LDRSW (register)

Load register signed word (register)

This instruction calculates an address from a base register value and an offset register value, loads a word from memory, sign-extends it to form a 64-bit value, and writes it to a register. The offset register value can be shifted left by 0 or 2 bits. For information about addressing modes, see Load/Store addressing modes.

Encoding: 64-bit

313029282726252423222120191817161514131211109876543210
1011100010110
sizeVRopcRmoptionSRnRt

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

Decoding algorithm

if option<1> == '0' then EndOfDecode(Decode_UNDEF);             // sub-word index
constant ExtendType extend_type = DecodeRegExtend(option);
constant integer shift = if S == '1' then 2 else 0;

Operation

constant integer t = UInt(Rt);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant boolean nontemporal = FALSE;
constant boolean tagchecked = TRUE;
constant bits(64) offset = ExtendReg(m, extend_type, shift, 64);
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];

address = AddressAdd(address, offset, accdesc);

constant bits(32) data = Mem[address, 4, accdesc];
X[t, 64] = SignExtend(data, 64);

Explanations

<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>: <amount>:

Operational Notes

If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.