Revert of [builtins] Introduce proper Float64Exp operator.

src/base/ieee754.cc

Index: src/base/ieee754.cc
diff --git a/src/base/ieee754.cc b/src/base/ieee754.cc
index e642b6327a9b29360db3c09ebc0235b15b3c9f0e..4d11bdafe8b89e26a737a3c332f39fc7d6b45b0f 100644
--- a/src/base/ieee754.cc
+++ b/src/base/ieee754.cc
@@ -389,152 +389,6 @@
       return pi - (z - pi_lo); /* atan(+,-) */
     default:                   /* case 3 */
       return (z - pi_lo) - pi; /* atan(-,-) */
-  }
-}
-
-/* exp(x)
- * Returns the exponential of x.
- *
- * Method
- *   1. Argument reduction:
- *      Reduce x to an r so that |r| <= 0.5*ln2 ~ 0.34658.
- *      Given x, find r and integer k such that
- *
- *               x = k*ln2 + r,  |r| <= 0.5*ln2.
- *
- *      Here r will be represented as r = hi-lo for better
- *      accuracy.
- *
- *   2. Approximation of exp(r) by a special rational function on
- *      the interval [0,0.34658]:
- *      Write
- *          R(r**2) = r*(exp(r)+1)/(exp(r)-1) = 2 + r*r/6 - r**4/360 + ...
- *      We use a special Remes algorithm on [0,0.34658] to generate
- *      a polynomial of degree 5 to approximate R. The maximum error
- *      of this polynomial approximation is bounded by 2**-59. In
- *      other words,
- *          R(z) ~ 2.0 + P1*z + P2*z**2 + P3*z**3 + P4*z**4 + P5*z**5
- *      (where z=r*r, and the values of P1 to P5 are listed below)
- *      and
- *          |                  5          |     -59
- *          | 2.0+P1*z+...+P5*z   -  R(z) | <= 2
- *          |                             |
- *      The computation of exp(r) thus becomes
- *                             2*r
- *              exp(r) = 1 + -------
- *                            R - r
- *                                 r*R1(r)
- *                     = 1 + r + ----------- (for better accuracy)
- *                                2 - R1(r)
- *      where
- *                               2       4             10
- *              R1(r) = r - (P1*r  + P2*r  + ... + P5*r   ).
- *
- *   3. Scale back to obtain exp(x):
- *      From step 1, we have
- *         exp(x) = 2^k * exp(r)
- *
- * Special cases:
- *      exp(INF) is INF, exp(NaN) is NaN;
- *      exp(-INF) is 0, and
- *      for finite argument, only exp(0)=1 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 exp(x) overflow
- *          if x < -7.45133219101941108420e+02 then exp(x) underflow
- *
- * Constants:
- * The hexadecimal values are the intended ones for the following
- * constants. The decimal values may be used, provided that the
- * compiler will convert from decimal to binary accurately enough
- * to produce the hexadecimal values shown.
- */
-double exp(double x) {
-  static const double
-      one = 1.0,
-      halF[2] = {0.5, -0.5},
-      o_threshold = 7.09782712893383973096e+02,  /* 0x40862E42, 0xFEFA39EF */
-      u_threshold = -7.45133219101941108420e+02, /* 0xc0874910, 0xD52D3051 */
-      ln2HI[2] = {6.93147180369123816490e-01,    /* 0x3fe62e42, 0xfee00000 */
-                  -6.93147180369123816490e-01},  /* 0xbfe62e42, 0xfee00000 */
-      ln2LO[2] = {1.90821492927058770002e-10,    /* 0x3dea39ef, 0x35793c76 */
-                  -1.90821492927058770002e-10},  /* 0xbdea39ef, 0x35793c76 */
-      invln2 = 1.44269504088896338700e+00,       /* 0x3ff71547, 0x652b82fe */
-      P1 = 1.66666666666666019037e-01,           /* 0x3FC55555, 0x5555553E */
-      P2 = -2.77777777770155933842e-03,          /* 0xBF66C16C, 0x16BEBD93 */
-      P3 = 6.61375632143793436117e-05,           /* 0x3F11566A, 0xAF25DE2C */
-      P4 = -1.65339022054652515390e-06,          /* 0xBEBBBD41, 0xC5D26BF1 */
-      P5 = 4.13813679705723846039e-08;           /* 0x3E663769, 0x72BEA4D0 */
-
-  static volatile double
-      huge = 1.0e+300,
-      twom1000 = 9.33263618503218878990e-302, /* 2**-1000=0x01700000,0*/
-      two1023 = 8.988465674311579539e307;     /* 0x1p1023 */
-
-  double y, hi = 0.0, lo = 0.0, c, t, twopk;
-  int32_t k = 0, xsb;
-  u_int32_t hx;
-
-  GET_HIGH_WORD(hx, x);
-  xsb = (hx >> 31) & 1; /* sign bit of x */
-  hx &= 0x7fffffff;     /* high word of |x| */
-
-  /* filter out non-finite argument */
-  if (hx >= 0x40862E42) { /* if |x|>=709.78... */
-    if (hx >= 0x7ff00000) {
-      u_int32_t lx;
-      GET_LOW_WORD(lx, x);
-      if (((hx & 0xfffff) | lx) != 0)
-        return x + x; /* NaN */
-      else
-        return (xsb == 0) ? x : 0.0; /* exp(+-inf)={inf,0} */
-    }
-    if (x > o_threshold) return huge * huge;         /* overflow */
-    if (x < u_threshold) return twom1000 * twom1000; /* underflow */
-  }
-
-  /* argument reduction */
-  if (hx > 0x3fd62e42) {   /* if  |x| > 0.5 ln2 */
-    if (hx < 0x3FF0A2B2) { /* and |x| < 1.5 ln2 */
-      hi = x - ln2HI[xsb];
-      lo = ln2LO[xsb];
-      k = 1 - xsb - xsb;
-    } else {
-      k = static_cast<int>(invln2 * x + halF[xsb]);
-      t = k;
-      hi = x - t * ln2HI[0]; /* t*ln2HI is exact here */
-      lo = t * ln2LO[0];
-    }
-    STRICT_ASSIGN(double, x, hi - lo);
-  } else if (hx < 0x3e300000) {         /* when |x|<2**-28 */
-    if (huge + x > one) return one + x; /* trigger inexact */
-  } else {
-    k = 0;
-  }
-
-  /* x is now in primary range */
-  t = x * x;
-  if (k >= -1021) {
-    INSERT_WORDS(twopk, 0x3ff00000 + (k << 20), 0);
-  } else {
-    INSERT_WORDS(twopk, 0x3ff00000 + ((k + 1000) << 20), 0);
-  }
-  c = x - t * (P1 + t * (P2 + t * (P3 + t * (P4 + t * P5))));
-  if (k == 0) {
-    return one - ((x * c) / (c - 2.0) - x);
-  } else {
-    y = one - ((lo - (x * c) / (2.0 - c)) - hi);
-  }
-  if (k >= -1021) {
-    if (k == 1024) return y * 2.0 * two1023;
-    return y * twopk;
-  } else {
-    return y * twopk * twom1000;
   }
 }