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