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author | das <das@FreeBSD.org> | 2011-03-07 03:11:27 +0000 |
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committer | das <das@FreeBSD.org> | 2011-03-07 03:11:27 +0000 |
commit | c8691f6e6a0e57ecce0dc94678561826833214f4 (patch) | |
tree | 9b9903eb9f7f15c5406d5c4fd3327a96445326e8 /lib/msun | |
parent | 55e5832ebf71c5279994dae84bf74bc646ad717f (diff) | |
download | FreeBSD-src-c8691f6e6a0e57ecce0dc94678561826833214f4.zip FreeBSD-src-c8691f6e6a0e57ecce0dc94678561826833214f4.tar.gz |
Convert log10() to use __kernel_log(), which is more accurate and simpler.
Diffstat (limited to 'lib/msun')
-rw-r--r-- | lib/msun/src/e_log10.c | 54 |
1 files changed, 16 insertions, 38 deletions
diff --git a/lib/msun/src/e_log10.c b/lib/msun/src/e_log10.c index 7871b5e..135f0dc 100644 --- a/lib/msun/src/e_log10.c +++ b/lib/msun/src/e_log10.c @@ -14,45 +14,18 @@ #include <sys/cdefs.h> __FBSDID("$FreeBSD$"); -/* __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. +/* + * Return the base 10 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 */ -ivln10 = 4.34294481903251816668e-01, /* 0x3FDBCB7B, 0x1526E50E */ +ivln10hi = 4.34294481878168880939e-01, /* 0x3fdbcb7b, 0x15200000 */ +ivln10lo = 2.50829467116452752298e-11, /* 0x3dbb9438, 0xca9aadd5 */ log10_2hi = 3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */ log10_2lo = 3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */ @@ -61,7 +34,7 @@ static const double zero = 0.0; double __ieee754_log10(double x) { - double y,z; + double f,hi,lo,y,z; int32_t i,k,hx; u_int32_t lx; @@ -77,10 +50,15 @@ __ieee754_log10(double x) } if (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); - SET_HIGH_WORD(x,hx); - z = y*log10_2lo + ivln10*__ieee754_log(x); + hx &= 0x000fffff; + i = (hx+0x95f64)&0x100000; + SET_HIGH_WORD(x,hx|(i^0x3ff00000)); /* normalize x or x/2 */ + k += (i>>20); + y = (double)k; + f = __kernel_log(x); + hi = x = x - 1; + SET_LOW_WORD(hi,0); + lo = x - hi; + z = y*log10_2lo + (x+f)*ivln10lo + (lo+f)*ivln10hi + hi*ivln10hi; return z+y*log10_2hi; } |