1 ; vim:set ft=nasm:

2 segment code use32

3

4 ; void swap_buffers_asm(void *dest, void *src, int xsz, int ysz, int bpp)

5 ; dest -> eax

6 ; src -> edx

7 ; xsz -> ebx

8 ; ysz -> ecx

9 ; bpp -> [ebp + 8] (after pushing ebp)

10 global swap_buffers_asm_

11 swap_buffers_asm_:

12 push ebp

13 mov ebp, esp

14

15 mov edi, eax ; let's hold dest ptr in edi, frees up eax

16 mov esi, edx ; let's hold src ptr in esi, frees up edx

17 ; calculate pixel count -> ecx, frees up ebx

18 mov eax, ebx

19 mul ecx

20 mov ecx, eax ; now ecx = xsz * ysz

21

22 mov eax, [ebp + 8] ; eax <- bpp

23 cmp eax, 32

24 je .bpp32

25 cmp eax, 24

26 je .bpp24

27 cmp eax, 16

28 je .bpp16

29 ; invalid bpp, ignore

30 jmp .done

31

32 .bpp32: ; 32bit block transfer, no conversion

33 rep movsd ; esi, edi, and ecx already loaded, just go...

34 jmp .done

35

36 .bpp24: ; 32bpp -> 24bpp conversion (LSB-first), 1 byte overrun!

37 movsd ; transfer a full 32bit chunk and inc esi,edi by 4

38 dec edi ; backtrack dest one byte after last transfer

39 dec ecx

40 jnz .bpp24

41 jmp .done

42

43 .bpp16: ; fuck 16bpp for now (TODO)

44 .done:

45 pop ebp

46 ret