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add some checks 

Even if they duplicate lower-level ones, we have an opportunity for better
error messages. Any time I see a hard-to-debug error message, I should
be asking myself, "what higher-level primitive should catch and improve
this error?"
This commit is contained in:
Kartik K. Agaram 2021-04-19 10:30:21 -07:00
parent f5ece0451b
commit 8e38b86ab0
1 changed files with 18 additions and 2 deletions
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500fake-screen.mu
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@ -151,13 +151,29 @@ fn draw-code-point screen: (addr screen), c: code-point, x: int, y: int, color:
# not really needed for a real screen, though it shouldn't do any harm
fn screen-cell-index _screen: (addr screen), x: int, y: int -> _/ecx: int {
var screen/esi: (addr screen) <- copy _screen
# only one bounds check isn't automatically handled
{
compare x, 0
break-if->=
abort "screen-cell-index: negative x"
}
{
var xmax/eax: (addr int) <- get screen, width
var xcurr/ecx: int <- copy x
compare xcurr, *xmax
break-if-<
abort "tried to print out of screen bounds"
abort "screen-cell-index: x too high"
}
{
compare y, 0
break-if->=
abort "screen-cell-index: negative y"
}
{
var ymax/eax: (addr int) <- get screen, width
var ycurr/ecx: int <- copy y
compare ycurr, *ymax
break-if-<
abort "screen-cell-index: y too high"
}
var width-addr/eax: (addr int) <- get screen, width
var result/ecx: int <- copy y