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-rw-r--r--libm/float/cbrtf.c119
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diff --git a/libm/float/cbrtf.c b/libm/float/cbrtf.c
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-/* cbrtf.c
- *
- * Cube root
- *
- *
- *
- * SYNOPSIS:
- *
- * float x, y, cbrtf();
- *
- * y = cbrtf( x );
- *
- *
- *
- * DESCRIPTION:
- *
- * Returns the cube root of the argument, which may be negative.
- *
- * Range reduction involves determining the power of 2 of
- * the argument. A polynomial of degree 2 applied to the
- * mantissa, and multiplication by the cube root of 1, 2, or 4
- * approximates the root to within about 0.1%. Then Newton's
- * iteration is used to converge to an accurate result.
- *
- *
- *
- * ACCURACY:
- *
- * Relative error:
- * arithmetic domain # trials peak rms
- * IEEE 0,1e38 100000 7.6e-8 2.7e-8
- *
- */
- /* cbrt.c */
-
-/*
-Cephes Math Library Release 2.2: June, 1992
-Copyright 1984, 1987, 1988, 1992 by Stephen L. Moshier
-Direct inquiries to 30 Frost Street, Cambridge, MA 02140
-*/
-
-
-#include <math.h>
-
-static float CBRT2 = 1.25992104989487316477;
-static float CBRT4 = 1.58740105196819947475;
-
-
-float frexpf(float, int *), ldexpf(float, int);
-
-float cbrtf( float xx )
-{
-int e, rem, sign;
-float x, z;
-
-x = xx;
-if( x == 0 )
- return( 0.0 );
-if( x > 0 )
- sign = 1;
-else
- {
- sign = -1;
- x = -x;
- }
-
-z = x;
-/* extract power of 2, leaving
- * mantissa between 0.5 and 1
- */
-x = frexpf( x, &e );
-
-/* Approximate cube root of number between .5 and 1,
- * peak relative error = 9.2e-6
- */
-x = (((-0.13466110473359520655053 * x
- + 0.54664601366395524503440 ) * x
- - 0.95438224771509446525043 ) * x
- + 1.1399983354717293273738 ) * x
- + 0.40238979564544752126924;
-
-/* exponent divided by 3 */
-if( e >= 0 )
- {
- rem = e;
- e /= 3;
- rem -= 3*e;
- if( rem == 1 )
- x *= CBRT2;
- else if( rem == 2 )
- x *= CBRT4;
- }
-
-
-/* argument less than 1 */
-
-else
- {
- e = -e;
- rem = e;
- e /= 3;
- rem -= 3*e;
- if( rem == 1 )
- x /= CBRT2;
- else if( rem == 2 )
- x /= CBRT4;
- e = -e;
- }
-
-/* multiply by power of 2 */
-x = ldexpf( x, e );
-
-/* Newton iteration */
-x -= ( x - (z/(x*x)) ) * 0.333333333333;
-
-if( sign < 0 )
- x = -x;
-return(x);
-}