JavaScript: Efficient integer arithmetic

Question

I'm currently writing a compiler for a small language that compiles to JavaScript. In this language, I'd quite like to have integers, but JavaScript only supports Number, which is a double-precision floating point value. So, what's the most efficient way to implement integers in JavaScript? And how efficient is this compared to just using Number?

In particular, overflow behaviour should be consistent with other languages: for instance, adding one to INT_MAX should give INT_MIN. Integers should either be 32-bit or 64-bit.

Answer 1

So, what's the most efficient way to implement integers in JavaScript?

The primitive number type is as efficient as it gets. Many modern JS engines support JIT compilation, so it should be almost as efficient as native floating-point arithmetic.

In particular, overflow behaviour should be consistent with other languages: for instance, adding one to INT_MAX should give INT_MIN. Integers should either be 32-bit or 64-bit.

You can achieve the semantics of standard 32-bit integer arithmetic by noting that JavaScript converts "numbers" to 32-bit integers for bitwise operations. >>> (unsigned right shift) converts its operand to an unsigned 32-bit integer while the rest (all other shifts and bitwise AND/OR) convert their operand to a signed 32-bit integer. For example:

• 0xFFFFFFFF | 0 yields -1 (signed cast)
• (0xFFFFFFFF + 1) | 0 yields 0 (overflow)
• -1 >>> 0 yields 0xFFFFFFFF (unsigned cast)