Hi,

Since all computer has SSE2, now, using standard math function (cmath) still needed ?

Is it correct to do all using SSE2 ? AVX is young but now SSE2 is here since a long time.

Not all CPUs have SSE2. However, you might not be targeting "all CPUs" with your program. Yes, nearly all personal computers have SSE2 support these days, but there's a good number of devices (like cell phones, RPis, etc.) that don't support SSE2. So it depends on what kind of computers you are targeting, and I'm not sure what that is. It's up to you.

But of course, the cmath functions, plus your compiler's optimizer, very well might be using SSE2 anyway...

If you're making a game for Windows PCs, you can just assume that the user will have SSE2, and write on your box/manual/website that an SSE2 CPU is required (basically: Pentium 4 or newer).

On other platforms, there might be different SIMD instruction sets other than SSE/AVX -- e.g. ARM CPUs have NEON and PPC have AltiVec.

However, using on x86/PC, it's not always best to use SSE, because mixing float and SSE code is slow. Within a particular bit of code (e.g. a particle simulation), you either need all of your code to use float, or all of it to use SSE.

If some of the code is float, and some is SSE, then data needs to be transferred from the SSE registers to the float registers (or vice versa) -- in order to do this, the CPU needs to write the data from one type of register to RAM, then read it from RAM to the other type of register. This can be extremely slow.