Harmony: implement Math.clz32

src/harmony-math.js

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 //
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@@ skipping 136 matching lines @@
     var n = args[i] / max;
     var summand = n * n - compensation;
     var preliminary = sum + summand;
     compensation = (preliminary - sum) - summand;
     sum = preliminary;
   }
   return MathSqrt(sum) * max;
 }
 
 
+function MathClz32(x) {

[Sven Panne, 2014/02/18 07:21:24]

What TC39 seems to intend is basically exposing some form of intrinsics for
processor intstructions. AFAICT "count leading zeroes" has HW support for all
our platforms and boils down to a single CPU instructions, and I think this is
the expectation of people using such intrinsics. Therefore we should add
Crankshaft support, which shouldn't be too hard.

+  x = ToUint32(TO_NUMBER_INLINE(x));
+  if (x == 0) return 32;
+  var result = 0;
+  // Binary search.
+  if ((x & 0xFFFF0000) === 0) { x <<= 16; result += 16; };
+  if ((x & 0xFF000000) === 0) { x <<=  8; result +=  8; };
+  if ((x & 0xF0000000) === 0) { x <<=  4; result +=  4; };
+  if ((x & 0xC0000000) === 0) { x <<=  2; result +=  2; };
+  if ((x & 0x80000000) === 0) { x <<=  1; result +=  1; };
+  return result;
+}
+
+
 function ExtendMath() {
   %CheckIsBootstrapping();
 
   // Set up the non-enumerable functions on the Math object.
   InstallFunctions($Math, DONT_ENUM, $Array(
     "sign", MathSign,
     "trunc", MathTrunc,
     "sinh", MathSinh,
     "cosh", MathCosh,
     "tanh", MathTanh,
     "asinh", MathAsinh,
     "acosh", MathAcosh,
     "atanh", MathAtanh,
     "log10", MathLog10,
     "log2", MathLog2,
-    "hypot", MathHypot
+    "hypot", MathHypot,
+    "clz32", MathClz32
   ));
 }
 
+
 ExtendMath();