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-rw-r--r--libm/float/log10f.c129
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diff --git a/libm/float/log10f.c b/libm/float/log10f.c
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-/* log10f.c
- *
- * Common logarithm
- *
- *
- *
- * SYNOPSIS:
- *
- * float x, y, log10f();
- *
- * y = log10f( x );
- *
- *
- *
- * DESCRIPTION:
- *
- * Returns logarithm to the base 10 of x.
- *
- * The argument is separated into its exponent and fractional
- * parts. The logarithm of the fraction is approximated by
- *
- * log(1+x) = x - 0.5 x**2 + x**3 P(x).
- *
- *
- *
- * ACCURACY:
- *
- * Relative error:
- * arithmetic domain # trials peak rms
- * IEEE 0.5, 2.0 100000 1.3e-7 3.4e-8
- * IEEE 0, MAXNUMF 100000 1.3e-7 2.6e-8
- *
- * In the tests over the interval [0, MAXNUM], the logarithms
- * of the random arguments were uniformly distributed over
- * [-MAXL10, MAXL10].
- *
- * ERROR MESSAGES:
- *
- * log10f singularity: x = 0; returns -MAXL10
- * log10f domain: x < 0; returns -MAXL10
- * MAXL10 = 38.230809449325611792
- */
-
-/*
-Cephes Math Library Release 2.1: December, 1988
-Copyright 1984, 1987, 1988 by Stephen L. Moshier
-Direct inquiries to 30 Frost Street, Cambridge, MA 02140
-*/
-
-#include <math.h>
-static char fname[] = {"log10"};
-
-/* Coefficients for log(1+x) = x - x**2/2 + x**3 P(x)/Q(x)
- * 1/sqrt(2) <= x < sqrt(2)
- */
-static float P[] = {
- 7.0376836292E-2,
--1.1514610310E-1,
- 1.1676998740E-1,
--1.2420140846E-1,
- 1.4249322787E-1,
--1.6668057665E-1,
- 2.0000714765E-1,
--2.4999993993E-1,
- 3.3333331174E-1
-};
-
-
-#define SQRTH 0.70710678118654752440
-#define L102A 3.0078125E-1
-#define L102B 2.48745663981195213739E-4
-#define L10EA 4.3359375E-1
-#define L10EB 7.00731903251827651129E-4
-
-static float MAXL10 = 38.230809449325611792;
-
-float frexpf(float, int *), polevlf(float, float *, int);
-
-float log10f(float xx)
-{
-float x, y, z;
-int e;
-
-x = xx;
-/* Test for domain */
-if( x <= 0.0 )
- {
- if( x == 0.0 )
- mtherr( fname, SING );
- else
- mtherr( fname, DOMAIN );
- return( -MAXL10 );
- }
-
-/* separate mantissa from exponent */
-
-x = frexpf( x, &e );
-
-/* logarithm using log(1+x) = x - .5x**2 + x**3 P(x) */
-
-if( x < SQRTH )
- {
- e -= 1;
- x = 2.0*x - 1.0;
- }
-else
- {
- x = x - 1.0;
- }
-
-
-/* rational form */
-z = x*x;
-y = x * ( z * polevlf( x, P, 8 ) );
-y = y - 0.5 * z; /* y - 0.5 * x**2 */
-
-/* multiply log of fraction by log10(e)
- * and base 2 exponent by log10(2)
- */
-z = (x + y) * L10EB; /* accumulate terms in order of size */
-z += y * L10EA;
-z += x * L10EA;
-x = e;
-z += x * L102B;
-z += x * L102A;
-
-
-return( z );
-}