Page 162 - ARM 64 Bit Assembly Language

148 Chapter 5

Listing 5.40 Improved initialization in assembly.

1 .equ i_red, 0
2 .equ i_green, 1
3 .equ i_blue, 2
4 .equ i_size, 3
5 .equ width, 100
6 .equ height, 100
7
8 .text
9 .type main, %function
10 .global main
11 main: stp x29, x30, [sp, #-16]!
12 // Call malloc to allocate the array of pixels
13 mov x0, #(width*height*i_size) // calculate space needed
14 bl malloc // allocate storage.
15 cmp x0, #0 // if (image != NULL)
16 bne endif // goto endif
17 mov w0, #1 // else return 1
18 b return
19 endif: mov w2, #(width*height*i_size) // w2=w*h* size
20 mov w3, #0 // w3 = 0
21 mov w1, #0 // inti=0
22 loop: add x9, x1, x0 // x9 = image + i
23 strb w3, [x9, #i_red] // image[i].red = 0
24 strb w3, [x9, #i_green] // image[i].green = 0
25 strb w3, [x9, #i_blue] // image[i].blue = 0
26 add w1, w1, #3 // i += 3
27 cmp w1, w2 // if(i<width*height*3)
28 blt loop // repeat loop
29
30 bl free // free(image)
31 mov w0, #0 // return 0
32 return: ldp x29, x30, [sp], #16
33 ret
34 .size main, (. - main)

results of these additional improvements. This third implementation will run much faster than
the previous implementations on a very large array, or image.

5.6 Chapter summary

Spaghetti code is the bane of assembly programming, but it can easily be avoided. Although
assembly language does not enforce structured programming, it does provide the low-level