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Comment by niggler | Hacker News Reader

Interesting that NaCl is far closer to native performance than asm.js. Can that performance gap be closed?

I'm not sure I'd call that "far" different, but asm.js is certainly in early stages so it probably will get faster.

    C (gcc 4.2.1)	2.62 +/- 0.24	1.0x
    NaCl (x86-32)	3.39 +/- 0.25	1.3x
    asm.js (Firefox Nightly)	5.12 +/- 0.59	1.9x

NaCl is 30% slower, asm.js is 90% slower.

Your conclusion doesn't follow from your data. 5.12 is not 90% slower than 2.62, it's 51% slower.

He says NaCl is 30% slower than _c++_, asm.js is 90% slower than _c++_ which is correct.

For asm.js to be 90% slower than c++, it would have to run at 10% the speed of c++, not 51% of its speed, which is what the data shows. 100% slower is not 1/2 the speed, it's no speed at all.

Take some speed x. Increasing it by 100% gives 2x. Decreasing it by 100% gives zero.

Expressed another way, 100% of x is x. Add 100% = 2x, Subtract 100% = zero. The original claim is "90% slower." Clearly the OP either meant 51% slower or 49% slower, depending on how one reads it.

a = 2.62

b = 5.19

a / b = 0.5048, or 50.48%: "b has 50.48 percent the speed of a".

EDIT: wow, once again downvoted for being right and proving it.

English conventions are inconsistent. "X is 2x slower than Y" usually means that Y runs at twice the speed of X. Since 90% = 0.9, "X is 90% slower than Y" would mean that X is actually faster than Y. Therefore it's better to state it in an unambiguous way, e.g. X took 2x as much time as Y, or just look at the numbers directly.

> English conventions are inconsistent.

Yes, and it's an argument for expressing these ideas with mathematics instead of words.

> Therefore it's better to state it in an unambiguous way, e.g. X took 2x as much time as Y, or just look at the numbers directly.

Complete agreement.

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