Load register signed halfword (immediate)
This instruction loads a halfword from memory, sign-extends it to 32 bits or 64 bits, and writes the result to a register. The address that is used for the load is calculated from a base register and an immediate offset. For information about addressing modes, see Load/Store addressing modes.
It has encodings from 3 classes: Post-index , Pre-index and Unsigned offset
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| 0 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | x | 0 | imm9 | 0 | 1 | Rn | Rt | ||||||||||||||||
| size | VR | opc | |||||||||||||||||||||||||||||
boolean wback = TRUE; constant boolean postindex = TRUE; constant bits(64) offset = SignExtend(imm9, 64);
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| 0 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | x | 0 | imm9 | 1 | 1 | Rn | Rt | ||||||||||||||||
| size | VR | opc | |||||||||||||||||||||||||||||
boolean wback = TRUE; constant boolean postindex = FALSE; constant bits(64) offset = SignExtend(imm9, 64);
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| 0 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | x | imm12 | Rn | Rt | |||||||||||||||||||
| size | VR | opc | |||||||||||||||||||||||||||||
boolean wback = FALSE; constant boolean postindex = FALSE; constant bits(64) offset = LSL(ZeroExtend(imm12, 64), 1);
For information about the CONSTRAINED UNPREDICTABLE behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors, and particularly LDRSH (immediate).
| <Wt> |
Is the 32-bit name of the general-purpose register to be transferred, 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. |
| <simm> |
Is the signed immediate byte offset, in the range -256 to 255, encoded in the "imm9" field. |
| <Xt> |
Is the 64-bit name of the general-purpose register to be transferred, encoded in the "Rt" field. |
| <pimm> |
Is the optional positive immediate byte offset, a multiple of 2 in the range 0 to 8190, defaulting to 0 and encoded in the "imm12" field as <pimm>/2. |
constant integer t = UInt(Rt); constant integer n = UInt(Rn); constant integer regsize = 64 >> UInt(opc<0>); constant boolean nontemporal = FALSE; constant boolean tagchecked = wback || n != 31; Constraint c; boolean wb_unknown = FALSE; if wback && n == t && n != 31 then c = ConstrainUnpredictable(Unpredictable_WBOVERLAPLD); assert c IN {Constraint_WBSUPPRESS, Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP}; case c of when Constraint_WBSUPPRESS wback = FALSE; // Writeback is suppressed when Constraint_UNKNOWN wb_unknown = TRUE; // Writeback is UNKNOWN when Constraint_UNDEF EndOfDecode(Decode_UNDEF); when Constraint_NOP EndOfDecode(Decode_NOP);
bits(64) address; constant boolean privileged = PSTATE.EL != EL0; constant AccessDescriptor accdesc = CreateAccDescGPR(MemOp_LOAD, nontemporal, privileged, tagchecked); if n == 31 then CheckSPAlignment(); address = SP[64]; else address = X[n, 64]; if !postindex then address = AddressAdd(address, offset, accdesc); constant bits(16) data = Mem[address, 2, accdesc]; X[t, regsize] = SignExtend(data, regsize); if wback then if wb_unknown then address = bits(64) UNKNOWN; elsif postindex then address = AddressAdd(address, offset, accdesc); if n == 31 then SP[64] = address; else X[n, 64] = address;
If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.
Internal version only: aarchmrs v2024-12_rel, pseudocode v2024-12_rel ; Build timestamp: 2024-12-15T22:18
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