path: root/contrib/libgmp/mpn/sparc32/README
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This directory contains mpn functions for various SPARC chips.  Code that
runs only on version 8 SPARC implementations, is in the v8 subdirectory.


  Load and Store timing

On most early SPARC implementations, the ST instructions takes multiple
cycles, while a STD takes just a single cycle more than an ST.  For the CPUs
in SPARCstation I and II, the times are 3 and 4 cycles, respectively.
Therefore, combining two ST instrucitons into a STD when possible is a
significant optimiation.

Later SPARC implementations have single cycle ST.

For SuperSPARC, we can perform just one memory instruction per cycle, even
if up to two integer instructions can be executed in its pipeline.  For
programs that perform so many memory operations that there are not enough
non-memory operations to issue in parallel with all memory operations, using
LDD and STD when possible helps.


1. On a SuperSPARC, mpn_lshift and mpn_rshift run at 3 cycles/limb, or 2.5
   cycles/limb asymptotically.  We could optimize speed for special counts
   by using ADDXCC.

2. On a SuperSPARC, mpn_add_n and mpn_sub_n runs at 2.5 cycles/limb, or 2
   cycles/limb asymptotically.

3. mpn_mul_1 runs at what is believed to be optimal speed.

4. On SuperSPARC, mpn_addmul_1 and mpn_submul_1 could both be improved by a
   cycle by avoiding one of the add instrucitons.  See a29k/addmul_1.

The speed of the code for other SPARC implementations is uncertain.