1141296Sdas 2141296Sdas/* @(#)e_log10.c 1.3 95/01/18 */ 32116Sjkh/* 42116Sjkh * ==================================================== 52116Sjkh * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 62116Sjkh * 7141296Sdas * Developed at SunSoft, a Sun Microsystems, Inc. business. 82116Sjkh * Permission to use, copy, modify, and distribute this 9141296Sdas * software is freely granted, provided that this notice 102116Sjkh * is preserved. 112116Sjkh * ==================================================== 122116Sjkh */ 132116Sjkh 14176451Sdas#include <sys/cdefs.h> 15176451Sdas__FBSDID("$FreeBSD$"); 162116Sjkh 17219360Sdas/* 18219360Sdas * Return the base 10 logarithm of x. See k_log.c for details on the algorithm. 192116Sjkh */ 202116Sjkh 212116Sjkh#include "math.h" 222116Sjkh#include "math_private.h" 23219360Sdas#include "k_log.h" 242116Sjkh 252116Sjkhstatic const double 262116Sjkhtwo54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 27219360Sdasivln10hi = 4.34294481878168880939e-01, /* 0x3fdbcb7b, 0x15200000 */ 28219360Sdasivln10lo = 2.50829467116452752298e-11, /* 0x3dbb9438, 0xca9aadd5 */ 292116Sjkhlog10_2hi = 3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */ 302116Sjkhlog10_2lo = 3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */ 312116Sjkh 322116Sjkhstatic const double zero = 0.0; 332116Sjkh 3497413Salfreddouble 35117912Speter__ieee754_log10(double x) 362116Sjkh{ 37219360Sdas double f,hi,lo,y,z; 382116Sjkh int32_t i,k,hx; 392116Sjkh u_int32_t lx; 402116Sjkh 412116Sjkh EXTRACT_WORDS(hx,lx,x); 422116Sjkh 432116Sjkh k=0; 442116Sjkh if (hx < 0x00100000) { /* x < 2**-1022 */ 452116Sjkh if (((hx&0x7fffffff)|lx)==0) 462116Sjkh return -two54/zero; /* log(+-0)=-inf */ 472116Sjkh if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ 482116Sjkh k -= 54; x *= two54; /* subnormal number, scale up x */ 492116Sjkh GET_HIGH_WORD(hx,x); 502116Sjkh } 512116Sjkh if (hx >= 0x7ff00000) return x+x; 522116Sjkh k += (hx>>20)-1023; 53219360Sdas hx &= 0x000fffff; 54219360Sdas i = (hx+0x95f64)&0x100000; 55219360Sdas SET_HIGH_WORD(x,hx|(i^0x3ff00000)); /* normalize x or x/2 */ 56219360Sdas k += (i>>20); 57219360Sdas y = (double)k; 58219360Sdas f = __kernel_log(x); 59219360Sdas hi = x = x - 1; 60219360Sdas SET_LOW_WORD(hi,0); 61219360Sdas lo = x - hi; 62219360Sdas z = y*log10_2lo + (x+f)*ivln10lo + (lo+f)*ivln10hi + hi*ivln10hi; 632116Sjkh return z+y*log10_2hi; 642116Sjkh} 65