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   1 ;
   2 ; crc32.s
   3 ;
   4 ; 32-bit CRC calculation
   5 ;
   6 ;  © 1993-1998 Straylight
   7 ;
   8
   9 ;----- Licensing note -------------------------------------------------------
  10 ;
  11 ; This file is part of Straylight's Steel library.
  12 ;
  13 ; Steel is free software; you can redistribute it and/or modify
  14 ; it under the terms of the GNU General Public License as published by
  15 ; the Free Software Foundation; either version 2, or (at your option)
  16 ; any later version.
  17 ;
  18 ; Steel is distributed in the hope that it will be useful,
  19 ; but WITHOUT ANY WARRANTY; without even the implied warranty of
  20 ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  21 ; GNU General Public License for more details.
  22 ;
  23 ; You should have received a copy of the GNU General Public License
  24 ; along with Steel.  If not, write to the Free Software Foundation,
  25 ; 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  26
  27                 GET     libs:header
  28                 GET     libs:swis
  29
  30                 AREA    |C$$Code|,CODE,READONLY
  31
  32 ;----- crc32 ----------------------------------------------------------------
  33 ;
  34 ; Calculates 32-bit Cyclic Redundancy Check values for a given chunk of
  35 ; data.  A calculation may be performed in stages.
  36 ;
  37 ; The method used is the PKZip/Ethernet algorithm.  For reference, the
  38 ; parameters to the Rocksoft^tm Model CRC Algorithm are:
  39 ;
  40 ; Name   : Straylight Cyclic Redundancy Check algorithm
  41 ; Width  : 32
  42 ; Poly   : 04C11DB7
  43 ; Init   : FFFFFFFF
  44 ; RefIn  : True
  45 ; RefOut : True
  46 ; XorOut : FFFFFFFF
  47 ; Check  : CBF43926
  48 ;
  49 ; The routine is very small (and hopefully pretty quick, too).  The table
  50 ; is rather large, though.
  51 ;
  52 ; The code can be called from any APCS-conformant langauge.  The C prototype
  53 ; is
  54 ;
  55 ;       long crc32(     long seed,      /* R0==seed value (0 to start)  */
  56 ;                       void *data,     /* R1==pointer to data to check */
  57 ;                       size_t size,    /* R2==length of data           */
  58 ;                       int diff);      /* R3==diff between check bytes */
  59 ;
  60 ; In normal use, the seed is 0 for the first call, and the previoud returned
  61 ; value for subsequent calculations.
  62 ;
  63 ; The 'diff' value gives the difference in address between bytes to check,
  64 ; so diff==1 means check all bytes, diff==2 means check every other byte,
  65 ; and so on.
  66 ;
  67
  68                 EXPORT  crc32
  69 crc32           ROUT
  70
  71                 STMFD   R13!,{R1-R4,R14}
  72                 MVN     R0,R0                   ;R0 = R0 XOR &FFFFFFFF!
  73                 ADR     R4,crctable             ;Point to my magic table
  74
  75 00              LDRB    R14,[R1],R3             ;Get byte from stream
  76                 EOR     R14,R14,R0              ;XOR register with byte
  77                 AND     R14,R14,#&FF            ;Multiply to word, and mask
  78                 LDR     R14,[R4,R14,LSL #2]     ;Get word from table
  79                 EOR     R0,R14,R0,LSR #8        ;EOR with shifted register
  80                 SUBS    R2,R2,R3                ;Decrement counter
  81                 BGT     %b00                    ;If necessary, branch back
  82                 MVN     R0,R0                   ;R0 = R0 XOR &FFFFFFFF again
  83                 LDMFD   R13!,{R1-R4,PC}^
  84
  85                 LTORG
  86
  87 ;----- The magic table ------------------------------------------------------
  88 ;
  89 ; The numbers in this table were generated using the Rocksoft^tm Model CRC
  90 ; Algorithm Table Generation Table Program V1.0, written by Ross Williams.
  91 ; Our thanks to him for placing this program in the public domain.
  92 ;
  93
  94 crctable        DCD     &00000000,&77073096,&EE0E612C,&990951BA
  95                 DCD     &076DC419,&706AF48F,&E963A535,&9E6495A3
  96                 DCD     &0EDB8832,&79DCB8A4,&E0D5E91E,&97D2D988
  97                 DCD     &09B64C2B,&7EB17CBD,&E7B82D07,&90BF1D91
  98                 DCD     &1DB71064,&6AB020F2,&F3B97148,&84BE41DE
  99                 DCD     &1ADAD47D,&6DDDE4EB,&F4D4B551,&83D385C7
 100                 DCD     &136C9856,&646BA8C0,&FD62F97A,&8A65C9EC
 101                 DCD     &14015C4F,&63066CD9,&FA0F3D63,&8D080DF5
 102
 103                 DCD     &3B6E20C8,&4C69105E,&D56041E4,&A2677172
 104                 DCD     &3C03E4D1,&4B04D447,&D20D85FD,&A50AB56B
 105                 DCD     &35B5A8FA,&42B2986C,&DBBBC9D6,&ACBCF940
 106                 DCD     &32D86CE3,&45DF5C75,&DCD60DCF,&ABD13D59
 107                 DCD     &26D930AC,&51DE003A,&C8D75180,&BFD06116
 108                 DCD     &21B4F4B5,&56B3C423,&CFBA9599,&B8BDA50F
 109                 DCD     &2802B89E,&5F058808,&C60CD9B2,&B10BE924
 110                 DCD     &2F6F7C87,&58684C11,&C1611DAB,&B6662D3D
 111
 112                 DCD     &76DC4190,&01DB7106,&98D220BC,&EFD5102A
 113                 DCD     &71B18589,&06B6B51F,&9FBFE4A5,&E8B8D433
 114                 DCD     &7807C9A2,&0F00F934,&9609A88E,&E10E9818
 115                 DCD     &7F6A0DBB,&086D3D2D,&91646C97,&E6635C01
 116                 DCD     &6B6B51F4,&1C6C6162,&856530D8,&F262004E
 117                 DCD     &6C0695ED,&1B01A57B,&8208F4C1,&F50FC457
 118                 DCD     &65B0D9C6,&12B7E950,&8BBEB8EA,&FCB9887C
 119                 DCD     &62DD1DDF,&15DA2D49,&8CD37CF3,&FBD44C65
 120
 121                 DCD     &4DB26158,&3AB551CE,&A3BC0074,&D4BB30E2
 122                 DCD     &4ADFA541,&3DD895D7,&A4D1C46D,&D3D6F4FB
 123                 DCD     &4369E96A,&346ED9FC,&AD678846,&DA60B8D0
 124                 DCD     &44042D73,&33031DE5,&AA0A4C5F,&DD0D7CC9
 125                 DCD     &5005713C,&270241AA,&BE0B1010,&C90C2086
 126                 DCD     &5768B525,&206F85B3,&B966D409,&CE61E49F
 127                 DCD     &5EDEF90E,&29D9C998,&B0D09822,&C7D7A8B4
 128                 DCD     &59B33D17,&2EB40D81,&B7BD5C3B,&C0BA6CAD
 129
 130                 DCD     &EDB88320,&9ABFB3B6,&03B6E20C,&74B1D29A
 131                 DCD     &EAD54739,&9DD277AF,&04DB2615,&73DC1683
 132                 DCD     &E3630B12,&94643B84,&0D6D6A3E,&7A6A5AA8
 133                 DCD     &E40ECF0B,&9309FF9D,&0A00AE27,&7D079EB1
 134                 DCD     &F00F9344,&8708A3D2,&1E01F268,&6906C2FE
 135                 DCD     &F762575D,&806567CB,&196C3671,&6E6B06E7
 136                 DCD     &FED41B76,&89D32BE0,&10DA7A5A,&67DD4ACC
 137                 DCD     &F9B9DF6F,&8EBEEFF9,&17B7BE43,&60B08ED5
 138
 139                 DCD     &D6D6A3E8,&A1D1937E,&38D8C2C4,&4FDFF252
 140                 DCD     &D1BB67F1,&A6BC5767,&3FB506DD,&48B2364B
 141                 DCD     &D80D2BDA,&AF0A1B4C,&36034AF6,&41047A60
 142                 DCD     &DF60EFC3,&A867DF55,&316E8EEF,&4669BE79
 143                 DCD     &CB61B38C,&BC66831A,&256FD2A0,&5268E236
 144                 DCD     &CC0C7795,&BB0B4703,&220216B9,&5505262F
 145                 DCD     &C5BA3BBE,&B2BD0B28,&2BB45A92,&5CB36A04
 146                 DCD     &C2D7FFA7,&B5D0CF31,&2CD99E8B,&5BDEAE1D
 147
 148                 DCD     &9B64C2B0,&EC63F226,&756AA39C,&026D930A
 149                 DCD     &9C0906A9,&EB0E363F,&72076785,&05005713
 150                 DCD     &95BF4A82,&E2B87A14,&7BB12BAE,&0CB61B38
 151                 DCD     &92D28E9B,&E5D5BE0D,&7CDCEFB7,&0BDBDF21
 152                 DCD     &86D3D2D4,&F1D4E242,&68DDB3F8,&1FDA836E
 153                 DCD     &81BE16CD,&F6B9265B,&6FB077E1,&18B74777
 154                 DCD     &88085AE6,&FF0F6A70,&66063BCA,&11010B5C
 155                 DCD     &8F659EFF,&F862AE69,&616BFFD3,&166CCF45
 156
 157                 DCD     &A00AE278,&D70DD2EE,&4E048354,&3903B3C2
 158                 DCD     &A7672661,&D06016F7,&4969474D,&3E6E77DB
 159                 DCD     &AED16A4A,&D9D65ADC,&40DF0B66,&37D83BF0
 160                 DCD     &A9BCAE53,&DEBB9EC5,&47B2CF7F,&30B5FFE9
 161                 DCD     &BDBDF21C,&CABAC28A,&53B39330,&24B4A3A6
 162                 DCD     &BAD03605,&CDD70693,&54DE5729,&23D967BF
 163                 DCD     &B3667A2E,&C4614AB8,&5D681B02,&2A6F2B94
 164                 DCD     &B40BBE37,&C30C8EA1,&5A05DF1B,&2D02EF8D
 165
 166                 END