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-rw-r--r--sysdeps/libm-ieee754/s_cbrtf.c118
1 files changed, 48 insertions, 70 deletions
diff --git a/sysdeps/libm-ieee754/s_cbrtf.c b/sysdeps/libm-ieee754/s_cbrtf.c
index a2b3c8106c..f9f687c011 100644
--- a/sysdeps/libm-ieee754/s_cbrtf.c
+++ b/sysdeps/libm-ieee754/s_cbrtf.c
@@ -1,84 +1,62 @@
-/* s_cbrtf.c -- float version of s_cbrt.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.
- * ====================================================
- */
-
-#if defined(LIBM_SCCS) && !defined(lint)
-static char rcsid[] = "$NetBSD: s_cbrtf.c,v 1.4 1995/05/10 20:46:51 jtc Exp $";
-#endif
+/* Compute cubic root of float value.
+ Copyright (C) 1997 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Dirk Alboth <dirka@uni-paderborn.de> and
+ Ulrich Drepper <drepper@cygnus.com>, 1997.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Library General Public License as
+ published by the Free Software Foundation; either version 2 of the
+ License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Library General Public License for more details.
+
+ You should have received a copy of the GNU Library General Public
+ License along with the GNU C Library; see the file COPYING.LIB. If not,
+ write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ Boston, MA 02111-1307, USA. */
#include "math.h"
#include "math_private.h"
-/* cbrtf(x)
- * Return cube root of x
- */
-#ifdef __STDC__
-static const unsigned
-#else
-static unsigned
-#endif
- B1 = 709958130, /* B1 = (84+2/3-0.03306235651)*2**23 */
- B2 = 642849266; /* B2 = (76+2/3-0.03306235651)*2**23 */
-#ifdef __STDC__
-static const float
-#else
-static float
-#endif
-C = 5.4285717010e-01, /* 19/35 = 0x3f0af8b0 */
-D = -7.0530611277e-01, /* -864/1225 = 0xbf348ef1 */
-E = 1.4142856598e+00, /* 99/70 = 0x3fb50750 */
-F = 1.6071428061e+00, /* 45/28 = 0x3fcdb6db */
-G = 3.5714286566e-01; /* 5/14 = 0x3eb6db6e */
+#define CBRT2 1.2599210498948731648 /* 2^(1/3) */
+#define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */
+
+static const double factor[5] =
+{
+ 1.0 / SQR_CBRT2,
+ 1.0 / CBRT2,
+ 1.0,
+ CBRT2,
+ SQR_CBRT2
+};
+
-#ifdef __STDC__
- float __cbrtf(float x)
-#else
- float __cbrtf(x)
- float x;
-#endif
+float
+__cbrtf (float x)
{
- float r,s,t;
- int32_t hx;
- u_int32_t sign;
- u_int32_t high;
+ float xm, ym, u, t2;
+ int xe;
+
+ /* Reduce X. XM now is an range 1.0 to 0.5. */
+ xm = __frexpf (fabsf (x), &xe);
- GET_FLOAT_WORD(hx,x);
- sign=hx&0x80000000; /* sign= sign(x) */
- hx ^=sign;
- if(hx>=0x7f800000) return(x+x); /* cbrt(NaN,INF) is itself */
- if(hx==0)
- return(x); /* cbrt(0) is itself */
+ /* If X is not finite or is null return it (with raising exceptions
+ if necessary. */
+ if (xe == 0)
+ return x + x;
- SET_FLOAT_WORD(x,hx); /* x <- |x| */
- /* rough cbrt to 5 bits */
- if(hx<0x00800000) /* subnormal number */
- {SET_FLOAT_WORD(t,0x4b800000); /* set t= 2**24 */
- t*=x; GET_FLOAT_WORD(high,t); SET_FLOAT_WORD(t,high/3+B2);
- }
- else
- SET_FLOAT_WORD(t,hx/3+B1);
+ u = (0.492659620528969547 + (0.697570460207922770
+ - 0.191502161678719066 * xm) * xm);
+ t2 = u * u * u;
- /* new cbrt to 23 bits */
- r=t*t/x;
- s=C+r*t;
- t*=G+F/(s+E+D/s);
+ ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3];
- /* retore the sign bit */
- GET_FLOAT_WORD(high,t);
- SET_FLOAT_WORD(t,high|sign);
- return(t);
+ return __ldexpf (x > 0.0 ? ym : -ym, xe / 3);
}
weak_alias (__cbrtf, cbrtf)