README revision 1.1.1.2
1 1.1 mrg Copyright 1999, 2001, 2002, 2004 Free Software Foundation, Inc. 2 1.1 mrg 3 1.1 mrg This file is part of the GNU MP Library. 4 1.1 mrg 5 1.1 mrg The GNU MP Library is free software; you can redistribute it and/or modify 6 1.1.1.2 mrg it under the terms of either: 7 1.1.1.2 mrg 8 1.1.1.2 mrg * the GNU Lesser General Public License as published by the Free 9 1.1.1.2 mrg Software Foundation; either version 3 of the License, or (at your 10 1.1.1.2 mrg option) any later version. 11 1.1.1.2 mrg 12 1.1.1.2 mrg or 13 1.1.1.2 mrg 14 1.1.1.2 mrg * the GNU General Public License as published by the Free Software 15 1.1.1.2 mrg Foundation; either version 2 of the License, or (at your option) any 16 1.1.1.2 mrg later version. 17 1.1.1.2 mrg 18 1.1.1.2 mrg or both in parallel, as here. 19 1.1 mrg 20 1.1 mrg The GNU MP Library is distributed in the hope that it will be useful, but 21 1.1 mrg WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 22 1.1.1.2 mrg or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 23 1.1.1.2 mrg for more details. 24 1.1 mrg 25 1.1.1.2 mrg You should have received copies of the GNU General Public License and the 26 1.1.1.2 mrg GNU Lesser General Public License along with the GNU MP Library. If not, 27 1.1.1.2 mrg see https://www.gnu.org/licenses/. 28 1.1 mrg 29 1.1 mrg 30 1.1 mrg 31 1.1 mrg 32 1.1 mrg This directory contains mpn functions for 64-bit PA-RISC 2.0. 33 1.1 mrg 34 1.1 mrg PIPELINE SUMMARY 35 1.1 mrg 36 1.1 mrg The PA8x00 processors have an orthogonal 4-way out-of-order pipeline. Each 37 1.1 mrg cycle two ALU operations and two MEM operations can issue, but just one of the 38 1.1 mrg MEM operations may be a store. The two ALU operations can be almost any 39 1.1 mrg combination of non-memory operations. Unlike every other processor, integer 40 1.1 mrg and fp operations are completely equal here; they both count as just ALU 41 1.1 mrg operations. 42 1.1 mrg 43 1.1 mrg Unfortunately, some operations cause hickups in the pipeline. Combining 44 1.1 mrg carry-consuming operations like ADD,DC with operations that does not set carry 45 1.1 mrg like ADD,L cause long delays. Skip operations also seem to cause hickups. If 46 1.1 mrg several ADD,DC are issued consecutively, or if plain carry-generating ADD feed 47 1.1 mrg ADD,DC, stalling does not occur. We can effectively issue two ADD,DC 48 1.1 mrg operations/cycle. 49 1.1 mrg 50 1.1 mrg Latency scheduling is not as important as making sure to have a mix of ALU and 51 1.1 mrg MEM operations, but for full pipeline utilization, it is still a good idea to 52 1.1 mrg do some amount of latency scheduling. 53 1.1 mrg 54 1.1 mrg Like for all other processors, RAW memory scheduling is critically important. 55 1.1 mrg Since integer multiplication takes place in the floating-point unit, the GMP 56 1.1 mrg code needs to handle this problem frequently. 57 1.1 mrg 58 1.1 mrg STATUS 59 1.1 mrg 60 1.1 mrg * mpn_lshift and mpn_rshift run at 1.5 cycles/limb on PA8000 and at 1.0 61 1.1 mrg cycles/limb on PA8500. With latency scheduling, the numbers could 62 1.1 mrg probably be improved to 1.0 cycles/limb for all PA8x00 chips. 63 1.1 mrg 64 1.1 mrg * mpn_add_n and mpn_sub_n run at 2.0 cycles/limb on PA8000 and at about 65 1.1 mrg 1.6875 cycles/limb on PA8500. With latency scheduling, this could 66 1.1 mrg probably be improved to get close to 1.5 cycles/limb. A problem is the 67 1.1 mrg stalling of carry-inputting instructions after instructions that do not 68 1.1 mrg write to carry. 69 1.1 mrg 70 1.1 mrg * mpn_mul_1, mpn_addmul_1, and mpn_submul_1 run at between 5.625 and 6.375 71 1.1 mrg on PA8500 and later, and about a cycle/limb slower on older chips. The 72 1.1 mrg code uses ADD,DC for adjacent limbs, and relies heavily on reordering. 73 1.1 mrg 74 1.1 mrg 75 1.1 mrg REFERENCES 76 1.1 mrg 77 1.1 mrg Hewlett Packard, "64-Bit Runtime Architecture for PA-RISC 2.0", version 3.3, 78 1.1 mrg October 1997. 79
Indexes created Sun Jun 07 00:24:08 UTC 2026