B = SETSizeChoice(toaddress, setsize, 1); assert B <= -1 * SInt(stagesetsize); Mem[toaddress+setsize, B, accdesc] = Replicate(data, B); setsize = setsize + B; stagesetsize = stagesetsize + B; if stage != MOPSStage_Prologue then X[n, 64] = setsize; else while UInt(stagesetsize) > 0 do // IMP DEF selection of the block size that is worked on. While many // implementations might make this constant, that is not assumed. B = SETSizeChoice(toaddress, setsize, 1); assert B <= UInt(stagesetsize); Mem[toaddress, B, accdesc] = Replicate(data, B); toaddress = toaddress + B; setsize = setsize - B; stagesetsize = stagesetsize - B; if stage != MOPSStage_Prologue then X[n, 64] = setsize; X[d, 64] = toaddress; if stage == MOPSStage_Prologue then X[n, 64] = setsize; X[d, 64] = toaddress; PSTATE.<N,Z,C,V> = nzcv;


Internal version only: isa v33.64, AdvSIMD v29.12, pseudocode v2023-06_rel, sve v2023-06_rel ; Build timestamp: 2023-07-04T19:42

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