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Chris Tate
0af86e2e3e
A loop with two counters closing in on each other, such as `for (let i = lo, j = hi; i < j; i++, j--)`, checked the bounds of every typed-array element it read or wrote at either counter. Within the body the low counter only rises and stays below the high one, which only falls, so every such index lies between the two starts. Typed-array loop versions now cover these loops. The guard tests that both starts are exact integers, that the low start is at least 0, and that the high start is below the length of each view the loop indexes at a counter. The fast copy then reads and writes those elements without checks, and the checked copy runs whenever the guard fails. In the fast copy the guard also stands for the loop's own start test. The exact-integer test of a start is now one function, shared by the typed-array version guards and the dense array two-counter guard. The dense guard, which compared the round trip with `fcmp oeq`, now also leaves a -0 start to the checked loop.