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STUMAX, STUMAXL

Atomic unsigned maximum on word or doubleword in memory, without return, atomically loads a 32-bit word or 64-bit doubleword from memory, compares it against the value held in a register, and stores the larger value back to memory, treating the values as unsigned numbers.

  • STUMAX has no memory ordering semantics.
  • STUMAXL stores to memory with release semantics, as described in Load-Acquire, Store-Release.

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

This is an alias of LDUMAX, LDUMAXA, LDUMAXAL, LDUMAXL. This means:

Integer
(Armv8.1)

313029282726252423222120191817161514131211109876543210
1x1110000R1Rs011000Rn11111
sizeAopcRt

32-bit LDUMAX alias (size == 10 && R == 0)

STUMAX <Ws>, [<Xn|SP>]

is equivalent to

LDUMAX <Ws>, WZR, [<Xn|SP>]

and is always the preferred disassembly.

32-bit LDUMAXL alias (size == 10 && R == 1)

STUMAXL <Ws>, [<Xn|SP>]

is equivalent to

LDUMAXL <Ws>, WZR, [<Xn|SP>]

and is always the preferred disassembly.

64-bit LDUMAX alias (size == 11 && R == 0)

STUMAX <Xs>, [<Xn|SP>]

is equivalent to

LDUMAX <Xs>, XZR, [<Xn|SP>]

and is always the preferred disassembly.

64-bit LDUMAXL alias (size == 11 && R == 1)

STUMAXL <Xs>, [<Xn|SP>]

is equivalent to

LDUMAXL <Xs>, XZR, [<Xn|SP>]

and is always the preferred disassembly.

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.

<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.

<Xn|SP>

Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.

Operation

The description of LDUMAX, LDUMAXA, LDUMAXAL, LDUMAXL gives the operational pseudocode for this instruction.

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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