3 ms·

I suppose what they referred to is Java's (currently incubating) vector computation API. It lets you express vectorized algorithms in high-level way, with the A

I suppose what they referred to is Java's (currently incubating) vector computation API. It lets you express vectorized algorithms in high-level way, with the API's methods being translated of the corresponding SIMD instructions of the underlying platform. I.e. you'll get vectorized execution on x86 and AArch-64 in a portable way, including transparent fallback to scalar execution if specific operations aren't supported on a specific target platform.

Jensson 5y ago
Right, but that would still mean that C is closer to the hardware than Java. Java has a high level but less powerful solution, since you can only use it on vectors and not arbitrary data anywhere. You can write a similar function in C which compiles differently depending on where you compile and falls back in the same way, just that C gives you the option to use the hardware dependent instructions anywhere if you want.
- kaba0 5y ago
  I’m not sure I understand you: in C there is no standard way for SIMD afaik. There are pragmas on for loops, or other compiler specific tools but the language itself don’t have any notion of lanes or SIMD instructions.
  - Jensson 5y ago
    > but the language itself don’t have any notion of lanes or SIMD instructions. C doesn't need it, you can just call CPU instructions like functions. SIMD is just another kind of CPU instruction, so C supports it. That works in C since you have a direct view of the memory layout. It doesn't work in higher level languages where memory is abstracted away from you, in those you need the higher level concepts you are talking about in order to take advantage of SIMD.
    - gunnarmorling 5y ago
      These instructions are ISA specific though; i.e. in C you'd have to implement your solution once using x86 SIMD instructions and once using the AArch64 counterparts. You'd also have to account for different vector lengths. Whereas the Java API does all that for you automatically, e.g. automatically taking advantage of longer vectors when running on AVX512, and shorter ones elsewhere. I think that's what people consider "better" about the Java approach (at least I do). That's of course not to say that you cannot do all this in C as well, but I think having these capabilities in that portable way available in Java makes SIMD useable for a huge audience for the first time which didn't consider that a realistic option before.

Jensson 5y ago

Right, but that would still mean that C is closer to the hardware than Java. Java has a high level but less powerful solution, since you can only use it on vectors and not arbitrary data anywhere. You can write a similar function in C which compiles differently depending on where you compile and falls back in the same way, just that C gives you the option to use the hardware dependent instructions anywhere if you want.

kaba0 5y ago
I’m not sure I understand you: in C there is no standard way for SIMD afaik. There are pragmas on for loops, or other compiler specific tools but the language itself don’t have any notion of lanes or SIMD instructions.
- Jensson 5y ago
  > but the language itself don’t have any notion of lanes or SIMD instructions. C doesn't need it, you can just call CPU instructions like functions. SIMD is just another kind of CPU instruction, so C supports it. That works in C since you have a direct view of the memory layout. It doesn't work in higher level languages where memory is abstracted away from you, in those you need the higher level concepts you are talking about in order to take advantage of SIMD.
  - gunnarmorling 5y ago
    These instructions are ISA specific though; i.e. in C you'd have to implement your solution once using x86 SIMD instructions and once using the AArch64 counterparts. You'd also have to account for different vector lengths. Whereas the Java API does all that for you automatically, e.g. automatically taking advantage of longer vectors when running on AVX512, and shorter ones elsewhere. I think that's what people consider "better" about the Java approach (at least I do). That's of course not to say that you cannot do all this in C as well, but I think having these capabilities in that portable way available in Java makes SIMD useable for a huge audience for the first time which didn't consider that a realistic option before.