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155 строки
7.1 KiB
C
155 строки
7.1 KiB
C
/*
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* Based on file found here:
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*
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* https://svnweb.freebsd.org/base/stable/10/sys/libkern/crc32.c?revision=256281
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*/
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/*-
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* COPYRIGHT (C) 1986 Gary S. Brown. You may use this program, or
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* code or tables extracted from it, as desired without restriction.
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*/
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/*
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* First, the polynomial itself and its table of feedback terms. The
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* polynomial is
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* X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
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*
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* Note that we take it "backwards" and put the highest-order term in
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* the lowest-order bit. The X^32 term is "implied"; the LSB is the
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* X^31 term, etc. The X^0 term (usually shown as "+1") results in
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* the MSB being 1
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*
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* Note that the usual hardware shift register implementation, which
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* is what we're using (we're merely optimizing it by doing eight-bit
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* chunks at a time) shifts bits into the lowest-order term. In our
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* implementation, that means shifting towards the right. Why do we
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* do it this way? Because the calculated CRC must be transmitted in
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* order from highest-order term to lowest-order term. UARTs transmit
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* characters in order from LSB to MSB. By storing the CRC this way
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* we hand it to the UART in the order low-byte to high-byte; the UART
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* sends each low-bit to hight-bit; and the result is transmission bit
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* by bit from highest- to lowest-order term without requiring any bit
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* shuffling on our part. Reception works similarly
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*
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* The feedback terms table consists of 256, 32-bit entries. Notes
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*
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* The table can be generated at runtime if desired; code to do so
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* is shown later. It might not be obvious, but the feedback
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* terms simply represent the results of eight shift/xor opera
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* tions for all combinations of data and CRC register values
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*
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* The values must be right-shifted by eight bits by the "updcrc
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* logic; the shift must be unsigned (bring in zeroes). On some
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* hardware you could probably optimize the shift in assembler by
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* using byte-swap instructions
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* polynomial $edb88320
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*
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*
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* CRC32 code derived from work by Gary S. Brown.
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*/
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#include "crc32c.h"
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/* CRC32C routines, these use a different polynomial */
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/*****************************************************************/
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/* */
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/* CRC LOOKUP TABLE */
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/* ================ */
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/* The following CRC lookup table was generated automagically */
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/* by the Rocksoft^tm Model CRC Algorithm Table Generation */
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/* Program V1.0 using the following model parameters: */
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/* */
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/* Width : 4 bytes. */
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/* Poly : 0x1EDC6F41L */
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/* Reverse : TRUE. */
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/* */
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/* For more information on the Rocksoft^tm Model CRC Algorithm, */
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/* see the document titled "A Painless Guide to CRC Error */
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/* Detection Algorithms" by Ross Williams */
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/* (ross@guest.adelaide.edu.au.). This document is likely to be */
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/* in the FTP archive "ftp.adelaide.edu.au/pub/rocksoft". */
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/* */
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/*****************************************************************/
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static const uint32_t crc32Table[256] = {
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0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
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0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
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0x8AD958CFL, 0x78B2DBCCL, 0x6BE22838L, 0x9989AB3BL,
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0x4D43CFD0L, 0xBF284CD3L, 0xAC78BF27L, 0x5E133C24L,
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0x105EC76FL, 0xE235446CL, 0xF165B798L, 0x030E349BL,
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0xD7C45070L, 0x25AFD373L, 0x36FF2087L, 0xC494A384L,
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0x9A879FA0L, 0x68EC1CA3L, 0x7BBCEF57L, 0x89D76C54L,
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0x5D1D08BFL, 0xAF768BBCL, 0xBC267848L, 0x4E4DFB4BL,
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0x20BD8EDEL, 0xD2D60DDDL, 0xC186FE29L, 0x33ED7D2AL,
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0xE72719C1L, 0x154C9AC2L, 0x061C6936L, 0xF477EA35L,
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0xAA64D611L, 0x580F5512L, 0x4B5FA6E6L, 0xB93425E5L,
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0x6DFE410EL, 0x9F95C20DL, 0x8CC531F9L, 0x7EAEB2FAL,
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0x30E349B1L, 0xC288CAB2L, 0xD1D83946L, 0x23B3BA45L,
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0xF779DEAEL, 0x05125DADL, 0x1642AE59L, 0xE4292D5AL,
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0xBA3A117EL, 0x4851927DL, 0x5B016189L, 0xA96AE28AL,
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0x7DA08661L, 0x8FCB0562L, 0x9C9BF696L, 0x6EF07595L,
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0x417B1DBCL, 0xB3109EBFL, 0xA0406D4BL, 0x522BEE48L,
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0x86E18AA3L, 0x748A09A0L, 0x67DAFA54L, 0x95B17957L,
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0xCBA24573L, 0x39C9C670L, 0x2A993584L, 0xD8F2B687L,
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0x0C38D26CL, 0xFE53516FL, 0xED03A29BL, 0x1F682198L,
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0x5125DAD3L, 0xA34E59D0L, 0xB01EAA24L, 0x42752927L,
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0x96BF4DCCL, 0x64D4CECFL, 0x77843D3BL, 0x85EFBE38L,
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0xDBFC821CL, 0x2997011FL, 0x3AC7F2EBL, 0xC8AC71E8L,
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0x1C661503L, 0xEE0D9600L, 0xFD5D65F4L, 0x0F36E6F7L,
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0x61C69362L, 0x93AD1061L, 0x80FDE395L, 0x72966096L,
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0xA65C047DL, 0x5437877EL, 0x4767748AL, 0xB50CF789L,
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0xEB1FCBADL, 0x197448AEL, 0x0A24BB5AL, 0xF84F3859L,
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0x2C855CB2L, 0xDEEEDFB1L, 0xCDBE2C45L, 0x3FD5AF46L,
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0x7198540DL, 0x83F3D70EL, 0x90A324FAL, 0x62C8A7F9L,
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0xB602C312L, 0x44694011L, 0x5739B3E5L, 0xA55230E6L,
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0xFB410CC2L, 0x092A8FC1L, 0x1A7A7C35L, 0xE811FF36L,
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0x3CDB9BDDL, 0xCEB018DEL, 0xDDE0EB2AL, 0x2F8B6829L,
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0x82F63B78L, 0x709DB87BL, 0x63CD4B8FL, 0x91A6C88CL,
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0x456CAC67L, 0xB7072F64L, 0xA457DC90L, 0x563C5F93L,
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0x082F63B7L, 0xFA44E0B4L, 0xE9141340L, 0x1B7F9043L,
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0xCFB5F4A8L, 0x3DDE77ABL, 0x2E8E845FL, 0xDCE5075CL,
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0x92A8FC17L, 0x60C37F14L, 0x73938CE0L, 0x81F80FE3L,
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0x55326B08L, 0xA759E80BL, 0xB4091BFFL, 0x466298FCL,
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0x1871A4D8L, 0xEA1A27DBL, 0xF94AD42FL, 0x0B21572CL,
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0xDFEB33C7L, 0x2D80B0C4L, 0x3ED04330L, 0xCCBBC033L,
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0xA24BB5A6L, 0x502036A5L, 0x4370C551L, 0xB11B4652L,
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0x65D122B9L, 0x97BAA1BAL, 0x84EA524EL, 0x7681D14DL,
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0x2892ED69L, 0xDAF96E6AL, 0xC9A99D9EL, 0x3BC21E9DL,
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0xEF087A76L, 0x1D63F975L, 0x0E330A81L, 0xFC588982L,
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0xB21572C9L, 0x407EF1CAL, 0x532E023EL, 0xA145813DL,
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0x758FE5D6L, 0x87E466D5L, 0x94B49521L, 0x66DF1622L,
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0x38CC2A06L, 0xCAA7A905L, 0xD9F75AF1L, 0x2B9CD9F2L,
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0xFF56BD19L, 0x0D3D3E1AL, 0x1E6DCDEEL, 0xEC064EEDL,
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0xC38D26C4L, 0x31E6A5C7L, 0x22B65633L, 0xD0DDD530L,
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0x0417B1DBL, 0xF67C32D8L, 0xE52CC12CL, 0x1747422FL,
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0x49547E0BL, 0xBB3FFD08L, 0xA86F0EFCL, 0x5A048DFFL,
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0x8ECEE914L, 0x7CA56A17L, 0x6FF599E3L, 0x9D9E1AE0L,
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0xD3D3E1ABL, 0x21B862A8L, 0x32E8915CL, 0xC083125FL,
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0x144976B4L, 0xE622F5B7L, 0xF5720643L, 0x07198540L,
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0x590AB964L, 0xAB613A67L, 0xB831C993L, 0x4A5A4A90L,
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0x9E902E7BL, 0x6CFBAD78L, 0x7FAB5E8CL, 0x8DC0DD8FL,
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0xE330A81AL, 0x115B2B19L, 0x020BD8EDL, 0xF0605BEEL,
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0x24AA3F05L, 0xD6C1BC06L, 0xC5914FF2L, 0x37FACCF1L,
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0x69E9F0D5L, 0x9B8273D6L, 0x88D28022L, 0x7AB90321L,
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0xAE7367CAL, 0x5C18E4C9L, 0x4F48173DL, 0xBD23943EL,
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0xF36E6F75L, 0x0105EC76L, 0x12551F82L, 0xE03E9C81L,
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0x34F4F86AL, 0xC69F7B69L, 0xD5CF889DL, 0x27A40B9EL,
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0x79B737BAL, 0x8BDCB4B9L, 0x988C474DL, 0x6AE7C44EL,
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0xBE2DA0A5L, 0x4C4623A6L, 0x5F16D052L, 0xAD7D5351L
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};
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// NOTE: See source URL at top of this file for multitable implementation which
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// offers a performance boost at the cost of ~8KB of static tables.
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uint32_t
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ComputeCrc32c(uint32_t crc, const void *buf, size_t size)
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{
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const uint8_t *p = buf;
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while (size--)
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crc = crc32Table[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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return crc;
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}
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