js/src/t/bitops-3bit-bits-in-byte.js

   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);