Page 92 - ARM 64 Bit Assembly Language

Load/store and branch instructions 77

Name Effect Description
cbnz if Rt = 0 then Conditionally branch to label if Rt is
pc ← label nonzero.
end if
tbz if Rt[imm6] = 0 then Conditionally branch to label if the
pc ← label specified bit in Rt is zero.
end if
tbnz if Rt[imm6] = 0 then Conditionally branch to label if the
pc ← label specified bit in Rt is nonzero.
end if

3.5.4.3 Examples

The following program reads one character at a time until it reads in a character with an odd
ASCII value. For example, it will stop when it reads ‘a’ or ‘c’, which have ASCII values 97
and 99 respectively. When it reads an odd ASCII value, it stops and prints out the character,
then returns zero to its caller:

1 .section .rodata
2 format: .string "You entered an odd char: %c.\n"
3 .text
4 .type main, %function
5 .global main
6 main:
7 stp x29, x30, [sp, #-16]!
8
9 // do{c= getchar(); } while (c % 2 == 0)
10 loop:
11 bl getchar
12 tbz x0, #0, loop
13
14 // printf("You entered an odd char: %c\n", c)
15 mov x1, x0
16 ldr x0, =format
17 bl printf
18
19 // return 0
20 mov w0, #0
21 ldp x29, x30, [sp], #16
22 ret
23 .size main, (. - main)