[builtins] Unify Atanh, Cbrt and Expm1 as exports from flibm.

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 935b777b316cf47ad82d679104bb99be22ad1211..de7133405bc83620da60eb972557a6ed0d44d74d 100644
--- a/src/third_party/fdlibm/fdlibm.js
+++ b/src/third_party/fdlibm/fdlibm.js
@@ -31,11 +31,13 @@
 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) {
@@ -401,202 +403,6 @@ define LN2_LO    = 1.90821492927058770002e-10;
 // 2^54
 define TWO54 = 18014398509481984;
 
-// ES6 draft 09-27-13, section 20.2.2.14.
-// Math.expm1
-// Returns exp(x)-1, the exponential of x minus 1.
-//
-// Method
-//   1. Argument reduction:
-//      Given x, find r and integer k such that
-//
-//               x = k*ln2 + r,  |r| <= 0.5*ln2 ~ 0.34658  
-//
-//      Here a correction term c will be computed to compensate 
-//      the error in r when rounded to a floating-point number.
-//
-//   2. Approximating expm1(r) by a special rational function on
-//      the interval [0,0.34658]:
-//      Since
-//          r*(exp(r)+1)/(exp(r)-1) = 2+ r^2/6 - r^4/360 + ...
-//      we define R1(r*r) by
-//          r*(exp(r)+1)/(exp(r)-1) = 2+ r^2/6 * R1(r*r)
-//      That is,
-//          R1(r**2) = 6/r *((exp(r)+1)/(exp(r)-1) - 2/r)
-//                   = 6/r * ( 1 + 2.0*(1/(exp(r)-1) - 1/r))
-//                   = 1 - r^2/60 + r^4/2520 - r^6/100800 + ...
-//      We use a special Remes algorithm on [0,0.347] to generate 
-//      a polynomial of degree 5 in r*r to approximate R1. The 
-//      maximum error of this polynomial approximation is bounded 
-//      by 2**-61. In other words,
-//          R1(z) ~ 1.0 + Q1*z + Q2*z**2 + Q3*z**3 + Q4*z**4 + Q5*z**5
-//      where   Q1  =  -1.6666666666666567384E-2,
-//              Q2  =   3.9682539681370365873E-4,
-//              Q3  =  -9.9206344733435987357E-6,
-//              Q4  =   2.5051361420808517002E-7,
-//              Q5  =  -6.2843505682382617102E-9;
-//      (where z=r*r, and the values of Q1 to Q5 are listed below)
-//      with error bounded by
-//          |                  5           |     -61
-//          | 1.0+Q1*z+...+Q5*z   -  R1(z) | <= 2 
-//          |                              |
-//
-//      expm1(r) = exp(r)-1 is then computed by the following 
-//      specific way which minimize the accumulation rounding error: 
-//                             2     3
-//                            r     r    [ 3 - (R1 + R1*r/2)  ]
-//            expm1(r) = r + --- + --- * [--------------------]
-//                            2     2    [ 6 - r*(3 - R1*r/2) ]
-//
-//      To compensate the error in the argument reduction, we use
-//              expm1(r+c) = expm1(r) + c + expm1(r)*c 
-//                         ~ expm1(r) + c + r*c 
-//      Thus c+r*c will be added in as the correction terms for
-//      expm1(r+c). Now rearrange the term to avoid optimization 
-//      screw up:
-//                      (      2                                    2 )
-//                      ({  ( r    [ R1 -  (3 - R1*r/2) ]  )  }    r  )
-//       expm1(r+c)~r - ({r*(--- * [--------------------]-c)-c} - --- )
-//                      ({  ( 2    [ 6 - r*(3 - R1*r/2) ]  )  }    2  )
-//                      (                                             )
-//
-//                 = r - E
-//   3. Scale back to obtain expm1(x):
-//      From step 1, we have
-//         expm1(x) = either 2^k*[expm1(r)+1] - 1
-//                  = or     2^k*[expm1(r) + (1-2^-k)]
-//   4. Implementation notes:
-//      (A). To save one multiplication, we scale the coefficient Qi
-//           to Qi*2^i, and replace z by (x^2)/2.
-//      (B). To achieve maximum accuracy, we compute expm1(x) by
-//        (i)   if x < -56*ln2, return -1.0, (raise inexact if x!=inf)
-//        (ii)  if k=0, return r-E
-//        (iii) if k=-1, return 0.5*(r-E)-0.5
-//        (iv)  if k=1 if r < -0.25, return 2*((r+0.5)- E)
-//                     else          return  1.0+2.0*(r-E);
-//        (v)   if (k<-2||k>56) return 2^k(1-(E-r)) - 1 (or exp(x)-1)
-//        (vi)  if k <= 20, return 2^k((1-2^-k)-(E-r)), else
-//        (vii) return 2^k(1-((E+2^-k)-r)) 
-//
-// Special cases:
-//      expm1(INF) is INF, expm1(NaN) is NaN;
-//      expm1(-INF) is -1, and
-//      for finite argument, only expm1(0)=0 is exact.
-//
-// Accuracy:
-//      according to an error analysis, the error is always less than
-//      1 ulp (unit in the last place).
-//
-// Misc. info.
-//      For IEEE double 
-//          if x > 7.09782712893383973096e+02 then expm1(x) overflow
-//
-define KEXPM1_OVERFLOW = 7.09782712893383973096e+02;
-define INVLN2          = 1.44269504088896338700;
-define EXPM1_1 = -3.33333333333331316428e-02;
-define EXPM1_2 = 1.58730158725481460165e-03;
-define EXPM1_3 = -7.93650757867487942473e-05;
-define EXPM1_4 = 4.00821782732936239552e-06;
-define EXPM1_5 = -2.01099218183624371326e-07;
-
-function MathExpm1(x) {
-  x = x * 1;  // Convert to number.
-  var y;
-  var hi;
-  var lo;
-  var k;
-  var t;
-  var c;
-    
-  var hx = %_DoubleHi(x);
-  var xsb = hx & 0x80000000;     // Sign bit of x
-  var y = (xsb === 0) ? x : -x;  // y = |x|
-  hx &= 0x7fffffff;              // High word of |x|
-
-  // Filter out huge and non-finite argument
-  if (hx >= 0x4043687a) {     // if |x| ~=> 56 * ln2
-    if (hx >= 0x40862e42) {   // if |x| >= 709.78
-      if (hx >= 0x7ff00000) {
-        // expm1(inf) = inf; expm1(-inf) = -1; expm1(nan) = nan;
-        return (x === -INFINITY) ? -1 : x;
-      }
-      if (x > KEXPM1_OVERFLOW) return INFINITY;  // Overflow
-    }
-    if (xsb != 0) return -1;  // x < -56 * ln2, return -1.
-  }
-
-  // Argument reduction
-  if (hx > 0x3fd62e42) {    // if |x| > 0.5 * ln2
-    if (hx < 0x3ff0a2b2) {  // and |x| < 1.5 * ln2
-      if (xsb === 0) {
-        hi = x - LN2_HI;
-        lo = LN2_LO;
-        k = 1;
-      } else {
-        hi = x + LN2_HI;
-        lo = -LN2_LO;
-        k = -1;
-      }
-    } else {
-      k = (INVLN2 * x + ((xsb === 0) ? 0.5 : -0.5)) | 0;
-      t = k;
-      // t * ln2_hi is exact here.
-      hi = x - t * LN2_HI;
-      lo = t * LN2_LO;
-    }
-    x = hi - lo;
-    c = (hi - x) - lo;
-  } else if (hx < 0x3c900000)	{
-    // When |x| < 2^-54, we can return x.
-    return x;
-  } else {
-    // Fall through.
-    k = 0;
-  }
-
-  // x is now in primary range
-  var hfx = 0.5 * x;
-  var hxs = x * hfx;
-  var r1 = 1 + hxs * (EXPM1_1 + hxs * (EXPM1_2 + hxs *
-                     (EXPM1_3 + hxs * (EXPM1_4 + hxs * EXPM1_5))));
-  t = 3 - r1 * hfx;
-  var e = hxs * ((r1 - t) / (6 - x * t));
-  if (k === 0) {  // c is 0
-    return x - (x*e - hxs);
-  } else {
-    e = (x * (e - c) - c);
-    e -= hxs;
-    if (k === -1) return 0.5 * (x - e) - 0.5;
-    if (k === 1) {
-      if (x < -0.25) return -2 * (e - (x + 0.5));
-      return 1 + 2 * (x - e);
-    }
-
-    if (k <= -2 || k > 56) {
-      // suffice to return exp(x) + 1
-      y = 1 - (e - x);
-      // Add k to y's exponent
-      y = %_ConstructDouble(%_DoubleHi(y) + (k << 20), %_DoubleLo(y));
-      return y - 1;
-    }
-    if (k < 20) {
-      // t = 1 - 2^k
-      t = %_ConstructDouble(0x3ff00000 - (0x200000 >> k), 0);
-      y = t - (e - x);
-      // Add k to y's exponent
-      y = %_ConstructDouble(%_DoubleHi(y) + (k << 20), %_DoubleLo(y));
-    } else {
-      // t = 2^-k
-      t = %_ConstructDouble((0x3ff - k) << 20, 0);
-      y = x - (e + t);
-      y += 1;
-      // Add k to y's exponent
-      y = %_ConstructDouble(%_DoubleHi(y) + (k << 20), %_DoubleLo(y));
-    }
-  }
-  return y;
-}
-
-
 // ES6 draft 09-27-13, section 20.2.2.30.
 // Math.sinh
 // Method :
@@ -763,8 +569,7 @@ utils.InstallFunctions(GlobalMath, DONT_ENUM, [
   "tan", MathTan,
   "sinh", MathSinh,
   "cosh", MathCosh,
-  "tanh", MathTanh,
-  "expm1", MathExpm1
+  "tanh", MathTanh
 ]);
 
 %SetForceInlineFlag(MathSin);