gonzui

    1: /* e_log10f.c -- float version of e_log10.c.
    2:  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
    3:  */
    4: 
    5: /*
    6:  * ====================================================
    7:  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
    8:  *
    9:  * Developed at SunPro, a Sun Microsystems, Inc. business.
   10:  * Permission to use, copy, modify, and distribute this
   11:  * software is freely granted, provided that this notice 
   12:  * is preserved.
   13:  * ====================================================
   14:  */
   15: 
   16: #include "math.h"
   17: #include "math_private.h"
   18: 
   19: static const float
   20: two25      =  3.3554432000e+07, /* 0x4c000000 */
   21: ivln10     =  4.3429449201e-01, /* 0x3ede5bd9 */
   22: log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
   23: log10_2lo  =  7.9034151668e-07; /* 0x355427db */
   24: 
   25: static const float zero   =  0.0;
   26: 
   27: float
   28: log10f(float x)
   29: {
   30:         float y,z;
   31:         int32_t i,k,hx;
   32: 
   33:         GET_FLOAT_WORD(hx,x);
   34: 
   35:         k=0;
   36:         if (hx < 0x00800000) {                  /* x < 2**-126  */
   37:             if ((hx&0x7fffffff)==0)
   38:                 return -two25/zero;             /* log(+-0)=-inf */
   39:             if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
   40:             k -= 25; x *= two25; /* subnormal number, scale up x */
   41:             GET_FLOAT_WORD(hx,x);
   42:         }
   43:         if (hx >= 0x7f800000) return x+x;
   44:         k += (hx>>23)-127;
   45:         i  = ((u_int32_t)k&0x80000000)>>31;
   46:         hx = (hx&0x007fffff)|((0x7f-i)<<23);
   47:         y  = (float)(k+i);
   48:         SET_FLOAT_WORD(x,hx);
   49:         z  = y*log10_2lo + ivln10*logf(x);
   50:         return  z+y*log10_2hi;
   51: }