Soul of a tiny new machine. More thorough tests → More comprehensible and rewrite-friendly software → More resilient society.
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# Primitives for screen control.
#
# We need to do this in machine code because Mu doesn't have global variables
# yet (for the start of video memory).
== code
pixel-on-real-screen: # x: int, y: int, color: int
# . prologue
55/push-ebp
89/<- %ebp 4/r32/esp
#
(pixel-on-screen-buffer *Video-memory-addr *(ebp+8) *(ebp+0xc) *(ebp+0x10) 0x400 0x300)
$pixel-on-real-screen:end:
# . epilogue
89/<- %esp 5/r32/ebp
5d/pop-to-ebp
c3/return
# 'buffer' here is not a valid Mu type: a naked address without a length.
pixel-on-screen-buffer: # buffer: (addr byte), x: int, y: int, color: int, width: int, height: int
# . prologue
55/push-ebp
89/<- %ebp 4/r32/esp
# . save registers
50/push-eax
51/push-ecx
# bounds checks
8b/-> *(ebp+0xc) 0/r32/eax # foo
3d/compare-eax-and 0/imm32
7c/jump-if-< $pixel-on-screen-buffer:end/disp8
3b/compare 0/r32/eax *(ebp+0x18)
7d/jump-if->= $pixel-on-screen-buffer:end/disp8
8b/-> *(ebp+0x10) 0/r32/eax
3d/compare-eax-and 0/imm32
7c/jump-if-< $pixel-on-screen-buffer:end/disp8
3b/compare 0/r32/eax *(ebp+0x1c)
7d/jump-if->= $pixel-on-screen-buffer:end/disp8
# eax = y*width + x
8b/-> *(ebp+0x10) 0/r32/eax
0f af/multiply-> *(ebp+0x18) 0/r32/eax
03/add-> *(ebp+0xc) 0/r32/eax
# eax += location of frame buffer
03/add-> *(ebp+8) 0/r32/eax
# *eax = color
8b/-> *(ebp+0x14) 1/r32/ecx
88/byte<- *eax 1/r32/CL
$pixel-on-screen-buffer:end:
# . restore registers
59/pop-to-ecx
58/pop-to-eax
# . epilogue
89/<- %esp 5/r32/ebp
5d/pop-to-ebp
c3/return