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Diffstat (limited to 'libm/float/log2f.c')
-rw-r--r-- | libm/float/log2f.c | 129 |
1 files changed, 0 insertions, 129 deletions
diff --git a/libm/float/log2f.c b/libm/float/log2f.c deleted file mode 100644 index 5cd5f4838..000000000 --- a/libm/float/log2f.c +++ /dev/null @@ -1,129 +0,0 @@ -/* log2f.c - * - * Base 2 logarithm - * - * - * - * SYNOPSIS: - * - * float x, y, log2f(); - * - * y = log2f( x ); - * - * - * - * DESCRIPTION: - * - * Returns the base 2 logarithm of x. - * - * The argument is separated into its exponent and fractional - * parts. If the exponent is between -1 and +1, the base e - * logarithm of the fraction is approximated by - * - * log(1+x) = x - 0.5 x**2 + x**3 P(x)/Q(x). - * - * Otherwise, setting z = 2(x-1)/x+1), - * - * log(x) = z + z**3 P(z)/Q(z). - * - * - * - * ACCURACY: - * - * Relative error: - * arithmetic domain # trials peak rms - * IEEE exp(+-88) 100000 1.1e-7 2.4e-8 - * IEEE 0.5, 2.0 100000 1.1e-7 3.0e-8 - * - * In the tests over the interval [exp(+-88)], the logarithms - * of the random arguments were uniformly distributed. - * - * ERROR MESSAGES: - * - * log singularity: x = 0; returns MINLOGF/log(2) - * log domain: x < 0; returns MINLOGF/log(2) - */ - -/* -Cephes Math Library Release 2.2: June, 1992 -Copyright 1984, 1992 by Stephen L. Moshier -Direct inquiries to 30 Frost Street, Cambridge, MA 02140 -*/ - -#include <math.h> -static char fname[] = {"log2"}; - -/* Coefficients for log(1+x) = x - x**2/2 + x**3 P(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 LOG2EA 0.44269504088896340735992 -#define SQRTH 0.70710678118654752440 -extern float MINLOGF, LOGE2F; - -float frexpf(float, int *), polevlf(float, float *, int); - -float log2f(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( MINLOGF/LOGE2F ); - } - -/* separate mantissa from exponent */ -x = frexpf( x, &e ); - - -/* logarithm using log(1+x) = x - .5x**2 + x**3 P(x)/Q(x) */ - -if( x < SQRTH ) - { - e -= 1; - x = 2.0*x - 1.0; - } -else - { - x = x - 1.0; - } - -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 log2(e) - * and base 2 exponent by 1 - * - * ***CAUTION*** - * - * This sequence of operations is critical and it may - * be horribly defeated by some compiler optimizers. - */ -z = y * LOG2EA; -z += x * LOG2EA; -z += y; -z += x; -z += (float )e; -return( z ); -} |