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# Primitives for screen control.
== code
pixel: # screen: (addr screen), x: int, y: int, color: int
# . prologue
55/push-ebp
89/<- %ebp 4/r32/esp
# . save registers
50/push-eax
51/push-ecx
# ecx = screen
8b/-> *(ebp+8) 1/r32/ecx
81 7/subop/compare %ecx 0/imm32
{
75/jump-if-!= break/disp8
# bounds checks
8b/-> *(ebp+0xc) 0/r32/eax
3d/compare-eax-and 0/imm32
7c/jump-if-< $pixel:end/disp8
3d/compare-eax-and 0x400/imm32/1024
7d/jump-if->= $pixel:end/disp8
8b/-> *(ebp+0x10) 0/r32/eax
3d/compare-eax-and 0/imm32
7c/jump-if-< $pixel:end/disp8
3d/compare-eax-and 0x300/imm32/768
7d/jump-if->= $pixel:end/disp8
# eax = y*1024 + x
8b/-> *(ebp+0x10) 0/r32/eax
c1/shift 4/subop/left %eax 0xa/imm8
03/add-> *(ebp+0xc) 0/r32/eax
# eax += location of frame buffer
03/add-> *0x7f28 0/r32/eax
# *eax = color
8b/-> *(ebp+0x14) 1/r32/ecx
88/byte<- *eax 1/r32/CL
# return
eb $pixel:end/disp8
}
# TODO: fake screen
$pixel:end:
# . restore registers
59/pop-to-ecx
58/pop-to-eax
# . epilogue
89/<- %esp 5/r32/ebp
5d/pop-to-ebp
c3/return
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