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Diffstat (limited to 'lib/mlibc/options/ansi/musl-generic-math/log.c')
| -rw-r--r-- | lib/mlibc/options/ansi/musl-generic-math/log.c | 118 |
1 files changed, 0 insertions, 118 deletions
diff --git a/lib/mlibc/options/ansi/musl-generic-math/log.c b/lib/mlibc/options/ansi/musl-generic-math/log.c deleted file mode 100644 index e61e113..0000000 --- a/lib/mlibc/options/ansi/musl-generic-math/log.c +++ /dev/null @@ -1,118 +0,0 @@ -/* origin: FreeBSD /usr/src/lib/msun/src/e_log.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. - * ==================================================== - */ -/* log(x) - * Return the logarithm of x - * - * Method : - * 1. Argument Reduction: find k and f such that - * x = 2^k * (1+f), - * where sqrt(2)/2 < 1+f < sqrt(2) . - * - * 2. Approximation of log(1+f). - * Let s = f/(2+f) ; based on log(1+f) = log(1+s) - log(1-s) - * = 2s + 2/3 s**3 + 2/5 s**5 + ....., - * = 2s + s*R - * We use a special Remez algorithm on [0,0.1716] to generate - * a polynomial of degree 14 to approximate R The maximum error - * of this polynomial approximation is bounded by 2**-58.45. In - * other words, - * 2 4 6 8 10 12 14 - * R(z) ~ Lg1*s +Lg2*s +Lg3*s +Lg4*s +Lg5*s +Lg6*s +Lg7*s - * (the values of Lg1 to Lg7 are listed in the program) - * and - * | 2 14 | -58.45 - * | Lg1*s +...+Lg7*s - R(z) | <= 2 - * | | - * Note that 2s = f - s*f = f - hfsq + s*hfsq, where hfsq = f*f/2. - * In order to guarantee error in log below 1ulp, we compute log - * by - * log(1+f) = f - s*(f - R) (if f is not too large) - * log(1+f) = f - (hfsq - s*(hfsq+R)). (better accuracy) - * - * 3. Finally, log(x) = k*ln2 + log(1+f). - * = k*ln2_hi+(f-(hfsq-(s*(hfsq+R)+k*ln2_lo))) - * Here ln2 is split into two floating point number: - * ln2_hi + ln2_lo, - * where n*ln2_hi is always exact for |n| < 2000. - * - * Special cases: - * log(x) is NaN with signal if x < 0 (including -INF) ; - * log(+INF) is +INF; log(0) is -INF with signal; - * log(NaN) is that NaN with no signal. - * - * Accuracy: - * according to an error analysis, the error is always less than - * 1 ulp (unit in the last place). - * - * Constants: - * The hexadecimal values are the intended ones for the following - * constants. The decimal values may be used, provided that the - * compiler will convert from decimal to binary accurately enough - * to produce the hexadecimal values shown. - */ - -#include <math.h> -#include <stdint.h> - -static const double -ln2_hi = 6.93147180369123816490e-01, /* 3fe62e42 fee00000 */ -ln2_lo = 1.90821492927058770002e-10, /* 3dea39ef 35793c76 */ -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 log(double x) -{ - union {double f; uint64_t i;} u = {x}; - double_t hfsq,f,s,z,R,w,t1,t2,dk; - 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; - dk = k; - return s*(hfsq+R) + dk*ln2_lo - hfsq + f + dk*ln2_hi; -} |