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LDUMIN, LDUMINA, LDUMINAL, LDUMINL

Atomic unsigned minimum on word or doubleword in memory atomically loads a 32-bit word or 64-bit doubleword from memory, compares it against the value held in a register, and stores the smaller value back to memory, treating the values as unsigned numbers. The value initially loaded from memory is returned in the destination register.

  • If the destination register is not one of WZR or XZR, LDUMINA and LDUMINAL load from memory with acquire semantics.
  • LDUMINL and LDUMINAL store to memory with release semantics.
  • LDUMIN 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 STUMIN, STUMINL.

Integer
(Armv8.1)

313029282726252423222120191817161514131211109876543210
1x111000AR1Rs011100RnRt
sizeopc

32-bit LDUMIN (size == 10 && A == 0 && R == 0)

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

32-bit LDUMINA (size == 10 && A == 1 && R == 0)

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

32-bit LDUMINAL (size == 10 && A == 1 && R == 1)

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

32-bit LDUMINL (size == 10 && A == 0 && R == 1)

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

64-bit LDUMIN (size == 11 && A == 0 && R == 0)

LDUMIN <Xs>, <Xt>, [<Xn|SP>]

64-bit LDUMINA (size == 11 && A == 1 && R == 0)

LDUMINA <Xs>, <Xt>, [<Xn|SP>]

64-bit LDUMINAL (size == 11 && A == 1 && R == 1)

LDUMINAL <Xs>, <Xt>, [<Xn|SP>]

64-bit LDUMINL (size == 11 && A == 0 && R == 1)

LDUMINL <Xs>, <Xt>, [<Xn|SP>]

if !HaveAtomicExt() then UNDEFINED;
integer t = UInt(Rt);
integer n = UInt(Rn);
integer s = UInt(Rs);

integer datasize = 8 << UInt(size);
integer regsize = if datasize == 64 then 64 else 32;
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.

<Xs>

Is the 64-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.

<Xt>

Is the 64-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
STUMIN, STUMINLA == '0' && Rt == '11111'

Operation

bits(64) address;
bits(datasize) value;
bits(datasize) data;
bits(datasize) result;

if HaveMTEExt() then
    SetNotTagCheckedInstruction(!tag_checked);

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

// All observers in the shareability domain observe the
// following load and store atomically.
data = Mem[address, datasize DIV 8, ldacctype];

result = if UInt(data) > UInt(value) then value else data;

Mem[address, datasize DIV 8, stacctype] = result;

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

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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