use pregenerated CRC32 lookup tables for retain on Win32 and GNU/Linux

This code could be possible reused on low-end targets with limited RAM.

code to generate lookup table:
[---------------------------------------------------------------------]

/* CRC lookup table and initial state. */
uint32_t crc32_table[256];

/* Generate CRC32 lookup table. */
void GenerateCRC32Table(void)
{
unsigned int i, j;
/* Use CRC-32-IEEE 802.3 polynomial 0x04C11DB7 (bit reflected). */
uint32_t poly = 0xEDB88320;

for (i = 0; i <= 0xFF; i++)
{
uint32_t c = i;
for (j = 0 ; j < 8 ; j++)
c = (c & 1) ? (c >> 1 ) ^ poly : (c >> 1);
crc32_table[i] = c;
}
}

void main(void)
{
GenerateCRC32Table();
int j=0;
for(int i=0; i<256; i++) {
printf("0x%08X, ", crc32_table[i]);
if (++j >= 8) {
j = 0;
printf("\n");
}
}
}
[---------------------------------------------------------------------]

     1

<?xml version='1.0' encoding='utf-8'?>

     2

<PyFile xmlns:xhtml="http://www.w3.org/1999/xhtml" xmlns:xsd="http://www.w3.org/2001/XMLSchema">

     3

  <variables/>

     4

  <globals>

     5

    <xhtml:p><![CDATA[import threading, time

     6

     7

MyT = None

     8

Stop = False

     9

    10

def StartLog():

    11

    global MyT

    12

    MyT=threading.Thread(target = DoLog)

    13

    MyT.start()

    14

    15

def DoLog():

    16

    global Stop

    17

    while not Stop:

    18

        PLCObject.LogMessage("Python side Logging (PLC is %s)"%PLCObject.PLCStatus)

    19

        time.sleep(0.3)

    20

    21

def StopLog():

    22

    global MyT,Stop

    23

    Stop=True

    24

    25

_runtime_init.append(StartLog)

    26

_runtime_cleanup.append(StopLog)

    27

]]></xhtml:p>

    28

  </globals>

    29

  <init>

    30

    <xhtml:p><![CDATA[]]></xhtml:p>

    31

  </init>

    32

  <cleanup>

    33

    <xhtml:p><![CDATA[]]></xhtml:p>

    34

  </cleanup>

    35

  <start>

    36

    <xhtml:p><![CDATA[]]></xhtml:p>

    37

  </start>

    38

  <stop>

    39

    <xhtml:p><![CDATA[]]></xhtml:p>

    40

  </stop>

    41

</PyFile>