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ARM Compiler armasm User Guide : LDRSB (immediate)

LDRSB (immediate)

Load Register Signed Byte (immediate).

Syntax

LDRSB Wt, [Xn|SP], #simm ; 32-bit general registers, Post-index

LDRSB Xt, [Xn|SP], #simm ; 64-bit general registers, Post-index

LDRSB Wt, [Xn|SP, #simm]! ; 32-bit general registers, Pre-index

LDRSB Xt, [Xn|SP, #simm]! ; 64-bit general registers, Pre-index

LDRSB Wt, [Xn|SP{, #pimm}] ; 32-bit general registers

LDRSB Xt, [Xn|SP{, #pimm}] ; 64-bit general registers

Where:

Wt

Is the 32-bit name of the general-purpose register to be transferred.

simm

Is the signed immediate byte offset, in the range -256 to 255.

Xt

Is the 64-bit name of the general-purpose register to be transferred.

pimm

Is the optional positive immediate byte offset, in the range 0 to 4095, defaulting to 0.

Xn|SP

Is the 64-bit name of the general-purpose base register or stack pointer.

Usage

Load Register Signed Byte (immediate) calculates an address from a base register value and an immediate byte offset, loads a byte from memory, sign-extends it to either 32 or 64 bits, and writes it to a register. For information about memory accesses, see Load/Store addressing modes in the ARMv8-A Architecture Reference Manual.

Note

For information about the CONSTRAINED UNPREDICTABLE behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors in the ARMv8-A Architecture Reference Manual, and particularly LDRSB (immediate) in the ARMv8-A Architecture Reference Manual.
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