[builtins] Introduce proper Float64Tan operator.

src/third_party/fdlibm/fdlibm.js

Index: src/third_party/fdlibm/fdlibm.js
diff --git a/src/third_party/fdlibm/fdlibm.js b/src/third_party/fdlibm/fdlibm.js
index 4c8d201eebccec8951f1e89b19cc0617c9ee59ba..26ef126f6850ac5ef0a980decd0fe48c60956f1d 100644
--- a/src/third_party/fdlibm/fdlibm.js
+++ b/src/third_party/fdlibm/fdlibm.js
@@ -16,9 +16,6 @@
 // The following is a straightforward translation of fdlibm routines
 // by Raymond Toy (rtoy@google.com).
 
-// rempio2result is used as a container for return values of %RemPiO2. It is
-// initialized to a two-element Float64Array during genesis.
-
 (function(global, utils) {
   
 "use strict";
@@ -28,243 +25,15 @@
 // -------------------------------------------------------------------
 // Imports
 
-var GlobalFloat64Array = global.Float64Array;
 var GlobalMath = global.Math;
 var MathAbs;
 var MathExpm1;
-var NaN = %GetRootNaN();
-var rempio2result;
 
 utils.Import(function(from) {
   MathAbs = from.MathAbs;
   MathExpm1 = from.MathExpm1;
 });
 
-utils.CreateDoubleResultArray = function(global) {
-  rempio2result = new GlobalFloat64Array(2);
-};
-
-// -------------------------------------------------------------------
-
-define INVPIO2 = 6.36619772367581382433e-01;
-define PIO2_1  = 1.57079632673412561417;
-define PIO2_1T = 6.07710050650619224932e-11;
-define PIO2_2  = 6.07710050630396597660e-11;
-define PIO2_2T = 2.02226624879595063154e-21;
-define PIO2_3  = 2.02226624871116645580e-21;
-define PIO2_3T = 8.47842766036889956997e-32;
-define PIO4    = 7.85398163397448278999e-01;
-define PIO4LO  = 3.06161699786838301793e-17;
-
-// Compute k and r such that x - k*pi/2 = r where |r| < pi/4. For
-// precision, r is returned as two values y0 and y1 such that r = y0 + y1
-// to more than double precision.
-
-macro REMPIO2(X)
-  var n, y0, y1;
-  var hx = %_DoubleHi(X);
-  var ix = hx & 0x7fffffff;
-
-  if (ix < 0x4002d97c) {
-    // |X| ~< 3*pi/4, special case with n = +/- 1
-    if (hx > 0) {
-      var z = X - PIO2_1;
-      if (ix != 0x3ff921fb) {
-        // 33+53 bit pi is good enough
-        y0 = z - PIO2_1T;
-        y1 = (z - y0) - PIO2_1T;
-      } else {
-        // near pi/2, use 33+33+53 bit pi
-        z -= PIO2_2;
-        y0 = z - PIO2_2T;
-        y1 = (z - y0) - PIO2_2T;
-      }
-      n = 1;
-    } else {
-      // Negative X
-      var z = X + PIO2_1;
-      if (ix != 0x3ff921fb) {
-        // 33+53 bit pi is good enough
-        y0 = z + PIO2_1T;
-        y1 = (z - y0) + PIO2_1T;
-      } else {
-        // near pi/2, use 33+33+53 bit pi
-        z += PIO2_2;
-        y0 = z + PIO2_2T;
-        y1 = (z - y0) + PIO2_2T;
-      }
-      n = -1;
-    }
-  } else if (ix <= 0x413921fb) {
-    // |X| ~<= 2^19*(pi/2), medium size
-    var t = MathAbs(X);
-    n = (t * INVPIO2 + 0.5) | 0;
-    var r = t - n * PIO2_1;
-    var w = n * PIO2_1T;
-    // First round good to 85 bit
-    y0 = r - w;
-    if (ix - (%_DoubleHi(y0) & 0x7ff00000) > 0x1000000) {
-      // 2nd iteration needed, good to 118
-      t = r;
-      w = n * PIO2_2;
-      r = t - w;
-      w = n * PIO2_2T - ((t - r) - w);
-      y0 = r - w;
-      if (ix - (%_DoubleHi(y0) & 0x7ff00000) > 0x3100000) {
-        // 3rd iteration needed. 151 bits accuracy
-        t = r;
-        w = n * PIO2_3;
-        r = t - w;
-        w = n * PIO2_3T - ((t - r) - w);
-        y0 = r - w;
-      }
-    }
-    y1 = (r - y0) - w;
-    if (hx < 0) {
-      n = -n;
-      y0 = -y0;
-      y1 = -y1;
-    }
-  } else {
-    // Need to do full Payne-Hanek reduction here.
-    n = %RemPiO2(X, rempio2result);
-    y0 = rempio2result[0];
-    y1 = rempio2result[1];
-  }
-endmacro
-
-
-// kernel tan function on [-pi/4, pi/4], pi/4 ~ 0.7854
-// Input x is assumed to be bounded by ~pi/4 in magnitude.
-// Input y is the tail of x.
-// Input k indicates whether ieee_tan (if k = 1) or -1/tan (if k = -1)
-// is returned.
-//
-// Algorithm
-//  1. Since ieee_tan(-x) = -ieee_tan(x), we need only to consider positive x.
-//  2. if x < 2^-28 (hx<0x3e300000 0), return x with inexact if x!=0.
-//  3. ieee_tan(x) is approximated by a odd polynomial of degree 27 on
-//     [0,0.67434]
-//                           3             27
-//          tan(x) ~ x + T1*x + ... + T13*x
-//     where
-//
-//     |ieee_tan(x)    2     4            26   |     -59.2
-//     |----- - (1+T1*x +T2*x +.... +T13*x    )| <= 2
-//     |  x                                    |
-//
-//     Note: ieee_tan(x+y) = ieee_tan(x) + tan'(x)*y
-//                    ~ ieee_tan(x) + (1+x*x)*y
-//     Therefore, for better accuracy in computing ieee_tan(x+y), let
-//               3      2      2       2       2
-//          r = x *(T2+x *(T3+x *(...+x *(T12+x *T13))))
-//     then
-//                              3    2
-//          tan(x+y) = x + (T1*x + (x *(r+y)+y))
-//
-//  4. For x in [0.67434,pi/4],  let y = pi/4 - x, then
-//          tan(x) = ieee_tan(pi/4-y) = (1-ieee_tan(y))/(1+ieee_tan(y))
-//                 = 1 - 2*(ieee_tan(y) - (ieee_tan(y)^2)/(1+ieee_tan(y)))
-//
-// Set returnTan to 1 for tan; -1 for cot.  Anything else is illegal
-// and will cause incorrect results.
-//
-define T00 = 3.33333333333334091986e-01;
-define T01 = 1.33333333333201242699e-01;
-define T02 = 5.39682539762260521377e-02;
-define T03 = 2.18694882948595424599e-02;
-define T04 = 8.86323982359930005737e-03;
-define T05 = 3.59207910759131235356e-03;
-define T06 = 1.45620945432529025516e-03;
-define T07 = 5.88041240820264096874e-04;
-define T08 = 2.46463134818469906812e-04;
-define T09 = 7.81794442939557092300e-05;
-define T10 = 7.14072491382608190305e-05;
-define T11 = -1.85586374855275456654e-05;
-define T12 = 2.59073051863633712884e-05;
-
-function KernelTan(x, y, returnTan) {
-  var z;
-  var w;
-  var hx = %_DoubleHi(x);
-  var ix = hx & 0x7fffffff;
-
-  if (ix < 0x3e300000) {  // |x| < 2^-28
-    if (((ix | %_DoubleLo(x)) | (returnTan + 1)) == 0) {
-      // x == 0 && returnTan = -1
-      return 1 / MathAbs(x);
-    } else {
-      if (returnTan == 1) {
-        return x;
-      } else {
-        // Compute -1/(x + y) carefully
-        var w = x + y;
-        var z = %_ConstructDouble(%_DoubleHi(w), 0);
-        var v = y - (z - x);
-        var a = -1 / w;
-        var t = %_ConstructDouble(%_DoubleHi(a), 0);
-        var s = 1 + t * z;
-        return t + a * (s + t * v);
-      }
-    }
-  }
-  if (ix >= 0x3fe59428) {  // |x| > .6744
-    if (x < 0) {
-      x = -x;
-      y = -y;
-    }
-    z = PIO4 - x;
-    w = PIO4LO - y;
-    x = z + w;
-    y = 0;
-  }
-  z = x * x;
-  w = z * z;
-
-  // Break x^5 * (T1 + x^2*T2 + ...) into
-  // x^5 * (T1 + x^4*T3 + ... + x^20*T11) +
-  // x^5 * (x^2 * (T2 + x^4*T4 + ... + x^22*T12))
-  var r = T01 + w * (T03 + w * (T05 +
-                w * (T07 + w * (T09 + w * T11))));
-  var v = z * (T02 + w * (T04 + w * (T06 +
-                     w * (T08 + w * (T10 + w * T12)))));
-  var s = z * x;
-  r = y + z * (s * (r + v) + y);
-  r = r + T00 * s;
-  w = x + r;
-  if (ix >= 0x3fe59428) {
-    return (1 - ((hx >> 30) & 2)) *
-      (returnTan - 2.0 * (x - (w * w / (w + returnTan) - r)));
-  }
-  if (returnTan == 1) {
-    return w;
-  } else {
-    z = %_ConstructDouble(%_DoubleHi(w), 0);
-    v = r - (z - x);
-    var a = -1 / w;
-    var t = %_ConstructDouble(%_DoubleHi(a), 0);
-    s = 1 + t * z;
-    return t + a * (s + t * v);
-  }
-}
-
-// ECMA 262 - 15.8.2.18
-function MathTan(x) {
-  x = x * 1;  // Convert to number.
-  if ((%_DoubleHi(x) & 0x7fffffff) <= 0x3fe921fb) {
-    // |x| < pi/4, approximately.  No reduction needed.
-    return KernelTan(x, 0, 1);
-  }
-  REMPIO2(x);
-  return KernelTan(y0, y1, (n & 1) ? -1 : 1);
-}
-
-define LN2_HI    = 6.93147180369123816490e-01;
-define LN2_LO    = 1.90821492927058770002e-10;
-
-// 2^54
-define TWO54 = 18014398509481984;
-
 // ES6 draft 09-27-13, section 20.2.2.30.
 // Math.sinh
 // Method :
@@ -426,7 +195,6 @@ function MathTanh(x) {
 //-------------------------------------------------------------------
 
 utils.InstallFunctions(GlobalMath, DONT_ENUM, [
-  "tan", MathTan,
   "sinh", MathSinh,
   "cosh", MathCosh,
   "tanh", MathTanh