LDUMINB, LDUMINAB, LDUMINALB, LDUMINLB

Atomic unsigned minimum on byte in memory atomically loads an 8-bit byte 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.

For more information about memory ordering semantics see Load-Acquire, Store-Release.

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

Integer
(ARMv8.1)

313029282726252423222120191817161514131211109876543210
00111000AR1Rs011100RnRt
sizeVo3opc

Acquire (A == 1 && R == 0)

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

Acquire and release (A == 1 && R == 1)

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

No memory ordering (A == 0 && R == 0 && Rt != 11111)

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

Release (A == 0 && R == 1 && Rt != 11111)

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

if !HaveAtomicExt() then UnallocatedEncoding(); integer t = UInt(Rt); integer n = UInt(Rn); integer s = UInt(Rs); AccType ldacctype = if A == '1' && Rt != '11111' then AccType_ORDEREDRW else AccType_ATOMICRW; AccType stacctype = if R == '1' then AccType_ORDEREDRW else AccType_ATOMICRW;

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.

Operation

bits(64) address; bits(8) value; bits(8) data; bits(8) result; value = X[s]; if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n]; data = Mem[address, 1, ldacctype]; result = if UInt(data) > UInt(value) then value else data; // All observers in the shareability domain observe the // following load and store atomically. Mem[address, 1, stacctype] = result; X[t] = ZeroExtend(data, 32);


Internal version only: isa v25.07, AdvSIMD v23.0, pseudocode v31.3

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