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Annotation of src/lib/libm/src/e_logf.c, Revision 1.8

1.1       jtc         1: /* e_logf.c -- float version of e_log.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
1.7       simonb     11:  * software is freely granted, provided that this notice
1.1       jtc        12:  * is preserved.
                     13:  * ====================================================
                     14:  */
                     15:
1.5       lukem      16: #include <sys/cdefs.h>
1.3       jtc        17: #if defined(LIBM_SCCS) && !defined(lint)
1.8     ! wiz        18: __RCSID("$NetBSD: e_logf.c,v 1.7 1999/07/02 15:37:40 simonb Exp $");
1.1       jtc        19: #endif
                     20:
                     21: #include "math.h"
                     22: #include "math_private.h"
                     23:
                     24: static const float
                     25: ln2_hi =   6.9313812256e-01,   /* 0x3f317180 */
                     26: ln2_lo =   9.0580006145e-06,   /* 0x3717f7d1 */
                     27: two25 =    3.355443200e+07,    /* 0x4c000000 */
                     28: Lg1 = 6.6666668653e-01,        /* 3F2AAAAB */
                     29: Lg2 = 4.0000000596e-01,        /* 3ECCCCCD */
                     30: Lg3 = 2.8571429849e-01, /* 3E924925 */
                     31: Lg4 = 2.2222198546e-01, /* 3E638E29 */
                     32: Lg5 = 1.8183572590e-01, /* 3E3A3325 */
                     33: Lg6 = 1.5313838422e-01, /* 3E1CD04F */
                     34: Lg7 = 1.4798198640e-01; /* 3E178897 */
                     35:
                     36: static const float zero   =  0.0;
                     37:
1.8     ! wiz        38: float
        !            39: __ieee754_logf(float x)
1.1       jtc        40: {
                     41:        float hfsq,f,s,z,R,w,t1,t2,dk;
1.2       jtc        42:        int32_t k,ix,i,j;
1.1       jtc        43:
                     44:        GET_FLOAT_WORD(ix,x);
                     45:
                     46:        k=0;
                     47:        if (ix < 0x00800000) {                  /* x < 2**-126  */
1.7       simonb     48:            if ((ix&0x7fffffff)==0)
1.1       jtc        49:                return -two25/zero;             /* log(+-0)=-inf */
                     50:            if (ix<0) return (x-x)/zero;        /* log(-#) = NaN */
                     51:            k -= 25; x *= two25; /* subnormal number, scale up x */
                     52:            GET_FLOAT_WORD(ix,x);
1.7       simonb     53:        }
1.1       jtc        54:        if (ix >= 0x7f800000) return x+x;
                     55:        k += (ix>>23)-127;
                     56:        ix &= 0x007fffff;
                     57:        i = (ix+(0x95f64<<3))&0x800000;
                     58:        SET_FLOAT_WORD(x,ix|(i^0x3f800000));    /* normalize x or x/2 */
                     59:        k += (i>>23);
                     60:        f = x-(float)1.0;
                     61:        if((0x007fffff&(15+ix))<16) {   /* |f| < 2**-20 */
1.6       thorpej    62:            if(f==zero) { if(k==0) return zero;  else {dk=(float)k;
                     63:                                   return dk*ln2_hi+dk*ln2_lo;}
                     64:            }
1.1       jtc        65:            R = f*f*((float)0.5-(float)0.33333333333333333*f);
                     66:            if(k==0) return f-R; else {dk=(float)k;
                     67:                     return dk*ln2_hi-((R-dk*ln2_lo)-f);}
                     68:        }
1.7       simonb     69:        s = f/((float)2.0+f);
1.1       jtc        70:        dk = (float)k;
                     71:        z = s*s;
                     72:        i = ix-(0x6147a<<3);
                     73:        w = z*z;
                     74:        j = (0x6b851<<3)-ix;
1.7       simonb     75:        t1= w*(Lg2+w*(Lg4+w*Lg6));
                     76:        t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
1.1       jtc        77:        i |= j;
                     78:        R = t2+t1;
                     79:        if(i>0) {
                     80:            hfsq=(float)0.5*f*f;
                     81:            if(k==0) return f-(hfsq-s*(hfsq+R)); else
                     82:                     return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
                     83:        } else {
                     84:            if(k==0) return f-s*(f-R); else
                     85:                     return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
                     86:        }
                     87: }