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1 Enclosed is compress version 3.0 with the following changes:
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2
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3 1. "Block" compression is performed. After the BITS run out, the
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4 compression ratio is checked every so often. If it is decreasing,
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5 the table is cleared and a new set of substrings are generated.
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6
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7 This makes the output of compress 3.0 not compatable with that of
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8 compress 2.0. However, compress 3.0 still accepts the output of
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9 compress 2.0. To generate output that is compatable with compress
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10 2.0, use the undocumented "-C" flag.
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11
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12 2. A quiet "-q" flag has been added for use by the news system.
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13
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14 3. The character chaining has been deleted and the program now uses
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15 hashing. This improves the speed of the program, especially
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16 during decompression. Other speed improvements have been made,
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17 such as using putc() instead of fwrite().
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18
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19 4. A large table is used on large machines when a relatively small
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20 number of bits is specified. This saves much time when compressing
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21 for a 16-bit machine on a 32-bit virtual machine. Note that the
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22 speed improvement only occurs when the input file is > 30000
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23 characters, and the -b BITS is less than or equal to the cutoff
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24 described below.
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25
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26 Most of these changes were made by James A. Woods (ames!jaw). Thank you
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27 James!
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28
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29 Version 3.0 has been beta tested on many machines.
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30
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31 To compile compress:
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32
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33 cc -O -DUSERMEM=usermem -o compress compress.c
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34
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35 Where "usermem" is the amount of physical user memory available (in bytes).
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36 If any physical memory is to be reserved for other processes, put in
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37 "-DSACREDMEM sacredmem", where "sacredmem" is the amount to be reserved.
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38
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39 The difference "usermem-sacredmem" determines the maximum BITS that can be
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40 specified, and the cutoff bits where the large+fast table is used.
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41
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42 memory: at least BITS cutoff
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43 ------ -- ----- ---- ------
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44 4,718,592 16 13
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45 2,621,440 16 12
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46 1,572,864 16 11
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47 1,048,576 16 10
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48 631,808 16 --
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49 329,728 15 --
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50 178,176 14 --
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51 99,328 13 --
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52 0 12 --
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53
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54 The default memory size is 750,000 which gives a maximum BITS=16 and no
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55 large+fast table.
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56
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57 The maximum bits can be overrulled by specifying "-DBITS=bits" at
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58 compilation time.
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59
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60 If your machine doesn't support unsigned characters, define "NO_UCHAR"
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61 when compiling.
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62
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63 If your machine has "int" as 16-bits, define "SHORT_INT" when compiling.
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64
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65 After compilation, move "compress" to a standard executable location, such
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66 as /usr/local. Then:
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67 cd /usr/local
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68 ln compress uncompress
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69 ln compress zcat
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70
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71 On machines that have a fixed stack size (such as Perkin-Elmer), set the
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72 stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer).
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73
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74 Next, install the manual (compress.l).
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75 cp compress.l /usr/man/manl
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76 cd /usr/man/manl
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77 ln compress.l uncompress.l
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78 ln compress.l zcat.l
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79
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80 - or -
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81
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82 cp compress.l /usr/man/man1/compress.1
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83 cd /usr/man/man1
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84 ln compress.1 uncompress.1
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85 ln compress.1 zcat.1
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86
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87 The zmore shell script and manual page are for use on systems that have a
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88 "more(1)" program. Install the shell script and the manual page in a "bin"
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89 and "man" directory, respectively. If your system doesn't have the
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90 "more(1)" program, just skip "zmore".
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91
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92 regards,
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93 petsd!joe
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94
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95 Here is the README file from the previous version of compress (2.0):
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96
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97 >Enclosed is compress.c version 2.0 with the following bugs fixed:
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98 >
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99 >1. The packed files produced by compress are different on different
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100 > machines and dependent on the vax sysgen option.
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101 > The bug was in the different byte/bit ordering on the
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102 > various machines. This has been fixed.
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103 >
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104 > This version is NOT compatible with the original vax posting
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105 > unless the '-DCOMPATIBLE' option is specified to the C
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106 > compiler. The original posting has a bug which I fixed,
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107 > causing incompatible files. I recommend you NOT to use this
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108 > option unless you already have a lot of packed files from
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109 > the original posting by thomas.
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110 >2. The exit status is not well defined (on some machines) causing the
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111 > scripts to fail.
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112 > The exit status is now 0,1 or 2 and is documented in
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113 > compress.l.
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114 >3. The function getopt() is not available in all C libraries.
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115 > The function getopt() is no longer referenced by the
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116 > program.
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117 >4. Error status is not being checked on the fwrite() and fflush() calls.
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118 > Fixed.
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119 >
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120 >The following enhancements have been made:
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121 >
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122 >1. Added facilities of "compact" into the compress program. "Pack",
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123 > "Unpack", and "Pcat" are no longer required (no longer supplied).
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124 >2. Installed work around for C compiler bug with "-O".
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125 >3. Added a magic number header (\037\235). Put the bits specified
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126 > in the file.
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127 >4. Added "-f" flag to force overwrite of output file.
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128 >5. Added "-c" flag and "zcat" program. 'ln compress zcat' after you
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129 > compile.
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130 >6. The 'uncompress' script has been deleted; simply
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131 > 'ln compress uncompress' after you compile and it will work.
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132 >7. Removed extra bit masking for machines that support unsigned
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133 > characters. If your machine doesn't support unsigned characters,
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134 > define "NO_UCHAR" when compiling.
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135 >
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136 >Compile "compress.c" with "-O -o compress" flags. Move "compress" to a
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137 >standard executable location, such as /usr/local. Then:
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138 > cd /usr/local
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139 > ln compress uncompress
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140 > ln compress zcat
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141 >
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142 >On machines that have a fixed stack size (such as Perkin-Elmer), set the
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143 >stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer).
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144 >
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145 >Next, install the manual (compress.l).
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146 > cp compress.l /usr/man/manl - or -
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147 > cp compress.l /usr/man/man1/compress.1
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148 >
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149 >Here is the README that I sent with my first posting:
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150 >
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151 >>Enclosed is a modified version of compress.c, along with scripts to make it
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152 >>run identically to pack(1), unpack(1), an pcat(1). Here is what I
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153 >>(petsd!joe) and a colleague (petsd!peora!srd) did:
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154 >>
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155 >>1. Removed VAX dependencies.
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156 >>2. Changed the struct to separate arrays; saves mucho memory.
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157 >>3. Did comparisons in unsigned, where possible. (Faster on Perkin-Elmer.)
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158 >>4. Sorted the character next chain and changed the search to stop
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159 >>prematurely. This saves a lot on the execution time when compressing.
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160 >>
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161 >>This version is totally compatible with the original version. Even though
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162 >>lint(1) -p has no complaints about compress.c, it won't run on a 16-bit
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163 >>machine, due to the size of the arrays.
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164 >>
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165 >>Here is the README file from the original author:
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166 >>
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167 >>>Well, with all this discussion about file compression (for news batching
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168 >>>in particular) going around, I decided to implement the text compression
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169 >>>algorithm described in the June Computer magazine. The author claimed
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170 >>>blinding speed and good compression ratios. It's certainly faster than
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171 >>>compact (but, then, what wouldn't be), but it's also the same speed as
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172 >>>pack, and gets better compression than both of them. On 350K bytes of
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173 >>>unix-wizards, compact took about 8 minutes of CPU, pack took about 80
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174 >>>seconds, and compress (herein) also took 80 seconds. But, compact and
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175 >>>pack got about 30% compression, whereas compress got over 50%. So, I
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176 >>>decided I had something, and that others might be interested, too.
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177 >>>
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178 >>>As is probably true of compact and pack (although I haven't checked),
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179 >>>the byte order within a word is probably relevant here, but as long as
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180 >>>you stay on a single machine type, you should be ok. (Can anybody
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181 >>>elucidate on this?) There are a couple of asm's in the code (extv and
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182 >>>insv instructions), so anyone porting it to another machine will have to
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183 >>>deal with this anyway (and could probably make it compatible with Vax
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184 >>>byte order at the same time). Anyway, I've linted the code (both with
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185 >>>and without -p), so it should run elsewhere. Note the longs in the
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186 >>>code, you can take these out if you reduce BITS to <= 15.
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187 >>>
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188 >>>Have fun, and as always, if you make good enhancements, or bug fixes,
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189 >>>I'd like to see them.
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190 >>>
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191 >>>=Spencer (thomas@utah-20, {harpo,hplabs,arizona}!utah-cs!thomas)
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192 >>
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193 >> regards,
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194 >> joe
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195 >>
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196 >>--
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197 >>Full-Name: Joseph M. Orost
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198 >>UUCP: ..!{decvax,ucbvax,ihnp4}!vax135!petsd!joe
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199 >>US Mail: MS 313; Perkin-Elmer; 106 Apple St; Tinton Falls, NJ 07724
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200 >>Phone: (201) 870-5844
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