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LDADDB, LDADDAB, LDADDALB, LDADDLB

Atomic add on byte in memory atomically loads an 8-bit byte from memory, adds the value held in a register to 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, LDADDAB and LDADDALB load from memory with acquire semantics.
  • LDADDLB and LDADDALB store to memory with release semantics.
  • LDADDB has no memory ordering requirements.

For more information about memory ordering semantics see Load-Acquire, Store-Release.

For information about memory accesses see Load/Store addressing modes.

This instruction is used by the alias STADDB, STADDLB.

Integer
(Armv8.1)

313029282726252423222120191817161514131211109876543210
00111000AR1Rs000000RnRt
sizeopc

LDADDAB (A == 1 && R == 0)

LDADDAB <Ws>, <Wt>, [<Xn|SP>]

LDADDALB (A == 1 && R == 1)

LDADDALB <Ws>, <Wt>, [<Xn|SP>]

LDADDB (A == 0 && R == 0)

LDADDB <Ws>, <Wt>, [<Xn|SP>]

LDADDLB (A == 0 && R == 1)

LDADDLB <Ws>, <Wt>, [<Xn|SP>]

if !HaveAtomicExt() then UNDEFINED;

integer t = UInt(Rt);
integer n = UInt(Rn);
integer s = UInt(Rs);

AccType ldacctype = if A == '1' && Rt != '11111' then AccType_ORDEREDATOMICRW else AccType_ATOMICRW;
AccType stacctype = if R == '1' then AccType_ORDEREDATOMICRW else AccType_ATOMICRW;
boolean tag_checked = n != 31;

Assembler Symbols

<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

AliasIs preferred when
STADDB, STADDLBA == '0' && Rt == '11111'

Operation

bits(64) address;
bits(8) value;
bits(8) data;

if HaveMTEExt() then
    SetNotTagCheckedInstruction(!tag_checked);

value = X[s];
if n == 31 then
    CheckSPAlignment();
    address = SP[];
else
    address = X[n];

data = MemAtomic(address, MemAtomicOp_ADD, value, ldacctype, stacctype);

if t != 31 then
    X[t] = ZeroExtend(data, 32);

Operational information

If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.

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