first commit of the new libm!

[musl] / src / math / expf.c

diff --git a/src/math/expf.c b/src/math/expf.c
new file mode 100644 (file)
index 0000000..a0eaa7a
--- /dev/null
+++ b/src/math/expf.c
@@ -0,0 +1,95 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/e_expf.c */
+/*
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#include "libm.h"
+
+static const float
+one     = 1.0,
+halF[2] = {0.5,-0.5,},
+huge    = 1.0e+30,
+o_threshold =  8.8721679688e+01,  /* 0x42b17180 */
+u_threshold = -1.0397208405e+02,  /* 0xc2cff1b5 */
+ln2HI[2]   = { 6.9314575195e-01,  /* 0x3f317200 */
+              -6.9314575195e-01,},/* 0xbf317200 */
+ln2LO[2]   = { 1.4286067653e-06,  /* 0x35bfbe8e */
+              -1.4286067653e-06,},/* 0xb5bfbe8e */
+invln2 = 1.4426950216e+00,        /* 0x3fb8aa3b */
+/*
+ * Domain [-0.34568, 0.34568], range ~[-4.278e-9, 4.447e-9]:
+ * |x*(exp(x)+1)/(exp(x)-1) - p(x)| < 2**-27.74
+ */
+P1 =  1.6666625440e-1, /*  0xaaaa8f.0p-26 */
+P2 = -2.7667332906e-3; /* -0xb55215.0p-32 */
+
+static volatile float twom100 = 7.8886090522e-31; /* 2**-100=0x0d800000 */
+
+float expf(float x)
+{
+       float y,hi=0.0,lo=0.0,c,t,twopk;
+       int32_t k=0,xsb;
+       uint32_t hx;
+
+       GET_FLOAT_WORD(hx, x);
+       xsb = (hx>>31)&1;  /* sign bit of x */
+       hx &= 0x7fffffff;  /* high word of |x| */
+
+       /* filter out non-finite argument */
+       if (hx >= 0x42b17218) {  /* if |x|>=88.721... */
+               if (hx > 0x7f800000)  /* NaN */
+                       return x+x;
+               if (hx == 0x7f800000)  /* exp(+-inf)={inf,0} */
+                       return xsb==0 ? x : 0.0;
+               if (x > o_threshold)
+                       return huge*huge; /* overflow */
+               if (x < u_threshold)
+                       return twom100*twom100; /* underflow */
+       }
+
+       /* argument reduction */
+       if (hx > 0x3eb17218) {  /* if  |x| > 0.5 ln2 */
+               if (hx < 0x3F851592) {  /* and |x| < 1.5 ln2 */
+                       hi = x-ln2HI[xsb];
+                       lo = ln2LO[xsb];
+                       k = 1 - xsb - xsb;
+               } else {
+                       k  = invln2*x + halF[xsb];
+                       t  = k;
+                       hi = x - t*ln2HI[0];  /* t*ln2HI is exact here */
+                       lo = t*ln2LO[0];
+               }
+               STRICT_ASSIGN(float, x, hi - lo);
+       } else if(hx < 0x39000000)  {  /* |x|<2**-14 */
+               /* raise inexact */
+               if (huge+x > one)
+                       return one + x;
+       } else
+               k = 0;
+
+       /* x is now in primary range */
+       t = x*x;
+       if (k >= -125)
+               SET_FLOAT_WORD(twopk, 0x3f800000+(k<<23));
+       else
+               SET_FLOAT_WORD(twopk, 0x3f800000+((k+100)<<23));
+       c  = x - t*(P1+t*P2);
+       if (k == 0)
+               return one - ((x*c)/(c-(float)2.0)-x);
+       y = one - ((lo-(x*c)/((float)2.0-c))-hi);
+       if (k < -125)
+               return y*twopk*twom100;
+       if (k == 128)
+               return y*2.0F*0x1p127F;
+       return y*twopk;
+}