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"?>

     2

<purchaseOrder orderDate="1999-10-20">

     3

  <shipTo country="US">

     4

    <name>Alice Smith</name>

     5

    <street>123 Maple Street</street>

     6

    <city>Mill Valley</city>

     7

    <state>CA</state>

     8

    <zip>90952</zip>

     9

  </shipTo>

    10

  <billTo country="US">

    11

    <name>Robert Smith</name>

    12

    <street>8 Oak Avenue</street>

    13

    <city>Old Town</city>

    14

    <state>PA</state>

    15

    <zip>95819</zip>

    16

  </billTo>

    17

  <comment>Hurry, my lawn is going wild!</comment>

    18

  <items>

    19

    <item partNum="872-AA">

    20

      <productName>Lawnmower</productName>

    21

      <quantity>1</quantity>

    22

      <USPrice>148.95</USPrice>

    23

      <comment>Confirm this is electric</comment>

    24

    </item>

    25

    <item partNum="926-AA">

    26

      <productName>Baby Monitor</productName>

    27

      <quantity>1</quantity>

    28

      <USPrice>39.98</USPrice>

    29

      <shipDate>1999-05-21</shipDate>

    30

    </item>

    31

  </items>

    32

</purchaseOrder>