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Diffstat (limited to 'lib/msun/src/e_log2.c')
-rw-r--r-- | lib/msun/src/e_log2.c | 60 |
1 files changed, 60 insertions, 0 deletions
diff --git a/lib/msun/src/e_log2.c b/lib/msun/src/e_log2.c new file mode 100644 index 0000000..6cf3dbc --- /dev/null +++ b/lib/msun/src/e_log2.c @@ -0,0 +1,60 @@ + +/* @(#)e_log10.c 1.3 95/01/18 */ +/* + * ==================================================== + * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. + * + * Developed at SunSoft, a Sun Microsystems, Inc. business. + * Permission to use, copy, modify, and distribute this + * software is freely granted, provided that this notice + * is preserved. + * ==================================================== + */ + +#include <sys/cdefs.h> +__FBSDID("$FreeBSD$"); + +/* + * Return the base 2 logarithm of x. See k_log.c for details on the algorithm. + */ + +#include "math.h" +#include "math_private.h" +#include "k_log.h" + +static const double +two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ +ivln2hi = 1.44269504072144627571e+00, /* 0x3ff71547, 0x65200000 */ +ivln2lo = 1.67517131648865118353e-10; /* 0x3de705fc, 0x2eefa200 */ + +static const double zero = 0.0; + +double +__ieee754_log2(double x) +{ + double f,hi,lo; + int32_t i,k,hx; + u_int32_t lx; + + EXTRACT_WORDS(hx,lx,x); + + k=0; + if (hx < 0x00100000) { /* x < 2**-1022 */ + if (((hx&0x7fffffff)|lx)==0) + return -two54/zero; /* log(+-0)=-inf */ + if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ + k -= 54; x *= two54; /* subnormal number, scale up x */ + GET_HIGH_WORD(hx,x); + } + if (hx >= 0x7ff00000) return x+x; + k += (hx>>20)-1023; + hx &= 0x000fffff; + i = (hx+0x95f64)&0x100000; + SET_HIGH_WORD(x,hx|(i^0x3ff00000)); /* normalize x or x/2 */ + k += (i>>20); + f = __kernel_log(x); + hi = x = x - 1; + SET_LOW_WORD(hi,0); + lo = x - hi; + return (x+f)*ivln2lo + (lo+f)*ivln2hi + hi*ivln2hi + k; +} |