You copied the Doc URL to your clipboard.


Atomic unsigned maximum on byte in memory, without return.


STUMAXB Ws, [Xn|SP] ; No memory ordering general registers

STUMAXLB Ws, [Xn|SP] ; Release general registers


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.
Is the 64-bit name of the general-purpose base register or stack pointer.

Architectures supported

Supported in the Arm®v8.1 architecture and later.


Atomic unsigned maximum on byte in memory, without return, 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 has no memory ordering semantics.
  • STUMAXLB stores to memory with release semantics, as described in Load-Acquire, Store-Release.

For information about memory accesses see Load/Store addressing modes in the Arm® Architecture Reference Manual Arm®v8, for Arm®v8‑A architecture profile.