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-rw-r--r--src/math/e_logf.c81
1 files changed, 81 insertions, 0 deletions
diff --git a/src/math/e_logf.c b/src/math/e_logf.c
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+/* e_logf.c -- float version of e_log.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
+ln2_hi = 6.9313812256e-01, /* 0x3f317180 */
+ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */
+two25 = 3.355443200e+07, /* 0x4c000000 */
+Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
+Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
+Lg3 = 2.8571429849e-01, /* 3E924925 */
+Lg4 = 2.2222198546e-01, /* 3E638E29 */
+Lg5 = 1.8183572590e-01, /* 3E3A3325 */
+Lg6 = 1.5313838422e-01, /* 3E1CD04F */
+Lg7 = 1.4798198640e-01; /* 3E178897 */
+
+static const float zero = 0.0;
+
+float
+logf(float x)
+{
+ float hfsq,f,s,z,R,w,t1,t2,dk;
+ int32_t k,ix,i,j;
+
+ GET_FLOAT_WORD(ix,x);
+
+ k=0;
+ if (ix < 0x00800000) { /* x < 2**-126 */
+ if ((ix&0x7fffffff)==0)
+ return -two25/zero; /* log(+-0)=-inf */
+ if (ix<0) return (x-x)/zero; /* log(-#) = NaN */
+ k -= 25; x *= two25; /* subnormal number, scale up x */
+ GET_FLOAT_WORD(ix,x);
+ }
+ if (ix >= 0x7f800000) return x+x;
+ k += (ix>>23)-127;
+ ix &= 0x007fffff;
+ i = (ix+(0x95f64<<3))&0x800000;
+ SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */
+ k += (i>>23);
+ f = x-(float)1.0;
+ if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */
+ if(f==zero) { if(k==0) return zero; else {dk=(float)k;
+ return dk*ln2_hi+dk*ln2_lo;} }
+ R = f*f*((float)0.5-(float)0.33333333333333333*f);
+ if(k==0) return f-R; else {dk=(float)k;
+ return dk*ln2_hi-((R-dk*ln2_lo)-f);}
+ }
+ s = f/((float)2.0+f);
+ dk = (float)k;
+ z = s*s;
+ i = ix-(0x6147a<<3);
+ w = z*z;
+ j = (0x6b851<<3)-ix;
+ t1= w*(Lg2+w*(Lg4+w*Lg6));
+ t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
+ i |= j;
+ R = t2+t1;
+ if(i>0) {
+ hfsq=(float)0.5*f*f;
+ if(k==0) return f-(hfsq-s*(hfsq+R)); else
+ return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
+ } else {
+ if(k==0) return f-s*(f-R); else
+ return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
+ }
+}