1 // Copyright (c) 2004 by Arthur Langereis (arthur_ext at domain xfinitegames, tld com 2 3 // 1 op = 6 ANDs, 3 SHRs, 3 SHLs, 4 assigns, 2 ADDs 4 // O(1) 5 function fast3bitlookup(b) { 6 var c, bi3b = 0xE994; // 0b1110 1001 1001 0100; // 3 2 2 1 2 1 1 0 7 c = 3 & (bi3b >> ((b << 1) & 14)); 8 c += 3 & (bi3b >> ((b >> 2) & 14)); 9 c += 3 & (bi3b >> ((b >> 5) & 6)); 10 return c; 11 12 /* 13 lir4,0xE994; 9 instructions, no memory access, minimal register dependence, 6 shifts, 2 adds, 1 inline assign 14 rlwinmr5,r3,1,28,30 15 rlwinmr6,r3,30,28,30 16 rlwinmr7,r3,27,29,30 17 rlwnmr8,r4,r5,30,31 18 rlwnmr9,r4,r6,30,31 19 rlwnmr10,r4,r7,30,31 20 addr3,r8,r9 21 addr3,r3,r10 22 */ 23 } 24 25 26 function TimeFunc(func) { 27 var x, y, t; 28 for(var x=0; x<500; x++) 29 for(var y=0; y<256; y++) func(y); 30 } 31 32 TimeFunc(fast3bitlookup); 33
