1 | $NetBSD: oc_cksum.s,v 1.11 2023/09/26 14:33:55 tsutsui Exp $ 2 3 | Copyright (c) 1988 Regents of the University of California. 4 | All rights reserved. 5 | 6 | Redistribution and use in source and binary forms, with or without 7 | modification, are permitted provided that the following conditions 8 | are met: 9 | 1. Redistributions of source code must retain the above copyright 10 | notice, this list of conditions and the following disclaimer. 11 | 2. Redistributions in binary form must reproduce the above copyright 12 | notice, this list of conditions and the following disclaimer in the 13 | documentation and/or other materials provided with the distribution. 14 | 3. Neither the name of the University nor the names of its contributors 15 | may be used to endorse or promote products derived from this software 16 | without specific prior written permission. 17 | 18 | THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19 | ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 | IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 | ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22 | FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 | DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24 | OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25 | HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 | LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 | OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28 | SUCH DAMAGE. 29 | 30 | @(#)oc_cksum.s 7.2 (Berkeley) 11/3/90 31 | 32 | 33 | oc_cksum: ones complement 16 bit checksum for MC68020. 34 | 35 | oc_cksum (buffer, count, strtval) 36 | 37 | Do a 16 bit one's complement sum of 'count' bytes from 'buffer'. 38 | 'strtval' is the starting value of the sum (usually zero). 39 | 40 | It simplifies life in in_cksum if strtval can be >= 2^16. 41 | This routine will work as long as strtval is < 2^31. 42 | 43 | Performance 44 | ----------- 45 | This routine is intended for MC 68020s but should also work 46 | for 68030s. It (deliberately) doesn't worry about the alignment 47 | of the buffer so will only work on a 68010 if the buffer is 48 | aligned on an even address. (Also, a routine written to use 49 | 68010 "loop mode" would almost certainly be faster than this 50 | code on a 68010). 51 | 52 | We don't worry about alignment because this routine is frequently 53 | called with small counts: 20 bytes for IP header checksums and 40 54 | bytes for TCP ack checksums. For these small counts, testing for 55 | bad alignment adds ~10% to the per-call cost. Since, by the nature 56 | of the kernel's allocator, the data we're called with is almost 57 | always longword aligned, there is no benefit to this added cost 58 | and we're better off letting the loop take a big performance hit 59 | in the rare cases where we're handed an unaligned buffer. 60 | 61 | Loop unrolling constants of 2, 4, 8, 16, 32 and 64 times were 62 | tested on random data on four different types of processors (see 63 | list below -- 64 was the largest unrolling because anything more 64 | overflows the 68020 Icache). On all the processors, the 65 | throughput asymptote was located between 8 and 16 (closer to 8). 66 | However, 16 was substantially better than 8 for small counts. 67 | (It's clear why this happens for a count of 40: unroll-8 pays a 68 | loop branch cost and unroll-16 doesn't. But the tests also showed 69 | that 16 was better than 8 for a count of 20. It's not obvious to 70 | me why.) So, since 16 was good for both large and small counts, 71 | the loop below is unrolled 16 times. 72 | 73 | The processors tested and their average time to checksum 1024 bytes 74 | of random data were: 75 | Sun 3/50 (15MHz) 190 us/KB 76 | Sun 3/180 (16.6MHz) 175 us/KB 77 | Sun 3/60 (20MHz) 134 us/KB 78 | Sun 3/280 (25MHz) 95 us/KB 79 | 80 | The cost of calling this routine was typically 10% of the per- 81 | kilobyte cost. E.g., checksumming zero bytes on a 3/60 cost 9us 82 | and each additional byte cost 125ns. With the high fixed cost, 83 | it would clearly be a gain to "inline" this routine -- the 84 | subroutine call adds 400% overhead to an IP header checksum. 85 | However, in absolute terms, inlining would only gain 10us per 86 | packet -- a 1% effect for a 1ms ethernet packet. This is not 87 | enough gain to be worth the effort. 88 89 #include <m68k/asm.h> 90 91 .text 92 93 ENTRY(oc_cksum) 94 movl 4(%sp),%a0 | get buffer ptr 95 movl 8(%sp),%d1 | get byte count 96 movl 12(%sp),%d0 | get starting value 97 movl %d2,-(%sp) | free a reg 98 99 | test for possible 1, 2 or 3 bytes of excess at end 100 | of buffer. The usual case is no excess (the usual 101 | case is header checksums) so we give that the faster 102 | 'not taken' leg of the compare. (We do the excess 103 | first because we're about the trash the low order 104 | bits of the count in d1.) 105 106 btst #0,%d1 107 jne .L5 | if one or three bytes excess 108 btst #1,%d1 109 jne .L7 | if two bytes excess 110 .L1: 111 #ifdef __mcoldfire__ 112 movq #-4,%d2 | mask to clear bottom two bits 113 andl %d2,%d1 | longword truncate length 114 movl %d1,%d2 | move length to d2 115 movl %d1,%a1 | move length to a1 116 addl %a0,%a1 | add start so a1 now points to end 117 movq #0x3c,%d1 | then find fractions of a chunk 118 andl %d1,%d2 119 negl %d2 120 subl %d1,%d1 | this can never carry so X is cleared 121 #else 122 movl %d1,%d2 | move to d2 123 lsrl #6,%d1 | make cnt into # of 64 byte chunks 124 andl #0x3c,%d2 | then find fractions of a chunk 125 negl %d2 126 andb #0xf,%cc | clear X 127 #endif 128 jmp (.L3-.-2:b,%pc,%d2) 129 .L2: 130 movl (%a0)+,%d2 131 addxl %d2,%d0 132 movl (%a0)+,%d2 133 addxl %d2,%d0 134 movl (%a0)+,%d2 135 addxl %d2,%d0 136 movl (%a0)+,%d2 137 addxl %d2,%d0 138 movl (%a0)+,%d2 139 addxl %d2,%d0 140 movl (%a0)+,%d2 141 addxl %d2,%d0 142 movl (%a0)+,%d2 143 addxl %d2,%d0 144 movl (%a0)+,%d2 145 addxl %d2,%d0 146 movl (%a0)+,%d2 147 addxl %d2,%d0 148 movl (%a0)+,%d2 149 addxl %d2,%d0 150 movl (%a0)+,%d2 151 addxl %d2,%d0 152 movl (%a0)+,%d2 153 addxl %d2,%d0 154 movl (%a0)+,%d2 155 addxl %d2,%d0 156 movl (%a0)+,%d2 157 addxl %d2,%d0 158 movl (%a0)+,%d2 159 addxl %d2,%d0 160 movl (%a0)+,%d2 161 addxl %d2,%d0 162 .L3: 163 #ifdef __mcoldfire__ 164 cmpal %a0,%a1 | cmpa doesn't affect X 165 bne .L2 | loop until reached 166 #else 167 dbra %d1,.L2 | (NB- dbra doesn't affect X) 168 #endif 169 170 movl %d0,%d1 | fold 32 bit sum to 16 bits 171 swap %d1 | (NB- swap doesn't affect X) 172 #ifdef __mcoldfire__ 173 mvzw %d1,%d1 | zero extend %d1 (doesn't affect X) 174 mvzw %d0,%d0 | zero extend %d0 (doesn't affect X) 175 addxl %d1,%d0 | 176 jcc .L4 177 addql #1,%d0 178 #else 179 addxw %d1,%d0 180 jcc .L4 181 addw #1,%d0 182 #endif 183 .L4: 184 #ifdef __mcoldfire__ 185 mvzw %d0,%d0 186 #else 187 andl #0xffff,%d0 188 #endif 189 movl (%sp)+,%d2 190 rts 191 192 .L5: | deal with 1 or 3 excess bytes at the end of the buffer. 193 btst #1,%d1 194 jeq .L6 | if 1 excess 195 196 | 3 bytes excess 197 #ifdef __mcoldfire__ 198 mvzw (-3,%a0,%d1:l),%d2 | add in last full word then drop 199 #else 200 clrl %d2 201 movw (-3,%a0,%d1:l),%d2 | add in last full word then drop 202 #endif 203 addl %d2,%d0 | through to pick up last byte 204 205 .L6: | 1 byte excess 206 #ifdef __mcoldfire__ 207 mvzb (-1,%a0,%d1:l),%d2 208 #else 209 clrl %d2 210 movb (-1,%a0,%d1:l),%d2 211 #endif 212 lsll #8,%d2 213 addl %d2,%d0 214 jra .L1 215 216 .L7: | 2 bytes excess 217 #ifdef __mcoldfire__ 218 mvzw (-2,%a0,%d1:l),%d2 219 #else 220 clrl %d2 221 movw (-2,%a0,%d1:l),%d2 222 #endif 223 addl %d2,%d0 224 jra .L1 225
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