1 | /* |
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2 | * Checksum routine for Internet Protocol family headers. |
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3 | * |
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4 | * This routine is very heavily used in the network |
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5 | * code and should be modified for each CPU to be as fast as possible. |
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6 | * |
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7 | * This implementation is 386 version. |
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8 | * |
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9 | * $Id$ |
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10 | */ |
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11 | |
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12 | #include <stdio.h> /* for puts */ |
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13 | |
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14 | #undef ADDCARRY |
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15 | #define ADDCARRY(x) if ((x) > 0xffff) (x) -= 0xffff |
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16 | #define REDUCE {sum = (sum & 0xffff) + (sum >> 16); ADDCARRY(sum);} |
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17 | |
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18 | /* |
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19 | * Thanks to gcc we don't have to guess |
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20 | * which registers contain sum & w. |
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21 | */ |
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22 | #define ADD(n) __asm__ volatile \ |
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23 | ("addl " #n "(%2), %0" : "=r" (sum) : "0" (sum), "r" (w)) |
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24 | #define ADDC(n) __asm__ volatile \ |
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25 | ("adcl " #n "(%2), %0" : "=r" (sum) : "0" (sum), "r" (w)) |
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26 | #define LOAD(n) __asm__ volatile \ |
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27 | ("movb " #n "(%1), %0" : "=r" (junk) : "r" (w)) |
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28 | #define MOP __asm__ volatile \ |
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29 | ("adcl $0, %0" : "=r" (sum) : "0" (sum)) |
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30 | |
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31 | int |
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32 | in_cksum(m, len) |
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33 | register struct mbuf *m; |
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34 | register int len; |
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35 | { |
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36 | register u_short *w; |
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37 | register unsigned sum = 0; |
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38 | register int mlen = 0; |
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39 | int byte_swapped = 0; |
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40 | union { char c[2]; u_short s; } su; |
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41 | |
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42 | for (;m && len; m = m->m_next) { |
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43 | if (m->m_len == 0) |
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44 | continue; |
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45 | w = mtod(m, u_short *); |
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46 | if (mlen == -1) { |
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47 | /* |
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48 | * The first byte of this mbuf is the continuation |
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49 | * of a word spanning between this mbuf and the |
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50 | * last mbuf. |
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51 | */ |
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52 | |
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53 | /* su.c[0] is already saved when scanning previous |
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54 | * mbuf. sum was REDUCEd when we found mlen == -1 |
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55 | */ |
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56 | su.c[1] = *(u_char *)w; |
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57 | sum += su.s; |
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58 | w = (u_short *)((char *)w + 1); |
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59 | mlen = m->m_len - 1; |
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60 | len--; |
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61 | } else |
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62 | mlen = m->m_len; |
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63 | if (len < mlen) |
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64 | mlen = len; |
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65 | len -= mlen; |
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66 | /* |
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67 | * Force to long boundary so we do longword aligned |
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68 | * memory operations |
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69 | */ |
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70 | if (3 & (int) w) { |
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71 | REDUCE; |
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72 | if ((1 & (int) w) && (mlen > 0)) { |
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73 | sum <<= 8; |
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74 | su.c[0] = *(char *)w; |
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75 | w = (u_short *)((char *)w + 1); |
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76 | mlen--; |
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77 | byte_swapped = 1; |
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78 | } |
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79 | if ((2 & (int) w) && (mlen >= 2)) { |
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80 | sum += *w++; |
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81 | mlen -= 2; |
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82 | } |
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83 | } |
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84 | /* |
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85 | * Advance to a 486 cache line boundary. |
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86 | */ |
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87 | if (4 & (int) w && mlen >= 4) { |
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88 | ADD(0); |
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89 | MOP; |
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90 | w += 2; |
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91 | mlen -= 4; |
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92 | } |
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93 | if (8 & (int) w && mlen >= 8) { |
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94 | ADD(0); |
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95 | ADDC(4); |
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96 | MOP; |
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97 | w += 4; |
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98 | mlen -= 8; |
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99 | } |
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100 | /* |
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101 | * Do as much of the checksum as possible 32 bits at at time. |
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102 | * In fact, this loop is unrolled to make overhead from |
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103 | * branches &c small. |
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104 | */ |
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105 | mlen -= 1; |
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106 | while ((mlen -= 32) >= 0) { |
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107 | u_char junk; |
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108 | /* |
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109 | * Add with carry 16 words and fold in the last |
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110 | * carry by adding a 0 with carry. |
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111 | * |
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112 | * The early ADD(16) and the LOAD(32) are to load |
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113 | * the next 2 cache lines in advance on 486's. The |
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114 | * 486 has a penalty of 2 clock cycles for loading |
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115 | * a cache line, plus whatever time the external |
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116 | * memory takes to load the first word(s) addressed. |
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117 | * These penalties are unavoidable. Subsequent |
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118 | * accesses to a cache line being loaded (and to |
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119 | * other external memory?) are delayed until the |
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120 | * whole load finishes. These penalties are mostly |
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121 | * avoided by not accessing external memory for |
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122 | * 8 cycles after the ADD(16) and 12 cycles after |
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123 | * the LOAD(32). The loop terminates when mlen |
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124 | * is initially 33 (not 32) to guaranteed that |
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125 | * the LOAD(32) is within bounds. |
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126 | */ |
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127 | ADD(16); |
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128 | ADDC(0); |
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129 | ADDC(4); |
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130 | ADDC(8); |
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131 | ADDC(12); |
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132 | LOAD(32); |
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133 | ADDC(20); |
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134 | ADDC(24); |
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135 | ADDC(28); |
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136 | MOP; |
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137 | w += 16; |
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138 | } |
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139 | mlen += 32 + 1; |
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140 | if (mlen >= 32) { |
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141 | ADD(16); |
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142 | ADDC(0); |
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143 | ADDC(4); |
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144 | ADDC(8); |
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145 | ADDC(12); |
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146 | ADDC(20); |
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147 | ADDC(24); |
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148 | ADDC(28); |
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149 | MOP; |
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150 | w += 16; |
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151 | mlen -= 32; |
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152 | } |
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153 | if (mlen >= 16) { |
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154 | ADD(0); |
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155 | ADDC(4); |
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156 | ADDC(8); |
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157 | ADDC(12); |
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158 | MOP; |
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159 | w += 8; |
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160 | mlen -= 16; |
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161 | } |
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162 | if (mlen >= 8) { |
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163 | ADD(0); |
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164 | ADDC(4); |
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165 | MOP; |
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166 | w += 4; |
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167 | mlen -= 8; |
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168 | } |
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169 | if (mlen == 0 && byte_swapped == 0) |
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170 | continue; /* worth 1% maybe ?? */ |
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171 | REDUCE; |
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172 | while ((mlen -= 2) >= 0) { |
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173 | sum += *w++; |
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174 | } |
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175 | if (byte_swapped) { |
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176 | sum <<= 8; |
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177 | byte_swapped = 0; |
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178 | if (mlen == -1) { |
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179 | su.c[1] = *(char *)w; |
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180 | sum += su.s; |
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181 | mlen = 0; |
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182 | } else |
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183 | mlen = -1; |
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184 | } else if (mlen == -1) |
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185 | /* |
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186 | * This mbuf has odd number of bytes. |
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187 | * There could be a word split betwen |
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188 | * this mbuf and the next mbuf. |
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189 | * Save the last byte (to prepend to next mbuf). |
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190 | */ |
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191 | su.c[0] = *(char *)w; |
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192 | } |
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193 | |
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194 | if (len) |
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195 | puts("cksum: out of data"); |
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196 | if (mlen == -1) { |
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197 | /* The last mbuf has odd # of bytes. Follow the |
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198 | standard (the odd byte is shifted left by 8 bits) */ |
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199 | su.c[1] = 0; |
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200 | sum += su.s; |
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201 | } |
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202 | REDUCE; |
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203 | return (~sum & 0xffff); |
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204 | } |
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