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authorRich Felker <dalias@aerifal.cx>2011-02-12 00:22:29 -0500
committerRich Felker <dalias@aerifal.cx>2011-02-12 00:22:29 -0500
commit0b44a0315b47dd8eced9f3b7f31580cf14bbfc01 (patch)
tree6eaef0d8a720fa3da580de87b647fff796fe80b3 /src/math/s_expm1f.c
downloadmusl-0b44a0315b47dd8eced9f3b7f31580cf14bbfc01.tar.gz
initial check-in, version 0.5.0v0.5.0
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+/* s_expm1f.c -- float version of s_expm1.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,
+huge = 1.0e+30,
+tiny = 1.0e-30,
+o_threshold = 8.8721679688e+01,/* 0x42b17180 */
+ln2_hi = 6.9313812256e-01,/* 0x3f317180 */
+ln2_lo = 9.0580006145e-06,/* 0x3717f7d1 */
+invln2 = 1.4426950216e+00,/* 0x3fb8aa3b */
+ /* scaled coefficients related to expm1 */
+Q1 = -3.3333335072e-02, /* 0xbd088889 */
+Q2 = 1.5873016091e-03, /* 0x3ad00d01 */
+Q3 = -7.9365076090e-05, /* 0xb8a670cd */
+Q4 = 4.0082177293e-06, /* 0x36867e54 */
+Q5 = -2.0109921195e-07; /* 0xb457edbb */
+
+float
+expm1f(float x)
+{
+ float y,hi,lo,c=0.0,t,e,hxs,hfx,r1;
+ int32_t k,xsb;
+ uint32_t hx;
+
+ GET_FLOAT_WORD(hx,x);
+ xsb = hx&0x80000000; /* sign bit of x */
+ if(xsb==0) y=x; else y= -x; /* y = |x| */
+ hx &= 0x7fffffff; /* high word of |x| */
+
+ /* filter out huge and non-finite argument */
+ if(hx >= 0x4195b844) { /* if |x|>=27*ln2 */
+ if(hx >= 0x42b17218) { /* if |x|>=88.721... */
+ if(hx>0x7f800000)
+ return x+x; /* NaN */
+ if(hx==0x7f800000)
+ return (xsb==0)? x:-1.0;/* exp(+-inf)={inf,-1} */
+ if(x > o_threshold) return huge*huge; /* overflow */
+ }
+ if(xsb!=0) { /* x < -27*ln2, return -1.0 with inexact */
+ if(x+tiny<(float)0.0) /* raise inexact */
+ return tiny-one; /* return -1 */
+ }
+ }
+
+ /* argument reduction */
+ if(hx > 0x3eb17218) { /* if |x| > 0.5 ln2 */
+ if(hx < 0x3F851592) { /* 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)?(float)0.5:(float)-0.5);
+ t = k;
+ hi = x - t*ln2_hi; /* t*ln2_hi is exact here */
+ lo = t*ln2_lo;
+ }
+ x = hi - lo;
+ c = (hi-x)-lo;
+ }
+ else if(hx < 0x33000000) { /* when |x|<2**-25, return x */
+ t = huge+x; /* return x with inexact flags when x!=0 */
+ return x - (t-(huge+x));
+ }
+ else k = 0;
+
+ /* x is now in primary range */
+ hfx = (float)0.5*x;
+ hxs = x*hfx;
+ r1 = one+hxs*(Q1+hxs*(Q2+hxs*(Q3+hxs*(Q4+hxs*Q5))));
+ t = (float)3.0-r1*hfx;
+ e = hxs*((r1-t)/((float)6.0 - x*t));
+ if(k==0) return x - (x*e-hxs); /* c is 0 */
+ else {
+ e = (x*(e-c)-c);
+ e -= hxs;
+ if(k== -1) return (float)0.5*(x-e)-(float)0.5;
+ if(k==1) {
+ if(x < (float)-0.25) return -(float)2.0*(e-(x+(float)0.5));
+ else return one+(float)2.0*(x-e);
+ }
+ if (k <= -2 || k>56) { /* suffice to return exp(x)-1 */
+ int32_t i;
+ y = one-(e-x);
+ GET_FLOAT_WORD(i,y);
+ SET_FLOAT_WORD(y,i+(k<<23)); /* add k to y's exponent */
+ return y-one;
+ }
+ t = one;
+ if(k<23) {
+ int32_t i;
+ SET_FLOAT_WORD(t,0x3f800000 - (0x1000000>>k)); /* t=1-2^-k */
+ y = t-(e-x);
+ GET_FLOAT_WORD(i,y);
+ SET_FLOAT_WORD(y,i+(k<<23)); /* add k to y's exponent */
+ } else {
+ int32_t i;
+ SET_FLOAT_WORD(t,((0x7f-k)<<23)); /* 2^-k */
+ y = x-(e+t);
+ y += one;
+ GET_FLOAT_WORD(i,y);
+ SET_FLOAT_WORD(y,i+(k<<23)); /* add k to y's exponent */
+ }
+ }
+ return y;
+}