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Small space-saving optimisation

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git-svn-id: https://svn.code.sf.net/p/nsis/code/NSIS/trunk@687 212acab6-be3b-0410-9dea-997c60f758d6
This commit is contained in:
eccles 2002-08-11 18:58:41 +00:00
parent 8b9d432f7e
commit c05a873977
2 changed files with 25 additions and 30 deletions
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39
Source/crc32.c
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@ -2,33 +2,28 @@
#ifdef NSIS_CONFIG_CRC_SUPPORT
// this is based on the (slow,small) CRC32 implementation from zlib.
static unsigned long crc_table[256];
static void make_crc_table()
{
unsigned long c;
int n, k;
for (n = 0; n < 256; n++)
{
c = (unsigned long)n;
for (k = 0; k < 8; k++) c = (c >> 1) ^ (c & 1 ? 0xedb88320L : 0);
crc_table[n] = c;
}
}
// actually CRC32, but we put it in here so we don't
// have to modify the other code.
unsigned long CRC32(unsigned long crc, const unsigned char *buf, unsigned int len)
{
if (!crc_table[1]) make_crc_table();
static unsigned long crc_table[256];
if (!crc_table[1])
{
unsigned long c;
int n, k;
for (n = 0; n < 256; n++)
{
c = (unsigned long)n;
for (k = 0; k < 8; k++) c = (c >> 1) ^ (c & 1 ? 0xedb88320L : 0);
crc_table[n] = c;
}
}
crc = crc ^ 0xffffffffL;
while (len-- > 0) {
crc = crc_table[(crc ^ (*buf++)) & 0xff] ^ (crc >> 8);
crc = crc_table[(crc ^ (*buf++)) & 0xff] ^ (crc >> 8);
}
return crc ^ 0xffffffffL;
}
#endif
#endif