modernc.org/ccgo/v3@v3.16.14/lib/testdata/gcc-9.1.0/gcc/testsuite/gcc.c-torture/execute/cbrt.c (about)

     1  /*
     2   * ====================================================
     3   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     4   *
     5   * Developed at SunPro, a Sun Microsystems, Inc. business.
     6   * Permission to use, copy, modify, and distribute this
     7   * software is freely granted, provided that this notice
     8   * is preserved.
     9   * ====================================================
    10  */
    11  
    12  #ifndef __vax__
    13  static const unsigned long
    14  	B1 = 715094163, /* B1 = (682-0.03306235651)*2**20 */
    15  	B2 = 696219795; /* B2 = (664-0.03306235651)*2**20 */
    16  
    17  static const double
    18  	C =  5.42857142857142815906e-01, /* 19/35     = 0x3FE15F15, 0xF15F15F1 */
    19  	D = -7.05306122448979611050e-01, /* -864/1225 = 0xBFE691DE, 0x2532C834 */
    20  	E =  1.41428571428571436819e+00, /* 99/70     = 0x3FF6A0EA, 0x0EA0EA0F */
    21  	F =  1.60714285714285720630e+00, /* 45/28     = 0x3FF9B6DB, 0x6DB6DB6E */
    22  	G =  3.57142857142857150787e-01; /* 5/14      = 0x3FD6DB6D, 0xB6DB6DB7 */
    23  
    24  double
    25  cbrtl (double x)
    26  {
    27    long hx;
    28    double r,s,w;
    29    double lt;
    30    unsigned sign;
    31    typedef unsigned unsigned32 __attribute__((mode(SI)));
    32    union {
    33      double t;
    34      unsigned32 pt[2];
    35    } ut, ux;
    36    int n0;
    37  
    38    ut.t = 1.0;
    39    n0 = (ut.pt[0] == 0);
    40  
    41    ut.t = 0.0;
    42    ux.t = x;
    43  
    44    hx = ux.pt[n0];			/* high word of x */
    45    sign=hx&0x80000000;			/* sign= sign(x) */
    46    hx  ^=sign;
    47    if(hx>=0x7ff00000) return(x+x);	/* cbrt(NaN,INF) is itself */
    48    if((hx| ux.pt[1-n0])==0)
    49      return(ux.t);			/* cbrt(0) is itself */
    50  
    51    ux.pt[n0] = hx;
    52    /* rough cbrt to 5 bits */
    53    if(hx<0x00100000)			/* subnormal number */
    54      {ut.pt[n0]=0x43500000;		/* set t= 2**54 */
    55       ut.t*=x; ut.pt[n0]=ut.pt[n0]/3+B2;
    56     }
    57    else
    58      ut.pt[n0]=hx/3+B1;
    59  
    60    /* new cbrt to 23 bits, may be implemented in single precision */
    61    r=ut.t*ut.t/ux.t;
    62    s=C+r*ut.t;
    63    ut.t*=G+F/(s+E+D/s);
    64  
    65    /* chopped to 20 bits and make it larger than cbrt(x) */
    66    ut.pt[1-n0]=0; ut.pt[n0]+=0x00000001;
    67  
    68    /* one step newton iteration to 53 bits with error less than 0.667 ulps */
    69    s=ut.t*ut.t;				/* t*t is exact */
    70    r=ux.t/s;
    71    w=ut.t+ut.t;
    72    r=(r-ut.t)/(w+r);			/* r-s is exact */
    73    ut.t=ut.t+ut.t*r;
    74  
    75    /* restore the sign bit */
    76    ut.pt[n0] |= sign;
    77  
    78    lt = ut.t;
    79    lt -= (lt - (x/(lt*lt))) * 0.333333333333333333333;
    80    return lt;
    81  }
    82  
    83  main ()
    84  {
    85    if ((int) (cbrtl (27.0) + 0.5) != 3)
    86      abort ();
    87  
    88    exit (0);
    89  }
    90  #else
    91  main () { exit (0); }
    92  #endif