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<title>crc32</title> |
<title>crc32</title> |
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<h1>crc32</h1> |
<h1>crc32</h1> |
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<p> |
<p> |
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Calculates the CRC-32 of a string or a file. |
Calculates the CRC-32 of a string or a file. |
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</p> |
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<pre class="macro-syntax"> |
<pre class="macro-syntax"> |
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crc32 <intvar> <string> |
crc32 <intvar> <string> |
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crc32file <intvar> <filename> |
crc32file <intvar> <filename> |
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</pre> |
</pre> |
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<h2>Remarks</h2> |
<h2>Remarks</h2> |
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<p> |
<p> |
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This macro function calculates the CRC(Cyclic Redundancy Checking) of a string or a file. The polynomial expression(right rotation) is as follows: |
This macro function calculates the CRC(Cyclic Redundancy Checking) of a string or a file. The polynomial expression(right rotation) is as follows: |
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<br><br> |
<br><br> |
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100000100110000010001110110110111 (x<sup>32</sup>+x<sup>26</sup>+x<sup>23</sup>+x<sup>22</sup>+x<sup>16</sup>+x<sup>12</sup>+x<sup>11</sup>+x<sup>10</sup>+x<sup>8</sup>+x<sup>7</sup>+x<sup>5</sup>+x<sup>4</sup>+x<sup>2</sup>+x<sup>1</sup>+x<sup>0</sup>) |
100000100110000010001110110110111 (x<sup>32</sup>+x<sup>26</sup>+x<sup>23</sup>+x<sup>22</sup>+x<sup>16</sup>+x<sup>12</sup>+x<sup>11</sup>+x<sup>10</sup>+x<sup>8</sup>+x<sup>7</sup>+x<sup>5</sup>+x<sup>4</sup>+x<sup>2</sup>+x<sup>1</sup>+x<sup>0</sup>) |
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<br><br> |
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The calculated value stores the variable "intvar" as mathematical value.<br> |
The calculated value stores the variable "intvar" as mathematical value.<br> |
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</p> |
</p> |
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The CRC algorithm implementation by C language is as follows: |
The CRC algorithm implementation by C language is as follows: |
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This algorithm is often used as the Ethernet FCS(Frame Check Sequence). |
This algorithm is often used as the Ethernet FCS(Frame Check Sequence). |
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<pre> |
<pre> |
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<code> |
<code> |
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#define CRCPOLY2 0xEDB88320UL /* left-right reversal */ |
#define CRCPOLY2 0xEDB88320UL /* left-right reversal */ |
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static unsigned long crc2(int n, unsigned char c[]) |
static unsigned long crc2(int n, unsigned char c[]) |
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{ |
{ |
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int i, j; |
int i, j; |
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unsigned long r; |
unsigned long r; |
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r = 0xFFFFFFFFUL; |
r = 0xFFFFFFFFUL; |
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for (i = 0; i < n; i++) { |
for (i = 0; i < n; i++) { |
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r ^= c[i]; |
r ^= c[i]; |
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for (j = 0; j < CHAR_BIT; j++) |
for (j = 0; j < CHAR_BIT; j++) |
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if (r & 1) r = (r >> 1) ^ CRCPOLY2; |
if (r & 1) r = (r >> 1) ^ CRCPOLY2; |
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else r >>= 1; |
else r >>= 1; |
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} |
} |
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return r ^ 0xFFFFFFFFUL; |
return r ^ 0xFFFFFFFFUL; |
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} |
} |
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</code></pre> |
</code></pre> |
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<h2>Example</h2> |
<h2>Example</h2> |
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<pre class="macro-example"> |
<pre class="macro-example"> |
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str = 'this is a test string to be CRC32ed' |
str = 'this is a test string to be CRC32ed' |
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crc32 crc str |
crc32 crc str |
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; Display CRC32 result asHEX |
; Display CRC32 result asHEX |
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sprintf '0x%08X' crc |
sprintf '0x%08X' crc |
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messagebox inputstr 'CRC32 = ' |
messagebox inputstr 'CRC32 = ' |
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crc32file crc 'foo.bin' |
crc32file crc 'foo.bin' |
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if result = -1 then |
if result = -1 then |
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messagebox 'file open error' 'CRC32 = ' |
messagebox 'file open error' 'CRC32 = ' |
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else |
else |
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sprintf '0x%08X' crc |
sprintf '0x%08X' crc |
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messagebox inputstr 'CRC32 = ' |
messagebox inputstr 'CRC32 = ' |
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endif |
endif |
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</pre> |
</pre> |
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