fpizlo@apple.com | b144d21 | 2013-09-05 02:53:16 +0000 | [diff] [blame^] | 1 | // Copyright (c) 2004 by Arthur Langereis (arthur_ext at domain xfinitegames, tld com |
| 2 | |
| 3 | var result = 0; |
| 4 | |
| 5 | // 1 op = 6 ANDs, 3 SHRs, 3 SHLs, 4 assigns, 2 ADDs |
| 6 | // O(1) |
| 7 | function fast3bitlookup(b) { |
| 8 | var c, bi3b = 0xE994; // 0b1110 1001 1001 0100; // 3 2 2 1 2 1 1 0 |
| 9 | c = 3 & (bi3b >> ((b << 1) & 14)); |
| 10 | c += 3 & (bi3b >> ((b >> 2) & 14)); |
| 11 | c += 3 & (bi3b >> ((b >> 5) & 6)); |
| 12 | return c; |
| 13 | |
| 14 | /* |
| 15 | lir4,0xE994; 9 instructions, no memory access, minimal register dependence, 6 shifts, 2 adds, 1 inline assign |
| 16 | rlwinmr5,r3,1,28,30 |
| 17 | rlwinmr6,r3,30,28,30 |
| 18 | rlwinmr7,r3,27,29,30 |
| 19 | rlwnmr8,r4,r5,30,31 |
| 20 | rlwnmr9,r4,r6,30,31 |
| 21 | rlwnmr10,r4,r7,30,31 |
| 22 | addr3,r8,r9 |
| 23 | addr3,r3,r10 |
| 24 | */ |
| 25 | } |
| 26 | |
| 27 | |
| 28 | function TimeFunc(func) { |
| 29 | var x, y, t; |
| 30 | var sum = 0; |
| 31 | for(var x=0; x<50000; x++) |
| 32 | for(var y=0; y<256; y++) sum += func(y); |
| 33 | return sum; |
| 34 | } |
| 35 | |
| 36 | sum = TimeFunc(fast3bitlookup); |
| 37 | |
| 38 | var expected = 51200000; |
| 39 | if (sum != expected) |
| 40 | throw "ERROR: bad result: expected " + expected + " but got " + sum; |