Hello, Bill. You wrote 22 июня 2010 г., 3:30:30: > BSDNT > ...... > scratch. One idea I had was to write all the low level routines in > LLVM instead of assembly, then just build suitable optimisations into > LLVM so that nice assembly is automatically produced. This is entirely > feasible and would mean only one lot of low level routines would ever > need to be written, rather than a different set for each platform > ..... > However, LLVM doesn't support carry propagation well
Automatic translation like that (ALGLIB project) saves me a lot of time. Implementing things twice is twice as hard as implementing them once. But implementing then 10 times would be 10^2 times harder. So using LLBM is a great idea, but lack of carry propagation is a serious drawback. I think it is possible to extend LLVM with carry support, but it will require too much time. What do you think about another idea (which came from numerical linear algebra)? It is called 'blocking'. In principle all your library could be written entirely in C, but it can't because C doesn't supports operations with limbs with carry propagation. The only thing you need to have efficient library is to have efficient add/sub/mul/div for limbs (single limbs, not sequences of limbs), right? Imagine library with limbs which are 1024 bytes long. You just have to code in assembler only four operations: add two limbs (with optional carry), sub two limbs, mul two limbs, div two limbds. Implement them as separate functions. Then you can write "generic C" library which calls these functions instead of using arithmetic operators provides by language like + or *. You have to write only four functions, and now you have efficient mpn_add_n, mpn_add_1, mpn_add, mpn_sub_n, etc. And these mpn functions will be written entirely in C. Of course, you will have function call penalty, but it should become less significant with such large limbs. As in numerical linear algebra. What do you think about it? -- With best regards, Sergey mailto:sergey.bochka...@alglib.net -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
