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Annotation of OpenXM_contrib/gmp/mpn/x86/pentium/README, Revision 1.1.1.1

1.1       maekawa     1: This directory contains mpn functions optimized for Intel Pentium
                      2: processors.
                      3:
                      4: RELEVANT OPTIMIZATION ISSUES
                      5:
                      6: 1. Pentium doesn't allocate cache lines on writes, unlike most other modern
                      7: processors.  Since the functions in the mpn class do array writes, we have to
                      8: handle allocating the destination cache lines by reading a word from it in the
                      9: loops, to achieve the best performance.
                     10:
                     11: 2. Pairing of memory operations requires that the two issued operations refer
                     12: to different cache banks.  The simplest way to insure this is to read/write
                     13: two words from the same object.  If we make operations on different objects,
                     14: they might or might not be to the same cache bank.
                     15:
                     16: STATUS
                     17:
                     18: 1. mpn_lshift and mpn_rshift run at about 6 cycles/limb, but the Pentium
                     19: documentation indicates that they should take only 43/8 = 5.375 cycles/limb,
                     20: or 5 cycles/limb asymptotically.
                     21:
                     22: 2. mpn_add_n and mpn_sub_n run at asymptotically 2 cycles/limb.  Due to loop
                     23: overhead and other delays (cache refill?), they run at or near 2.5 cycles/limb.
                     24:
                     25: 3. mpn_mul_1, mpn_addmul_1, mpn_submul_1 all run 1 cycle faster than they
                     26: should...