1 Copyright 1999-2001, 2003-2005 Free Software Foundation, Inc.
3 This file is part of the GNU MP Library.
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14 * the GNU General Public License as published by the Free Software
15 Foundation; either version 2 of the License, or (at your option) any
18 or both in parallel, as here.
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21 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
22 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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31 POWERPC-64 MPN SUBROUTINES
34 This directory contains mpn functions for 64-bit PowerPC chips.
39 mpn/powerpc64 mode-neutral code
40 mpn/powerpc64/mode32 code for mode32
41 mpn/powerpc64/mode64 code for mode64
44 The mode32 and mode64 sub-directories contain code which is for use in the
45 respective chip mode, 32 or 64. The top-level directory is code that's
46 unaffected by the mode.
48 The "adde" instruction is the main difference between mode32 and mode64. It
49 operates on either on a 32-bit or 64-bit quantity according to the chip mode.
50 Other instructions have an operand size in their opcode and hence don't vary.
54 POWER3/PPC630 pipeline information:
56 Decoding is 4-way + branch and issue is 8-way with some out-of-order
62 FXU1 - integer unit 1, handles any simple integer instruction
63 FXU2 - integer unit 2, handles any simple integer instruction
64 FXU3 - integer unit 3, handles integer multiply and divide
65 FPU1 - floating-point unit 1
66 FPU2 - floating-point unit 2
68 Memory: Any two memory operations can issue, but memory subsystem
69 can sustain just one store per cycle. No need for data
70 prefetch; the hardware has very sophisticated prefetch logic.
71 Simple integer: 2 operations (such as add, rl*)
72 Integer multiply: 1 operation every 9th cycle worst case; exact timing depends
73 on 2nd operand's most significant bit position (10 bits per
74 cycle). Multiply unit is not pipelined, only one multiply
75 operation in progress is allowed.
77 Floating-point: Any plain 2 arithmetic instructions (such as fmul, fadd, and
78 fmadd), latency 4 cycles.
79 Floating-point divide:
81 Floating-point square root:
84 POWER3/PPC630 best possible times for the main loops:
85 shift: 1.5 cycles limited by integer unit contention.
86 With 63 special loops, one for each shift count, we could
87 reduce the needed integer instructions to 2, which would
88 reduce the best possible time to 1 cycle.
89 add/sub: 1.5 cycles, limited by ld/st unit contention.
90 mul: 18 cycles (average) unless floating-point operations are used,
91 but that would only help for multiplies of perhaps 10 and more
93 addmul/submul:Same situation as for mul.
96 POWER4/PPC970 and POWER5 pipeline information:
98 This is a very odd pipeline, it is basically a VLIW masquerading as a plain
99 architecture. Its issue rules are not made public, and since it is so weird,
100 it is very hard to figure out any useful information from experimentation.
103 A well-aligned loop with nop's take 3, 4, 6, 7, ... cycles.
104 3 cycles for 0, 1, 2, 3, 4, 5, 6, 7 nop's
105 4 cycles for 8, 9, 10, 11, 12, 13, 14, 15 nop's
106 6 cycles for 16, 17, 18, 19, 20, 21, 22, 23 nop's
107 7 cycles for 24, 25, 26, 27 nop's
108 8 cycles for 28, 29, 30, 31 nop's
109 ... continues regularly
115 FXU1 - integer unit 1, handles any integer instruction
116 FXU2 - integer unit 2, handles any integer instruction
117 FPU1 - floating-point unit 1
118 FPU2 - floating-point unit 2
120 While this is one integer unit less than POWER3/PPC630, the remaining units
121 are more powerful; here they handle multiply and divide.
123 Memory: 2 ld/st. Stores go to the L2 cache, which can sustain just
125 L1 load latency: to gregs 3-4 cycles, to fregs 5-6 cycles.
126 Operations that modify the address register might be split
127 to use also an integer issue slot.
128 Simple integer: 2 operations every cycle, latency 2.
129 Integer multiply: 2 operations every 6th cycle, latency 7 cycles.
131 Floating-point: Any plain 2 arithmetic instructions (such as fmul, fadd, and
132 fmadd), latency 6 cycles.
133 Floating-point divide:
135 Floating-point square root:
141 *mul_1: Handling one limb using mulld/mulhdu and two limbs using floating-
142 point operations should give performance of about 20 cycles for 3 limbs, or 7
145 We should probably split the single-limb operand in 32-bit chunks, and the
146 multi-limb operand in 16-bit chunks, allowing us to accumulate well in fp
149 Problem is to get 32-bit or 16-bit words to the fp registers. Only 64-bit fp
150 memops copies bits without fiddling with them. We might therefore need to
151 load to integer registers with zero extension, store as 64 bits into temp
152 space, and then load to fp regs. Alternatively, load directly to fp space
153 and add well-chosen constants to get cancellation. (Other part after given by
154 subsequent subtraction.)
156 Possible code mix for load-via-intregs variant:
159 fmadd,fmadd,fmul,fmul
160 fctidz,stfd,ld,fctidz,stfd,ld
163 fmadd,fmadd,fmul,fmul
164 fctidz,stfd,ld,fctidz,stfd,ld
166 srd,sld,add,adde,add,adde