Slow thread right now. Need posters!
Ok I'll post some memories this coin has dredged up from the past.
A little trick for those 32bit CPU's without hardware division (like most ARM) for calculating mod 17 (correctness tested for all values 0 to 0xffffffff):
// 32 = 2^5 ; (2^32 / 17) = 252645135.05882352941176470588 ~= 0x0f0f0f0f
uint32_t mod17(uint32_t n) {
static uint8_t table[32] = { 0 ,1 ,2 ,2 ,3 ,3 ,4 ,4 ,
5 ,5 ,6 ,6 ,7 ,7 ,8 ,8 ,
9 ,9 ,10,10,11,11,12,12,
13,13,14,14,15,15,16,16 };
n = (0x0f0f0f0f*n + (n >> 4)) >> 27;
return table[n];
}
While it is only marginally (a few %) quicker than the abi version gcc uses it was fun to rediscover. Strangely removing the table lookup makes it slower (which I didn't expect).
Bump.
--
bsunau7
