fix: Clamp both of range's endpoints before subtracting - #220
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SamuelSchlesinger wants to merge 2 commits into
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fix: Clamp both of range's endpoints before subtracting#220SamuelSchlesinger wants to merge 2 commits into
SamuelSchlesinger wants to merge 2 commits into
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range clips the start against [0, rows] and the length against [0, rows] independently, instead of clipping the length against the rows that remain after the start. An end past the last row slices out of bounds (range (8, 20) on ten rows dies with "invalid slice (8,10,10)"), and a negative start stretches the slice by the underflow (range (-5, 3) returns eight rows instead of three). Subtracting before clamping also wraps: range (1, minBound) reopens the range instead of emptying it. The property covers arbitrary endpoints, with an oracle that clamps before it subtracts for the same reason.
The start and the length were clipped against the row count independently, so an end past the last row produced a slice running off the end of the column and a negative start widened the slice by the underflow. Subtracting first also let a very negative end wrap to a large positive length. Clamp the start, then the end against it, and take the difference.
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rangeclampedstartandend - startseparately, sorange (8, 20)on a 10-row frame reports 10 rows and throwsinvalid slice (8,10,10)as soon as a column is forced, andrange (1, minBound)overflows into the same 10-row slice instead of an empty frame. Clamp both endpoints, then subtract.Adds a QuickCheck property against a clamp-first oracle plus three unit cases.