diff options
Diffstat (limited to 'lib/mlibc/options/ansi/musl-generic-math/log2.c')
| -rw-r--r-- | lib/mlibc/options/ansi/musl-generic-math/log2.c | 122 |
1 files changed, 0 insertions, 122 deletions
diff --git a/lib/mlibc/options/ansi/musl-generic-math/log2.c b/lib/mlibc/options/ansi/musl-generic-math/log2.c deleted file mode 100644 index 0aafad4..0000000 --- a/lib/mlibc/options/ansi/musl-generic-math/log2.c +++ /dev/null @@ -1,122 +0,0 @@ -/* origin: FreeBSD /usr/src/lib/msun/src/e_log2.c */ -/* - * ==================================================== - * 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. - * ==================================================== - */ -/* - * Return the base 2 logarithm of x. See log.c for most comments. - * - * Reduce x to 2^k (1+f) and calculate r = log(1+f) - f + f*f/2 - * as in log.c, then combine and scale in extra precision: - * log2(x) = (f - f*f/2 + r)/log(2) + k - */ - -#include <math.h> -#include <stdint.h> - -static const double -ivln2hi = 1.44269504072144627571e+00, /* 0x3ff71547, 0x65200000 */ -ivln2lo = 1.67517131648865118353e-10, /* 0x3de705fc, 0x2eefa200 */ -Lg1 = 6.666666666666735130e-01, /* 3FE55555 55555593 */ -Lg2 = 3.999999999940941908e-01, /* 3FD99999 9997FA04 */ -Lg3 = 2.857142874366239149e-01, /* 3FD24924 94229359 */ -Lg4 = 2.222219843214978396e-01, /* 3FCC71C5 1D8E78AF */ -Lg5 = 1.818357216161805012e-01, /* 3FC74664 96CB03DE */ -Lg6 = 1.531383769920937332e-01, /* 3FC39A09 D078C69F */ -Lg7 = 1.479819860511658591e-01; /* 3FC2F112 DF3E5244 */ - -double log2(double x) -{ - union {double f; uint64_t i;} u = {x}; - double_t hfsq,f,s,z,R,w,t1,t2,y,hi,lo,val_hi,val_lo; - uint32_t hx; - int k; - - hx = u.i>>32; - k = 0; - if (hx < 0x00100000 || hx>>31) { - if (u.i<<1 == 0) - return -1/(x*x); /* log(+-0)=-inf */ - if (hx>>31) - return (x-x)/0.0; /* log(-#) = NaN */ - /* subnormal number, scale x up */ - k -= 54; - x *= 0x1p54; - u.f = x; - hx = u.i>>32; - } else if (hx >= 0x7ff00000) { - return x; - } else if (hx == 0x3ff00000 && u.i<<32 == 0) - return 0; - - /* reduce x into [sqrt(2)/2, sqrt(2)] */ - hx += 0x3ff00000 - 0x3fe6a09e; - k += (int)(hx>>20) - 0x3ff; - hx = (hx&0x000fffff) + 0x3fe6a09e; - u.i = (uint64_t)hx<<32 | (u.i&0xffffffff); - x = u.f; - - f = x - 1.0; - hfsq = 0.5*f*f; - s = f/(2.0+f); - z = s*s; - w = z*z; - t1 = w*(Lg2+w*(Lg4+w*Lg6)); - t2 = z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7))); - R = t2 + t1; - - /* - * f-hfsq must (for args near 1) be evaluated in extra precision - * to avoid a large cancellation when x is near sqrt(2) or 1/sqrt(2). - * This is fairly efficient since f-hfsq only depends on f, so can - * be evaluated in parallel with R. Not combining hfsq with R also - * keeps R small (though not as small as a true `lo' term would be), - * so that extra precision is not needed for terms involving R. - * - * Compiler bugs involving extra precision used to break Dekker's - * theorem for spitting f-hfsq as hi+lo, unless double_t was used - * or the multi-precision calculations were avoided when double_t - * has extra precision. These problems are now automatically - * avoided as a side effect of the optimization of combining the - * Dekker splitting step with the clear-low-bits step. - * - * y must (for args near sqrt(2) and 1/sqrt(2)) be added in extra - * precision to avoid a very large cancellation when x is very near - * these values. Unlike the above cancellations, this problem is - * specific to base 2. It is strange that adding +-1 is so much - * harder than adding +-ln2 or +-log10_2. - * - * This uses Dekker's theorem to normalize y+val_hi, so the - * compiler bugs are back in some configurations, sigh. And I - * don't want to used double_t to avoid them, since that gives a - * pessimization and the support for avoiding the pessimization - * is not yet available. - * - * The multi-precision calculations for the multiplications are - * routine. - */ - - /* hi+lo = f - hfsq + s*(hfsq+R) ~ log(1+f) */ - hi = f - hfsq; - u.f = hi; - u.i &= (uint64_t)-1<<32; - hi = u.f; - lo = f - hi - hfsq + s*(hfsq+R); - - val_hi = hi*ivln2hi; - val_lo = (lo+hi)*ivln2lo + lo*ivln2hi; - - /* spadd(val_hi, val_lo, y), except for not using double_t: */ - y = k; - w = y + val_hi; - val_lo += (y - w) + val_hi; - val_hi = w; - - return val_lo + val_hi; -} |