Guard out-of-range shift counts in integer opcodes#559
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The integer shift opcodes hand the per-element shift count straight to C++
<</>>. Whena<<bora>>bruns with a count that is negative or at least the operand width (32 for int, 64 for long long) the shift is undefined behavior. On arm64 `evaluate("a<<b")" with b=100 returns 80 because the hardware masks the count, while NumPy returns 0, and a UBSAN build traps right at the shift. Both int and long long, left and right, hit this.After the change an out-of-range left shift yields 0 and an out-of-range right shift clamps the count to width-1 so the sign bit fills, which is the result NumPy gives. The guard sits in the opcode next to the existing div/mod guards because the count is only known per element at run time, so a caller-side check could not cover array shift counts. Tradeoff is one extra unsigned compare per element; in-range counts keep the same value and the branch is well predicted.