2013-09-28 05:30:57 +00:00
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<div class="pd w0 h0"><div id="pf5" class="pf" data-page-no="5"><div class="pc pc5"><img class="bi x2f y141 w5 h11" alt="" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAO8AAAABCAIAAAC5XG4cAAAACXBIWXMAABYlAAAWJQFJUiTwAAAAD0lEQVQoz2NgGAWjYLgAAALOAAHc7AMEAAAAAElFTkSuQmCC"/><div class="t m0 x2f h5 y5b ff2 fs3 fc0 sc0 ls0 ws0">resentations<span class="_ _8"> </span>are<span class="_ _8"> </span>assigned<span class="_ _6"> </span>an<span class="_ _8"> </span>integer<span class="_ _8"> </span>key<span class="_ _6"> </span>called<span class="_ _8"> </span>the<span class="_ _8"> </span><span class="ffa">object<span class="_ _8"> </span>shape</span>.</div><div class="t m0 x2f h5 y5c ff2 fs3 fc0 sc0 ls0 ws0">Thus,<span class="_ _5"> </span>the<span class="_ _5"> </span>guard<span class="_ _3"> </span>is<span class="_ _5"> </span>a<span class="_ _5"> </span>simple<span class="_ _5"> </span>equality<span class="_ _5"> </span>check<span class="_ _5"> </span>on<span class="_ _5"> </span>the<span class="_ _3"> </span>object<span class="_ _5"> </span>shape.</div><div class="t m0 x34 h5 y5d ff1 fs3 fc0 sc0 ls0 ws0">Representation<span class="_ _d"> </span>specialization:<span class="_ _d"> </span>numbers.<span class="_ _1"> </span><span class="ff2">Ja<span class="_ _2"></span>v<span class="_ _2"></span>aScript<span class="_ _d"> </span>has<span class="_ _d"> </span>no</span></div><div class="t m0 x2f h5 y5e ff2 fs3 fc0 sc0 ls0 ws0">integer<span class="_ _6"> </span>type,<span class="_ _6"> </span>only<span class="_ _8"> </span>a<span class="_ _8"> </span>Number<span class="_ _6"> </span>type<span class="_ _8"> </span>that<span class="_ _8"> </span>is<span class="_ _6"> </span>the<span class="_ _8"> </span>set<span class="_ _6"> </span>of<span class="_ _8"> </span>64-bit<span class="_ _8"> </span>IEEE-</div><div class="t m0 x2f h5 y5f ff2 fs3 fc0 sc0 ls0 ws0">754<span class="_ _1"> </span>floating-pointer<span class="_ _d"> </span>numbers<span class="_ _1"> </span>(“doubles”).<span class="_ _d"> </span>But<span class="_ _1"> </span>man<span class="_ _2"></span>y<span class="_ _d"> </span>JavaScript</div><div class="t m0 x2f h5 y60 ff2 fs3 fc0 sc0 ls0 ws0">operators,<span class="_ _5"> </span>in<span class="_ _3"> </span>particular<span class="_ _5"> </span>array<span class="_ _5"> </span>accesses<span class="_ _5"> </span>and<span class="_ _3"> </span>bitwise<span class="_ _5"> </span>operators,<span class="_ _5"> </span>really</div><div class="t m0 x2f h5 y61 ff2 fs3 fc0 sc0 ls0 ws0">operate<span class="_ _3"> </span>on<span class="_ _3"> </span>inte<span class="_ _2"></span>gers,<span class="_ _3"> </span>so<span class="_ _3"> </span>the<span class="_ _2"></span>y<span class="_ _3"> </span>first<span class="_ _3"> </span>con<span class="_ _2"></span>v<span class="_ _2"></span>ert<span class="_ _3"> </span>the<span class="_ _5"> </span>number<span class="_ _3"> </span>to<span class="_ _3"> </span>an<span class="_ _3"> </span>integer<span class="_ _2"></span>,</div><div class="t m0 x2f h5 y62 ff2 fs3 fc0 sc0 ls0 ws0">and<span class="_ _6"> </span>then<span class="_ _8"> </span>con<span class="_ _2"></span>vert<span class="_ _6"> </span>any<span class="_ _6"> </span>integer<span class="_ _6"> </span>result<span class="_ _6"> </span>back<span class="_ _8"> </span>to<span class="_ _8"> </span>a<span class="_ _6"> </span>double.</div><div class="t m0 x63 h8 y142 ff2 fs4 fc0 sc0 ls0 ws0">1</div><div class="t m0 x6 h5 y62 ff2 fs3 fc0 sc0 ls0 ws0">Clearly<span class="_ _2"></span>,<span class="_ _6"> </span>a</div><div class="t m0 x2f h5 y63 ff2 fs3 fc0 sc0 ls0 ws0">Jav<span class="_ _2"></span>aScript<span class="_ _5"> </span>VM<span class="_ _3"> </span>that<span class="_ _3"> </span>w<span class="_ _2"></span>ants<span class="_ _3"> </span>to<span class="_ _5"> </span>be<span class="_ _3"> </span>f<span class="_ _2"></span>ast<span class="_ _3"> </span>must<span class="_ _5"> </span>find<span class="_ _3"> </span>a<span class="_ _5"> </span>way<span class="_ _3"> </span>to<span class="_ _3"> </span>operate<span class="_ _5"> </s
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