1 Copyright 2011 Free Software Foundation, Inc.
3 This file is part of the GNU MP Library.
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31 There are 5 generations of 64-but s390 processors, z900, z990, z9,
32 z10, and z196. The current GMP code was optimised for the two oldest,
38 This code makes use of a loop around MVC. It almost surely runs very
39 close to optimally. A small improvement could be done by using one
40 MVC for size 256 bytes, now we use two (we use an extra MVC when
41 copying any multiple of 256 bytes).
46 We have tried several feed-in variants here, branch tree, jump table
47 and computed goto. The fastest (on z990) turned out to be computed
50 An approach not tried is EX of LMG and STMG, modifying the register set
51 on-the-fly. Using that trick, we could completely avoid using
52 separate feed-in paths.
55 mpn_lshift, mpn_rshift
57 The current code runs at pipeline decode bandwidth on z990.
62 The current code is 4-way unrolled. It should be unrolled more, at
63 least 8x, in order to reach 2.5 c/l.
66 mpn_mul_1, mpn_addmul_1, mpn_submul_1
68 The current code is very naive, but due to the non-pipelined nature of
69 MLGR on z900 and z990, more sophisticated code would not gain much.
71 On z10 one would need to cluster at least 4 MLGR together, in order to
74 On z196, one surely want to use unrolling and pipelining, to perhaps
75 reach around 12 c/l. A major issue here and on z10 is ALCGR's 3 cycle
79 mpn_mul_2, mpn_addmul_2
81 At least for older machines (z900, z990) with very slow MLGR, we
82 should use Karatsuba's algorithm on 2-limb units, making mul_2 and
83 addmul_2 the main multiplication primitives. The newer machines might
84 benefit less from this approach, perhaps in particular z10, where MLGR
85 clustering is more important.
87 With Karatsuba, one could hope for around 16 cycles per accumulated
88 128 cross product, on z990.