ev6-csum_ipv6_magic.S (5302B)
1/* SPDX-License-Identifier: GPL-2.0 */ 2/* 3 * arch/alpha/lib/ev6-csum_ipv6_magic.S 4 * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com> 5 * 6 * unsigned short csum_ipv6_magic(struct in6_addr *saddr, 7 * struct in6_addr *daddr, 8 * __u32 len, 9 * unsigned short proto, 10 * unsigned int csum); 11 * 12 * Much of the information about 21264 scheduling/coding comes from: 13 * Compiler Writer's Guide for the Alpha 21264 14 * abbreviated as 'CWG' in other comments here 15 * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html 16 * Scheduling notation: 17 * E - either cluster 18 * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1 19 * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1 20 * Try not to change the actual algorithm if possible for consistency. 21 * Determining actual stalls (other than slotting) doesn't appear to be easy to do. 22 * 23 * unsigned short csum_ipv6_magic(struct in6_addr *saddr, 24 * struct in6_addr *daddr, 25 * __u32 len, 26 * unsigned short proto, 27 * unsigned int csum); 28 * 29 * Swap <proto> (takes form 0xaabb) 30 * Then shift it left by 48, so result is: 31 * 0xbbaa0000 00000000 32 * Then turn it back into a sign extended 32-bit item 33 * 0xbbaa0000 34 * 35 * Swap <len> (an unsigned int) using Mike Burrows' 7-instruction sequence 36 * (we can't hide the 3-cycle latency of the unpkbw in the 6-instruction sequence) 37 * Assume input takes form 0xAABBCCDD 38 * 39 * Finally, original 'folding' approach is to split the long into 4 unsigned shorts 40 * add 4 ushorts, resulting in ushort/carry 41 * add carry bits + ushort --> ushort 42 * add carry bits + ushort --> ushort (in case the carry results in an overflow) 43 * Truncate to a ushort. (took 13 instructions) 44 * From doing some testing, using the approach in checksum.c:from64to16() 45 * results in the same outcome: 46 * split into 2 uints, add those, generating a ulong 47 * add the 3 low ushorts together, generating a uint 48 * a final add of the 2 lower ushorts 49 * truncating the result. 50 * 51 * Misalignment handling added by Ivan Kokshaysky <ink@jurassic.park.msu.ru> 52 * The cost is 16 instructions (~8 cycles), including two extra loads which 53 * may cause additional delay in rare cases (load-load replay traps). 54 */ 55 56#include <asm/export.h> 57 .globl csum_ipv6_magic 58 .align 4 59 .ent csum_ipv6_magic 60 .frame $30,0,$26,0 61csum_ipv6_magic: 62 .prologue 0 63 64 ldq_u $0,0($16) # L : Latency: 3 65 inslh $18,7,$4 # U : 0000000000AABBCC 66 ldq_u $1,8($16) # L : Latency: 3 67 sll $19,8,$7 # U : U L U L : 0x00000000 00aabb00 68 69 and $16,7,$6 # E : src misalignment 70 ldq_u $5,15($16) # L : Latency: 3 71 zapnot $20,15,$20 # U : zero extend incoming csum 72 ldq_u $2,0($17) # L : U L U L : Latency: 3 73 74 extql $0,$6,$0 # U : 75 extqh $1,$6,$22 # U : 76 ldq_u $3,8($17) # L : Latency: 3 77 sll $19,24,$19 # U : U U L U : 0x000000aa bb000000 78 79 cmoveq $6,$31,$22 # E : src aligned? 80 ldq_u $23,15($17) # L : Latency: 3 81 inswl $18,3,$18 # U : 000000CCDD000000 82 addl $19,$7,$19 # E : U L U L : <sign bits>bbaabb00 83 84 or $0,$22,$0 # E : 1st src word complete 85 extql $1,$6,$1 # U : 86 or $18,$4,$18 # E : 000000CCDDAABBCC 87 extqh $5,$6,$5 # U : L U L U 88 89 and $17,7,$6 # E : dst misalignment 90 extql $2,$6,$2 # U : 91 or $1,$5,$1 # E : 2nd src word complete 92 extqh $3,$6,$22 # U : L U L U : 93 94 cmoveq $6,$31,$22 # E : dst aligned? 95 extql $3,$6,$3 # U : 96 addq $20,$0,$20 # E : begin summing the words 97 extqh $23,$6,$23 # U : L U L U : 98 99 srl $18,16,$4 # U : 0000000000CCDDAA 100 or $2,$22,$2 # E : 1st dst word complete 101 zap $19,0x3,$19 # U : <sign bits>bbaa0000 102 or $3,$23,$3 # E : U L U L : 2nd dst word complete 103 104 cmpult $20,$0,$0 # E : 105 addq $20,$1,$20 # E : 106 zapnot $18,0xa,$18 # U : 00000000DD00BB00 107 zap $4,0xa,$4 # U : U U L L : 0000000000CC00AA 108 109 or $18,$4,$18 # E : 00000000DDCCBBAA 110 nop # E : 111 cmpult $20,$1,$1 # E : 112 addq $20,$2,$20 # E : U L U L 113 114 cmpult $20,$2,$2 # E : 115 addq $20,$3,$20 # E : 116 cmpult $20,$3,$3 # E : (1 cycle stall on $20) 117 addq $20,$18,$20 # E : U L U L (1 cycle stall on $20) 118 119 cmpult $20,$18,$18 # E : 120 addq $20,$19,$20 # E : (1 cycle stall on $20) 121 addq $0,$1,$0 # E : merge the carries back into the csum 122 addq $2,$3,$2 # E : 123 124 cmpult $20,$19,$19 # E : 125 addq $18,$19,$18 # E : (1 cycle stall on $19) 126 addq $0,$2,$0 # E : 127 addq $20,$18,$20 # E : U L U L : 128 /* (1 cycle stall on $18, 2 cycles on $20) */ 129 130 addq $0,$20,$0 # E : 131 zapnot $0,15,$1 # U : Start folding output (1 cycle stall on $0) 132 nop # E : 133 srl $0,32,$0 # U : U L U L : (1 cycle stall on $0) 134 135 addq $1,$0,$1 # E : Finished generating ulong 136 extwl $1,2,$2 # U : ushort[1] (1 cycle stall on $1) 137 zapnot $1,3,$0 # U : ushort[0] (1 cycle stall on $1) 138 extwl $1,4,$1 # U : ushort[2] (1 cycle stall on $1) 139 140 addq $0,$2,$0 # E 141 addq $0,$1,$3 # E : Finished generating uint 142 /* (1 cycle stall on $0) */ 143 extwl $3,2,$1 # U : ushort[1] (1 cycle stall on $3) 144 nop # E : L U L U 145 146 addq $1,$3,$0 # E : Final carry 147 not $0,$4 # E : complement (1 cycle stall on $0) 148 zapnot $4,3,$0 # U : clear upper garbage bits 149 /* (1 cycle stall on $4) */ 150 ret # L0 : L U L U 151 152 .end csum_ipv6_magic 153 EXPORT_SYMBOL(csum_ipv6_magic)