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LDSMINB, LDSMINAB, LDSMINALB, LDSMINLB

Atomic signed minimum on byte in memory atomically loads an 8-bit byte from memory, compares it against the value held in a register, and stores the smaller value back to memory, treating the values as signed numbers. The value initially loaded from memory is returned in the destination register.

  • If the destination register is not WZR, LDSMINAB and LDSMINALB load from memory with acquire semantics.
  • LDSMINLB and LDSMINALB store to memory with release semantics.
  • LDSMINB 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 STSMINB, STSMINLB.

Integer
(Armv8.1)

313029282726252423222120191817161514131211109876543210
00111000AR1Rs010100RnRt
sizeopc

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

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

LDSMINALB (A == 1 && R == 1)

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

LDSMINB (A == 0 && R == 0)

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

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

LDSMINLB <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
STSMINB, STSMINLBA == '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_SMIN, 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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