STUMAXB, STUMAXLB

Atomic unsigned maximum on byte in memory, without return

This instruction atomically loads an 8-bit byte 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.

STUMAXB does not have release semantics.
STUMAXLB stores to memory with release semantics, as described in Load-Acquire, Store-Release.

For information about addressing modes, see Load/Store addressing modes.

This is an alias of LDUMAXB, LDUMAXAB, LDUMAXALB, LDUMAXLB. This means:

The encodings in this description are named to match the encodings of LDUMAXB, LDUMAXAB, LDUMAXALB, LDUMAXLB.
The description of LDUMAXB, LDUMAXAB, LDUMAXALB, LDUMAXLB gives the operational pseudocode, any constrained unpredictable behavior, and any operational information for this instruction.

Integer

(FEAT_LSE)

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	0	1	1	1	0	0	0	0	R	1	Rs					0	1	1	0	0	0	Rn					1	1	1	1	1
size					VR			A								o3	opc										Rt

Encoding for the No memory ordering variant

Applies when (R == 0)

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

is equivalent to

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

and is always the preferred disassembly.

Encoding for the Release variant

Applies when (R == 1)

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

is equivalent to

LDUMAXLB <Ws>, WZR, [<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.

<Xn|SP>

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

Operation