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Update wifi.cpp - added faster reflect functions #896

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Update wifi.cpp - added faster reflect functions #896

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22 changes: 20 additions & 2 deletions desmume/src/wifi.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -346,6 +346,24 @@ static u32 reflect(u32 ref, char ch)
return value;
}

static u32 reflect8(u32 ref)
{
ref = ((ref & 0x0F) << 4) | ((ref & 0xF0) >> 4);
ref = ((ref & 0x33) << 2) | ((ref & 0xCC) >> 2);
ref = ((ref & 0x55) << 1) | ((ref & 0xAA) >> 1);
return ref;
}

static u32 reflect32(u32 ref)
{
ref = ((ref & 0x0000FFFF) << 16) | ((ref & 0xFFFF0000) >> 16);
ref = ((ref & 0x00FF00FF) << 8) | ((ref & 0xFF00FF00) >> 8);
ref = ((ref & 0x0F0F0F0F) << 4) | ((ref & 0xF0F0F0F0) >> 4);
ref = ((ref & 0x33333333) << 2) | ((ref & 0xCCCCCCCC) >> 2);
ref = ((ref & 0x55555555) << 1) | ((ref & 0xAAAAAAAA) >> 1);
return ref;
}

static u32 WIFI_calcCRC32(u8* data, int len)
{
u32 crc = 0xFFFFFFFF;
Expand All @@ -366,10 +384,10 @@ static void WIFI_initCRC32Table()

for(int i = 0; i < 0x100; i++)
{
WIFI_CRC32Table[i] = reflect(i, 8) << 24;
WIFI_CRC32Table[i] = reflect8(i) << 24;
for(int j = 0; j < 8; j++)
WIFI_CRC32Table[i] = (WIFI_CRC32Table[i] << 1) ^ (WIFI_CRC32Table[i] & (1 << 31) ? polynomial : 0);
WIFI_CRC32Table[i] = reflect(WIFI_CRC32Table[i], 32);
WIFI_CRC32Table[i] = reflect32(WIFI_CRC32Table[i]);
}
}

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