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Diffstat (limited to 'REORG.TODO/sysdeps/ieee754/dbl-64/e_log10.c')
| -rw-r--r-- | REORG.TODO/sysdeps/ieee754/dbl-64/e_log10.c | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/ieee754/dbl-64/e_log10.c b/REORG.TODO/sysdeps/ieee754/dbl-64/e_log10.c new file mode 100644 index 0000000000..bf40bca874 --- /dev/null +++ b/REORG.TODO/sysdeps/ieee754/dbl-64/e_log10.c @@ -0,0 +1,88 @@ +/* @(#)e_log10.c 5.1 93/09/24 */ +/* + * ==================================================== + * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. + * + * Developed at SunPro, a Sun Microsystems, Inc. business. + * Permission to use, copy, modify, and distribute this + * software is freely granted, provided that this notice + * is preserved. + * ==================================================== + */ + +/* __ieee754_log10(x) + * Return the base 10 logarithm of x + * + * Method : + * Let log10_2hi = leading 40 bits of log10(2) and + * log10_2lo = log10(2) - log10_2hi, + * ivln10 = 1/log(10) rounded. + * Then + * n = ilogb(x), + * if(n<0) n = n+1; + * x = scalbn(x,-n); + * log10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x)) + * + * Note 1: + * To guarantee log10(10**n)=n, where 10**n is normal, the rounding + * mode must set to Round-to-Nearest. + * Note 2: + * [1/log(10)] rounded to 53 bits has error .198 ulps; + * log10 is monotonic at all binary break points. + * + * Special cases: + * log10(x) is NaN with signal if x < 0; + * log10(+INF) is +INF with no signal; log10(0) is -INF with signal; + * log10(NaN) is that NaN with no signal; + * log10(10**N) = N for N=0,1,...,22. + * + * 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 <math_private.h> +#include <fix-int-fp-convert-zero.h> + +static const double two54 = 1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */ +static const double ivln10 = 4.34294481903251816668e-01; /* 0x3FDBCB7B, 0x1526E50E */ +static const double log10_2hi = 3.01029995663611771306e-01; /* 0x3FD34413, 0x509F6000 */ +static const double log10_2lo = 3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */ + +double +__ieee754_log10 (double x) +{ + double y, z; + int32_t i, k, hx; + u_int32_t lx; + + EXTRACT_WORDS (hx, lx, x); + + k = 0; + if (hx < 0x00100000) + { /* x < 2**-1022 */ + if (__glibc_unlikely (((hx & 0x7fffffff) | lx) == 0)) + return -two54 / __fabs (x); /* log(+-0)=-inf */ + if (__glibc_unlikely (hx < 0)) + return (x - x) / (x - x); /* log(-#) = NaN */ + k -= 54; + x *= two54; /* subnormal number, scale up x */ + GET_HIGH_WORD (hx, x); + } + if (__glibc_unlikely (hx >= 0x7ff00000)) + return x + x; + k += (hx >> 20) - 1023; + i = ((u_int32_t) k & 0x80000000) >> 31; + hx = (hx & 0x000fffff) | ((0x3ff - i) << 20); + y = (double) (k + i); + if (FIX_INT_FP_CONVERT_ZERO && y == 0.0) + y = 0.0; + SET_HIGH_WORD (x, hx); + z = y * log10_2lo + ivln10 * __ieee754_log (x); + return z + y * log10_2hi; +} + +strong_alias (__ieee754_log10, __log10_finite) |