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authorMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
committerMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
commit5f8de423f190bbb79a62f804151bc24824fa32d8 (patch)
tree10027f336435511475e392454359edea8e25895d /modules/fdlibm/src/e_log10.cpp
parent49ee0794b5d912db1f95dce6eb52d781dc210db5 (diff)
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Add m-esr52 at 52.6.0
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diff --git a/modules/fdlibm/src/e_log10.cpp b/modules/fdlibm/src/e_log10.cpp
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+
+/* @(#)e_log10.c 1.3 95/01/18 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunSoft, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+//#include <sys/cdefs.h>
+//__FBSDID("$FreeBSD$");
+
+/*
+ * Return the base 10 logarithm of x. See e_log.c and k_log.h for most
+ * comments.
+ *
+ * log10(x) = (f - 0.5*f*f + k_log1p(f)) / ln10 + k * log10(2)
+ * in not-quite-routine extra precision.
+ */
+
+#include <float.h>
+
+#include "math_private.h"
+#include "k_log.h"
+
+static const double
+two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
+ivln10hi = 4.34294481878168880939e-01, /* 0x3fdbcb7b, 0x15200000 */
+ivln10lo = 2.50829467116452752298e-11, /* 0x3dbb9438, 0xca9aadd5 */
+log10_2hi = 3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */
+log10_2lo = 3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */
+
+static const double zero = 0.0;
+static volatile double vzero = 0.0;
+
+double
+__ieee754_log10(double x)
+{
+ double f,hfsq,hi,lo,r,val_hi,val_lo,w,y,y2;
+ int32_t i,k,hx;
+ u_int32_t lx;
+
+ EXTRACT_WORDS(hx,lx,x);
+
+ k=0;
+ if (hx < 0x00100000) { /* x < 2**-1022 */
+ if (((hx&0x7fffffff)|lx)==0)
+ return -two54/vzero; /* log(+-0)=-inf */
+ if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
+ k -= 54; x *= two54; /* subnormal number, scale up x */
+ GET_HIGH_WORD(hx,x);
+ }
+ if (hx >= 0x7ff00000) return x+x;
+ if (hx == 0x3ff00000 && lx == 0)
+ return zero; /* log(1) = +0 */
+ k += (hx>>20)-1023;
+ hx &= 0x000fffff;
+ i = (hx+0x95f64)&0x100000;
+ SET_HIGH_WORD(x,hx|(i^0x3ff00000)); /* normalize x or x/2 */
+ k += (i>>20);
+ y = (double)k;
+ f = x - 1.0;
+ hfsq = 0.5*f*f;
+ r = k_log1p(f);
+
+ /* See e_log2.c for most details. */
+ hi = f - hfsq;
+ SET_LOW_WORD(hi,0);
+ lo = (f - hi) - hfsq + r;
+ val_hi = hi*ivln10hi;
+ y2 = y*log10_2hi;
+ val_lo = y*log10_2lo + (lo+hi)*ivln10lo + lo*ivln10hi;
+
+ /*
+ * Extra precision in for adding y*log10_2hi is not strictly needed
+ * since there is no very large cancellation near x = sqrt(2) or
+ * x = 1/sqrt(2), but we do it anyway since it costs little on CPUs
+ * with some parallelism and it reduces the error for many args.
+ */
+ w = y2 + val_hi;
+ val_lo += (y2 - w) + val_hi;
+ val_hi = w;
+
+ return val_lo + val_hi;
+}