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authorgcc <gcc@7b3dc134-2b1b-0410-93df-9e9f96275f8d>2006-08-17 01:18:26 +0000
committergcc <gcc@7b3dc134-2b1b-0410-93df-9e9f96275f8d>2006-08-17 01:18:26 +0000
commit15f34685e7a9b5caf761af2ebf6afa20438d440b (patch)
treedc04ce3cdf040f198743c15b64557824de174680 /libc/sysdeps/ieee754/dbl-64/s_log1p.c
parent1e848e0e775a36f6359161f5deb890942ef42ff3 (diff)
downloadeglibc2-15f34685e7a9b5caf761af2ebf6afa20438d440b.tar.gz
Import glibc-mainline for 2006-08-16
git-svn-id: svn://svn.eglibc.org/fsf/trunk@4 7b3dc134-2b1b-0410-93df-9e9f96275f8d
Diffstat (limited to 'libc/sysdeps/ieee754/dbl-64/s_log1p.c')
-rw-r--r--libc/sysdeps/ieee754/dbl-64/s_log1p.c191
1 files changed, 191 insertions, 0 deletions
diff --git a/libc/sysdeps/ieee754/dbl-64/s_log1p.c b/libc/sysdeps/ieee754/dbl-64/s_log1p.c
new file mode 100644
index 000000000..0a9801a93
--- /dev/null
+++ b/libc/sysdeps/ieee754/dbl-64/s_log1p.c
@@ -0,0 +1,191 @@
+/* @(#)s_log1p.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ */
+/* Modified by Naohiko Shimizu/Tokai University, Japan 1997/08/25,
+ for performance improvement on pipelined processors.
+*/
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] = "$NetBSD: s_log1p.c,v 1.8 1995/05/10 20:47:46 jtc Exp $";
+#endif
+
+/* double log1p(double x)
+ *
+ * Method :
+ * 1. Argument Reduction: find k and f such that
+ * 1+x = 2^k * (1+f),
+ * where sqrt(2)/2 < 1+f < sqrt(2) .
+ *
+ * Note. If k=0, then f=x is exact. However, if k!=0, then f
+ * may not be representable exactly. In that case, a correction
+ * term is need. Let u=1+x rounded. Let c = (1+x)-u, then
+ * log(1+x) - log(u) ~ c/u. Thus, we proceed to compute log(u),
+ * and add back the correction term c/u.
+ * (Note: when x > 2**53, one can simply return log(x))
+ *
+ * 2. Approximation of log1p(f).
+ * Let s = f/(2+f) ; based on log(1+f) = log(1+s) - log(1-s)
+ * = 2s + 2/3 s**3 + 2/5 s**5 + .....,
+ * = 2s + s*R
+ * We use a special Reme algorithm on [0,0.1716] to generate
+ * a polynomial of degree 14 to approximate R The maximum error
+ * of this polynomial approximation is bounded by 2**-58.45. In
+ * other words,
+ * 2 4 6 8 10 12 14
+ * R(z) ~ Lp1*s +Lp2*s +Lp3*s +Lp4*s +Lp5*s +Lp6*s +Lp7*s
+ * (the values of Lp1 to Lp7 are listed in the program)
+ * and
+ * | 2 14 | -58.45
+ * | Lp1*s +...+Lp7*s - R(z) | <= 2
+ * | |
+ * Note that 2s = f - s*f = f - hfsq + s*hfsq, where hfsq = f*f/2.
+ * In order to guarantee error in log below 1ulp, we compute log
+ * by
+ * log1p(f) = f - (hfsq - s*(hfsq+R)).
+ *
+ * 3. Finally, log1p(x) = k*ln2 + log1p(f).
+ * = k*ln2_hi+(f-(hfsq-(s*(hfsq+R)+k*ln2_lo)))
+ * Here ln2 is split into two floating point number:
+ * ln2_hi + ln2_lo,
+ * where n*ln2_hi is always exact for |n| < 2000.
+ *
+ * Special cases:
+ * log1p(x) is NaN with signal if x < -1 (including -INF) ;
+ * log1p(+INF) is +INF; log1p(-1) is -INF with signal;
+ * log1p(NaN) is that NaN with no signal.
+ *
+ * Accuracy:
+ * according to an error analysis, the error is always less than
+ * 1 ulp (unit in the last place).
+ *
+ * Constants:
+ * The hexadecimal values are the intended ones for the following
+ * constants. The decimal values may be used, provided that the
+ * compiler will convert from decimal to binary accurately enough
+ * to produce the hexadecimal values shown.
+ *
+ * Note: Assuming log() return accurate answer, the following
+ * algorithm can be used to compute log1p(x) to within a few ULP:
+ *
+ * u = 1+x;
+ * if(u==1.0) return x ; else
+ * return log(u)*(x/(u-1.0));
+ *
+ * See HP-15C Advanced Functions Handbook, p.193.
+ */
+
+#include "math.h"
+#include "math_private.h"
+
+#ifdef __STDC__
+static const double
+#else
+static double
+#endif
+ln2_hi = 6.93147180369123816490e-01, /* 3fe62e42 fee00000 */
+ln2_lo = 1.90821492927058770002e-10, /* 3dea39ef 35793c76 */
+two54 = 1.80143985094819840000e+16, /* 43500000 00000000 */
+Lp[] = {0.0, 6.666666666666735130e-01, /* 3FE55555 55555593 */
+ 3.999999999940941908e-01, /* 3FD99999 9997FA04 */
+ 2.857142874366239149e-01, /* 3FD24924 94229359 */
+ 2.222219843214978396e-01, /* 3FCC71C5 1D8E78AF */
+ 1.818357216161805012e-01, /* 3FC74664 96CB03DE */
+ 1.531383769920937332e-01, /* 3FC39A09 D078C69F */
+ 1.479819860511658591e-01}; /* 3FC2F112 DF3E5244 */
+
+#ifdef __STDC__
+static const double zero = 0.0;
+#else
+static double zero = 0.0;
+#endif
+
+#ifdef __STDC__
+ double __log1p(double x)
+#else
+ double __log1p(x)
+ double x;
+#endif
+{
+ double hfsq,f,c,s,z,R,u,z2,z4,z6,R1,R2,R3,R4;
+ int32_t k,hx,hu,ax;
+
+ GET_HIGH_WORD(hx,x);
+ ax = hx&0x7fffffff;
+
+ k = 1;
+ if (hx < 0x3FDA827A) { /* x < 0.41422 */
+ if(ax>=0x3ff00000) { /* x <= -1.0 */
+ if(x==-1.0) return -two54/(x-x);/* log1p(-1)=+inf */
+ else return (x-x)/(x-x); /* log1p(x<-1)=NaN */
+ }
+ if(ax<0x3e200000) { /* |x| < 2**-29 */
+ if(two54+x>zero /* raise inexact */
+ &&ax<0x3c900000) /* |x| < 2**-54 */
+ return x;
+ else
+ return x - x*x*0.5;
+ }
+ if(hx>0||hx<=((int32_t)0xbfd2bec3)) {
+ k=0;f=x;hu=1;} /* -0.2929<x<0.41422 */
+ }
+ if (hx >= 0x7ff00000) return x+x;
+ if(k!=0) {
+ if(hx<0x43400000) {
+ u = 1.0+x;
+ GET_HIGH_WORD(hu,u);
+ k = (hu>>20)-1023;
+ c = (k>0)? 1.0-(u-x):x-(u-1.0);/* correction term */
+ c /= u;
+ } else {
+ u = x;
+ GET_HIGH_WORD(hu,u);
+ k = (hu>>20)-1023;
+ c = 0;
+ }
+ hu &= 0x000fffff;
+ if(hu<0x6a09e) {
+ SET_HIGH_WORD(u,hu|0x3ff00000); /* normalize u */
+ } else {
+ k += 1;
+ SET_HIGH_WORD(u,hu|0x3fe00000); /* normalize u/2 */
+ hu = (0x00100000-hu)>>2;
+ }
+ f = u-1.0;
+ }
+ hfsq=0.5*f*f;
+ if(hu==0) { /* |f| < 2**-20 */
+ if(f==zero) {
+ if(k==0) return zero;
+ else {c += k*ln2_lo; return k*ln2_hi+c;}
+ }
+ R = hfsq*(1.0-0.66666666666666666*f);
+ if(k==0) return f-R; else
+ return k*ln2_hi-((R-(k*ln2_lo+c))-f);
+ }
+ s = f/(2.0+f);
+ z = s*s;
+#ifdef DO_NOT_USE_THIS
+ R = z*(Lp1+z*(Lp2+z*(Lp3+z*(Lp4+z*(Lp5+z*(Lp6+z*Lp7))))));
+#else
+ R1 = z*Lp[1]; z2=z*z;
+ R2 = Lp[2]+z*Lp[3]; z4=z2*z2;
+ R3 = Lp[4]+z*Lp[5]; z6=z4*z2;
+ R4 = Lp[6]+z*Lp[7];
+ R = R1 + z2*R2 + z4*R3 + z6*R4;
+#endif
+ if(k==0) return f-(hfsq-s*(hfsq+R)); else
+ return k*ln2_hi-((hfsq-(s*(hfsq+R)+(k*ln2_lo+c)))-f);
+}
+weak_alias (__log1p, log1p)
+#ifdef NO_LONG_DOUBLE
+strong_alias (__log1p, __log1pl)
+weak_alias (__log1p, log1pl)
+#endif