LDRSH (register)

Load Register Signed Halfword (register) calculates an address from a base register value and an offset register value, loads a halfword from memory, sign-extends it, and writes it to a register. For information about memory accesses see Load/Store addressing modes.

313029282726252423222120191817161514131211109876543210
011110001x1RmoptionS10RnRt
sizeopc

32-bit (opc == 11)

LDRSH <Wt>, [<Xn|SP>, (<Wm>|<Xm>){, <extend> {<amount>}}]

64-bit (opc == 10)

LDRSH <Xt>, [<Xn|SP>, (<Wm>|<Xm>){, <extend> {<amount>}}]

if option<1> == '0' then UNDEFINED; // sub-word index ExtendType extend_type = DecodeRegExtend(option); integer shift = if S == '1' then 1 else 0;

Assembler Symbols

<Wt>

Is the 32-bit name of the general-purpose register to be transferred, encoded in the "Rt" field.

<Xt>

Is the 64-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.

<Wm>

When option<0> is set to 0, is the 32-bit name of the general-purpose index register, encoded in the "Rm" field.

<Xm>

When option<0> is set to 1, is the 64-bit name of the general-purpose index register, encoded in the "Rm" field.

<extend> Is the index extend/shift specifier, defaulting to LSL, and which must be omitted for the LSL option when <amount> is omitted. encoded in option:
option <extend>
010 UXTW
011 LSL
110 SXTW
111 SXTX
<amount> Is the index shift amount, optional only when <extend> is not LSL. Where it is permitted to be optional, it defaults to #0. It is encoded in S:
S <amount>
0 #0
1 #1

Shared Decode

integer n = UInt(Rn); integer t = UInt(Rt); integer m = UInt(Rm); MemOp memop; boolean signed; integer regsize; if opc<1> == '0' then // store or zero-extending load memop = if opc<0> == '1' then MemOp_LOAD else MemOp_STORE; regsize = 32; signed = FALSE; else // sign-extending load memop = MemOp_LOAD; regsize = if opc<0> == '1' then 32 else 64; signed = TRUE; boolean tag_checked = memop != MemOp_PREFETCH;

Operation

bits(64) offset = ExtendReg(m, extend_type, shift); if HaveMTEExt() then SetNotTagCheckedInstruction(!tag_checked); bits(64) address; bits(16) data; if n == 31 then if memop != MemOp_PREFETCH then CheckSPAlignment(); address = SP[]; else address = X[n]; address = address + offset; case memop of when MemOp_STORE data = X[t]; Mem[address, 2, AccType_NORMAL] = data; when MemOp_LOAD data = Mem[address, 2, AccType_NORMAL]; if signed then X[t] = SignExtend(data, regsize); else X[t] = ZeroExtend(data, regsize); when MemOp_PREFETCH Prefetch(address, t<4:0>);

Operational information

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: isa v30.44, AdvSIMD v27.08, pseudocode v8.5-2019-06_rc2-5-g22901f2, sve v2019-06_rc4 ; Build timestamp: 2019-06-26T22:30

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