From 0b44a0315b47dd8eced9f3b7f31580cf14bbfc01 Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Sat, 12 Feb 2011 00:22:29 -0500
Subject: initial check-in, version 0.5.0

---
 src/math/e_expf.c | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 src/math/e_expf.c

(limited to 'src/math/e_expf.c')

diff --git a/src/math/e_expf.c b/src/math/e_expf.c
new file mode 100644
index 00000000..99818edc
--- /dev/null
+++ b/src/math/e_expf.c
@@ -0,0 +1,91 @@
+/* e_expf.c -- float version of e_exp.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 <math.h>
+#include "math_private.h"
+
+static const float
+one     = 1.0,
+halF[2] = {0.5,-0.5,},
+huge    = 1.0e+30,
+twom100 = 7.8886090522e-31,      /* 2**-100=0x0d800000 */
+o_threshold=  8.8721679688e+01,  /* 0x42b17180 */
+u_threshold= -1.0397208405e+02,  /* 0xc2cff1b5 */
+ln2HI[2]   ={ 6.9313812256e-01,         /* 0x3f317180 */
+             -6.9313812256e-01,},       /* 0xbf317180 */
+ln2LO[2]   ={ 9.0580006145e-06,         /* 0x3717f7d1 */
+             -9.0580006145e-06,},       /* 0xb717f7d1 */
+invln2 =  1.4426950216e+00,             /* 0x3fb8aa3b */
+P1   =  1.6666667163e-01, /* 0x3e2aaaab */
+P2   = -2.7777778450e-03, /* 0xbb360b61 */
+P3   =  6.6137559770e-05, /* 0x388ab355 */
+P4   = -1.6533901999e-06, /* 0xb5ddea0e */
+P5   =  4.1381369442e-08; /* 0x3331bb4c */
+
+float
+expf(float x) /* default IEEE double exp */
+{
+        float y,hi=0.0,lo=0.0,c,t;
+        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)
+                 return x+x;                    /* NaN */
+            if(hx==0x7f800000)
+                return (xsb==0)? x:0.0;         /* exp(+-inf)={inf,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];
+            }
+            x  = hi - lo;
+        }
+        else if(hx < 0x31800000)  {     /* 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;
+        c  = x - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
+        if(k==0)        return one-((x*c)/(c-(float)2.0)-x);
+        else            y = one-((lo-(x*c)/((float)2.0-c))-hi);
+        if(k >= -125) {
+            uint32_t hy;
+            GET_FLOAT_WORD(hy,y);
+            SET_FLOAT_WORD(y,hy+(k<<23));       /* add k to y's exponent */
+            return y;
+        } else {
+            uint32_t hy;
+            GET_FLOAT_WORD(hy,y);
+            SET_FLOAT_WORD(y,hy+((k+100)<<23)); /* add k to y's exponent */
+            return y*twom100;
+        }
+}
-- 
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