LDRSB (register) Load register signed byte (register) This instruction calculates an address from a base register value and an offset register value, loads a byte from memory, sign-extends it, and writes it to a register. For information about addressing modes, see Load/Store addressing modes. If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored. 0 0 1 1 1 0 0 0 1 x 1 1 0 1 Z N N LDRSB <Wt>, [<Xn|SP>, (<Wm>|<Xm>), <extend> {<amount>}] 1 0 1 1 LDRSB <Wt>, [<Xn|SP>, <Xm>{, LSL <amount>}] 0 Z N N LDRSB <Xt>, [<Xn|SP>, (<Wm>|<Xm>), <extend> {<amount>}] 0 0 1 1 LDRSB <Xt>, [<Xn|SP>, <Xm>{, LSL <amount>}] if option<1> == '0' then UNDEFINED; // sub-word index constant ExtendType extend_type = DecodeRegExtend(option); constant integer shift = 0; <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. <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 specifier, option <extend> 010 UXTW 110 SXTW 111 SXTX <amount> Is the index shift amount, it must be #0, encoded in "S" as 0 if omitted, or as 1 if present. <Xt> Is the 64-bit name of the general-purpose register to be transferred, encoded in the "Rt" field. constant integer t = UInt(Rt); constant integer n = UInt(Rn); constant integer m = UInt(Rm); constant integer regsize = 64 >> UInt(opc<0>); 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[]; else address = X[n, 64]; address = AddressAdd(address, offset, accdesc); constant bits(8) data = Mem[address, 1, accdesc]; X[t, regsize] = SignExtend(data, regsize);