ARMV8 short notes

• offset addressing
• pre-index addressing

define like:

load the compass content of the operand 2 to operand 1, then update the operand 2.

ldr r1, [r2, #2]!       r1 = *(r2 + 2); r2 += 2

• post-index addressing

define like:

use the content of operand 2 to update operand 1, then change the content of operand 2 by using operand 3.

ldr r1, [r2], #2            r1 = *r2; r2 += 2

  Compare to pre-index addressing, it does not need "!" to force the updating process.

• pc-relative addressing

The target label must be located within ±4 kilobytes of the ldr instruction.

ldr r1, lable_offset

where the label_offset will be calculated by the assembler.

 

For both the second and the third one can accelerate the process for handling array elements, since the array data structures be like in C.