Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/i386/i386/in_cksum_machdep.c
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1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 1990 The Regents of the University of California. 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of the University nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 * 31 * from tahoe: in_cksum.c 1.2 86/01/05 32 * from: @(#)in_cksum.c 1.3 (Berkeley) 1/19/91 33 */ 34 35 #include <sys/cdefs.h> 36 __FBSDID("$FreeBSD$"); 37 38 #include <sys/param.h> 39 #include <sys/systm.h> 40 #include <sys/mbuf.h> 41 42 #include <netinet/in.h> 43 #include <netinet/in_systm.h> 44 #include <netinet/ip.h> 45 46 #include <machine/in_cksum.h> 47 48 /* 49 * Checksum routine for Internet Protocol family headers. 50 * 51 * This routine is very heavily used in the network 52 * code and should be modified for each CPU to be as fast as possible. 53 * 54 * This implementation is 386 version. 55 */ 56 57 #undef ADDCARRY 58 #define ADDCARRY(x) if ((x) > 0xffff) (x) -= 0xffff 59 #define REDUCE {sum = (sum & 0xffff) + (sum >> 16); ADDCARRY(sum);} 60 61 /* 62 * These asm statements require __volatile because they pass information 63 * via the condition codes. GCC does not currently provide a way to specify 64 * the condition codes as an input or output operand. 65 * 66 * The LOAD macro below is effectively a prefetch into cache. GCC will 67 * load the value into a register but will not use it. Since modern CPUs 68 * reorder operations, this will generally take place in parallel with 69 * other calculations. 70 */ 71 u_short 72 in_cksum_skip(m, len, skip) 73 struct mbuf *m; 74 int len; 75 int skip; 76 { 77 u_short *w; 78 unsigned sum = 0; 79 int mlen = 0; 80 int byte_swapped = 0; 81 union { char c[2]; u_short s; } su; 82 83 len -= skip; 84 for (; skip && m; m = m->m_next) { 85 if (m->m_len > skip) { 86 mlen = m->m_len - skip; 87 w = (u_short *)(mtod(m, u_char *) + skip); 88 goto skip_start; 89 } else { 90 skip -= m->m_len; 91 } 92 } 93 94 for (;m && len; m = m->m_next) { 95 if (m->m_len == 0) 96 continue; 97 w = mtod(m, u_short *); 98 if (mlen == -1) { 99 /* 100 * The first byte of this mbuf is the continuation 101 * of a word spanning between this mbuf and the 102 * last mbuf. 103 */ 104 105 /* su.c[0] is already saved when scanning previous 106 * mbuf. sum was REDUCEd when we found mlen == -1 107 */ 108 su.c[1] = *(u_char *)w; 109 sum += su.s; 110 w = (u_short *)((char *)w + 1); 111 mlen = m->m_len - 1; 112 len--; 113 } else 114 mlen = m->m_len; 115 skip_start: 116 if (len < mlen) 117 mlen = len; 118 len -= mlen; 119 /* 120 * Force to long boundary so we do longword aligned 121 * memory operations 122 */ 123 if (3 & (int) w) { 124 REDUCE; 125 if ((1 & (int) w) && (mlen > 0)) { 126 sum <<= 8; 127 su.c[0] = *(char *)w; 128 w = (u_short *)((char *)w + 1); 129 mlen--; 130 byte_swapped = 1; 131 } 132 if ((2 & (int) w) && (mlen >= 2)) { 133 sum += *w++; 134 mlen -= 2; 135 } 136 } 137 /* 138 * Advance to a 486 cache line boundary. 139 */ 140 if (4 & (int) w && mlen >= 4) { 141 __asm __volatile ( 142 "addl %1, %0\n" 143 "adcl $0, %0" 144 : "+r" (sum) 145 : "g" (((const u_int32_t *)w)[0]) 146 ); 147 w += 2; 148 mlen -= 4; 149 } 150 if (8 & (int) w && mlen >= 8) { 151 __asm __volatile ( 152 "addl %1, %0\n" 153 "adcl %2, %0\n" 154 "adcl $0, %0" 155 : "+r" (sum) 156 : "g" (((const u_int32_t *)w)[0]), 157 "g" (((const u_int32_t *)w)[1]) 158 ); 159 w += 4; 160 mlen -= 8; 161 } 162 /* 163 * Do as much of the checksum as possible 32 bits at at time. 164 * In fact, this loop is unrolled to make overhead from 165 * branches &c small. 166 */ 167 mlen -= 1; 168 while ((mlen -= 32) >= 0) { 169 /* 170 * Add with carry 16 words and fold in the last 171 * carry by adding a 0 with carry. 172 * 173 * The early ADD(16) and the LOAD(32) are to load 174 * the next 2 cache lines in advance on 486's. The 175 * 486 has a penalty of 2 clock cycles for loading 176 * a cache line, plus whatever time the external 177 * memory takes to load the first word(s) addressed. 178 * These penalties are unavoidable. Subsequent 179 * accesses to a cache line being loaded (and to 180 * other external memory?) are delayed until the 181 * whole load finishes. These penalties are mostly 182 * avoided by not accessing external memory for 183 * 8 cycles after the ADD(16) and 12 cycles after 184 * the LOAD(32). The loop terminates when mlen 185 * is initially 33 (not 32) to guaranteed that 186 * the LOAD(32) is within bounds. 187 */ 188 __asm __volatile ( 189 "addl %1, %0\n" 190 "adcl %2, %0\n" 191 "adcl %3, %0\n" 192 "adcl %4, %0\n" 193 "adcl %5, %0\n" 194 "mov %6, %%eax\n" 195 "adcl %7, %0\n" 196 "adcl %8, %0\n" 197 "adcl %9, %0\n" 198 "adcl $0, %0" 199 : "+r" (sum) 200 : "g" (((const u_int32_t *)w)[4]), 201 "g" (((const u_int32_t *)w)[0]), 202 "g" (((const u_int32_t *)w)[1]), 203 "g" (((const u_int32_t *)w)[2]), 204 "g" (((const u_int32_t *)w)[3]), 205 "g" (((const u_int32_t *)w)[8]), 206 "g" (((const u_int32_t *)w)[5]), 207 "g" (((const u_int32_t *)w)[6]), 208 "g" (((const u_int32_t *)w)[7]) 209 : "eax" 210 ); 211 w += 16; 212 } 213 mlen += 32 + 1; 214 if (mlen >= 32) { 215 __asm __volatile ( 216 "addl %1, %0\n" 217 "adcl %2, %0\n" 218 "adcl %3, %0\n" 219 "adcl %4, %0\n" 220 "adcl %5, %0\n" 221 "adcl %6, %0\n" 222 "adcl %7, %0\n" 223 "adcl %8, %0\n" 224 "adcl $0, %0" 225 : "+r" (sum) 226 : "g" (((const u_int32_t *)w)[4]), 227 "g" (((const u_int32_t *)w)[0]), 228 "g" (((const u_int32_t *)w)[1]), 229 "g" (((const u_int32_t *)w)[2]), 230 "g" (((const u_int32_t *)w)[3]), 231 "g" (((const u_int32_t *)w)[5]), 232 "g" (((const u_int32_t *)w)[6]), 233 "g" (((const u_int32_t *)w)[7]) 234 ); 235 w += 16; 236 mlen -= 32; 237 } 238 if (mlen >= 16) { 239 __asm __volatile ( 240 "addl %1, %0\n" 241 "adcl %2, %0\n" 242 "adcl %3, %0\n" 243 "adcl %4, %0\n" 244 "adcl $0, %0" 245 : "+r" (sum) 246 : "g" (((const u_int32_t *)w)[0]), 247 "g" (((const u_int32_t *)w)[1]), 248 "g" (((const u_int32_t *)w)[2]), 249 "g" (((const u_int32_t *)w)[3]) 250 ); 251 w += 8; 252 mlen -= 16; 253 } 254 if (mlen >= 8) { 255 __asm __volatile ( 256 "addl %1, %0\n" 257 "adcl %2, %0\n" 258 "adcl $0, %0" 259 : "+r" (sum) 260 : "g" (((const u_int32_t *)w)[0]), 261 "g" (((const u_int32_t *)w)[1]) 262 ); 263 w += 4; 264 mlen -= 8; 265 } 266 if (mlen == 0 && byte_swapped == 0) 267 continue; /* worth 1% maybe ?? */ 268 REDUCE; 269 while ((mlen -= 2) >= 0) { 270 sum += *w++; 271 } 272 if (byte_swapped) { 273 sum <<= 8; 274 byte_swapped = 0; 275 if (mlen == -1) { 276 su.c[1] = *(char *)w; 277 sum += su.s; 278 mlen = 0; 279 } else 280 mlen = -1; 281 } else if (mlen == -1) 282 /* 283 * This mbuf has odd number of bytes. 284 * There could be a word split between 285 * this mbuf and the next mbuf. 286 * Save the last byte (to prepend to next mbuf). 287 */ 288 su.c[0] = *(char *)w; 289 } 290 291 if (len) 292 printf("%s: out of data by %d\n", __func__, len); 293 if (mlen == -1) { 294 /* The last mbuf has odd # of bytes. Follow the 295 standard (the odd byte is shifted left by 8 bits) */ 296 su.c[1] = 0; 297 sum += su.s; 298 } 299 REDUCE; 300 return (~sum & 0xffff); 301 }
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