Revert r241756

lib/msun/src/e_expf.c

@@ -21,68 +21,6 @@ __FBSDID("$FreeBSD$");
 #include "math.h"
 #include "math_private.h"
 
-/* __ieee754_expf
- * 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 2 to approximate R. The maximum error 
- *      of this polynomial approximation is bounded by 2**-27. In
- *      other words,
- *          R(z) ~ 2.0 + P1*z + P2*z*z
- *      (where z=r*r, and the values of P1 and P2 are listed below)
- *      and
- *          |              2          |     -27
- *          | 2.0+P1*z+P2*z   -  R(z) | <= 2 
- *          |                         |
- *      The computation of expf(r) thus becomes
- *                             2*r
- *             expf(r) = 1 + -------
- *                            R - r
- *                                 r*R1(r)
- *                     = 1 + r + ----------- (for better accuracy)
- *                                2 - R1(r)
- *      where
- *                               2       4
- *              R1(r) = r - (P1*r  + P2*r)
- *      
- *   3. Scale back to obtain expf(x):
- *      From step 1, we have
- *         expf(x) = 2^k * expf(r)
- *
- * Special cases:
- *      expf(INF) is INF, exp(NaN) is NaN;
- *      expf(-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
- *      0.5013 ulp (unit in the last place).
- *
- * Misc. info.
- *      For IEEE float
- *          if x >  8.8721679688e+01 then exp(x) overflow
- *          if x < -1.0397208405e+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.
- */
 static const float
 one	= 1.0,
 halF[2]	= {0.5,-0.5,},