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Harmony: implement Math.cbrt in Javascript.

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R=jarin@chromium.org

Review URL: https://codereview.chromium.org/183743018

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19742 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
yangguo@chromium.org 2014-03-10 08:21:18 +00:00
parent 2c74163f59
commit 4826aa7af2
3 changed files with 20 additions and 32 deletions
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21
src/harmony-math.js
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@ -175,10 +175,29 @@ function MathClz32(x) {
// ES6 draft 09-27-13, section 20.2.2.9.
// Cube root approximation, refer to: http://metamerist.com/cbrt/cbrt.htm
// Using initial approximation adapted from Kahan's cbrt and 4 iterations
// of Newton's method.
function MathCbrt(x) {
return %Math_cbrt(TO_NUMBER_INLINE(x));
if (!IS_NUMBER(x)) x = NonNumberToNumber(x);
if (x == 0 || !NUMBER_IS_FINITE(x)) return x;
return x >= 0 ? CubeRoot(x) : -CubeRoot(-x);
}
macro NEWTON_ITERATION_CBRT(x, approx)
(1.0 / 3.0) * (x / (approx * approx) + 2 * approx);
endmacro
function CubeRoot(x) {
var approx_hi = MathFloor(%_DoubleHi(x) / 3) + 0x2A9F7893;
var approx = %_ConstructDouble(approx_hi, 0);
approx = NEWTON_ITERATION_CBRT(x, approx);
approx = NEWTON_ITERATION_CBRT(x, approx);
approx = NEWTON_ITERATION_CBRT(x, approx);
return NEWTON_ITERATION_CBRT(x, approx);
}
// ES6 draft 09-27-13, section 20.2.2.14.
// Use Taylor series to approximate.

30
src/runtime.cc
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@ -7694,36 +7694,6 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_ConstructDouble) {
}
// Cube root approximation, refer to: http://metamerist.com/cbrt/cbrt.htm
// Using initial approximation adapted from Kahan's cbrt and 4 iterations
// of Newton's method.
inline double CubeRootNewtonIteration(double approx, double x) {
return (1.0 / 3.0) * (x / (approx * approx) + 2 * approx);
}
inline double CubeRoot(double x) {
static const uint64_t magic = V8_2PART_UINT64_C(0x2A9F7893, 00000000);
uint64_t xhigh = double_to_uint64(x);
double approx = uint64_to_double(xhigh / 3 + magic);
approx = CubeRootNewtonIteration(approx, x);
approx = CubeRootNewtonIteration(approx, x);
approx = CubeRootNewtonIteration(approx, x);
return CubeRootNewtonIteration(approx, x);
}
RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_cbrt) {
SealHandleScope shs(isolate);
ASSERT(args.length() == 1);
CONVERT_DOUBLE_ARG_CHECKED(x, 0);
if (x == 0 || std::isinf(x)) return args[0];
double result = (x > 0) ? CubeRoot(x) : -CubeRoot(-x);
return isolate->heap()->AllocateHeapNumber(result);
}
static const double kPiDividedBy4 = 0.78539816339744830962;

1
src/runtime.h
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@ -175,7 +175,6 @@ namespace internal {
F(Math_asin, 1, 1) \
F(Math_atan, 1, 1) \
F(Math_log, 1, 1) \
F(Math_cbrt, 1, 1) \
F(Math_sqrt, 1, 1) \
F(Math_exp, 1, 1) \
F(Math_floor, 1, 1) \