optimizing javascript

optimizing a range coder
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- Instead of Math.floor(a / b), use (a / b) | 0.  Only works if you need signed integers.  If you need unsigned, have to compare < 0
- Instead of ((a & 0xFFFFFF) * 256), use, a <<= 8; if (a < 0) a += 0x100000000;
- Constants don't need to be hardcoded most of the time
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