LDUMAXH, LDUMAXAH, LDUMAXALH, LDUMAXLH
Atomic unsigned maximum on halfword in memory atomically loads a 16-bit halfword 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. The value initially loaded from memory is returned in the destination register.
- If the destination register is not WZR, LDUMAXAH and LDUMAXALH load from memory with acquire semantics.
- LDUMAXLH and LDUMAXALH store to memory with release semantics.
- LDUMAXH has neither acquire nor release semantics.
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 STUMAXH, STUMAXLH.
Integer
(Armv8.1)
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 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | A | R | 1 | Rs | 0 | 1 | 1 | 0 | 0 | 0 | Rn | Rt | ||||||||||||
size | opc |
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
Alias | Is preferred when |
---|---|
STUMAXH, STUMAXLH | A == '0' && Rt == '11111' |
Operation
bits(64) address; bits(16) value; bits(16) data; if HaveMTEExt() then SetTagCheckedInstruction(tag_checked); value = X[s]; if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n]; data = MemAtomic(address, MemAtomicOp_UMAX, 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.