autoconf/floatparam.c

   1 /* Determine some float parameters, much like gcc's "enquire.c". */
   2 /* Bruno Haible 24.8.1996 */
   3
   4 /* This program expects to be compiled by an ANSI C or C++ compiler. */
   5
   6 #include <stdio.h>
   7
   8 typedef int boolean;
   9 #define TRUE  1
  10 #define FALSE 0
  11
  12 typedef long double ldouble;
  13
  14 static void header (void)
  15 {
  16   printf("/* Rounding modes, for use below */\n");
  17   printf("#define rounds_to_nearest        0  /* 0.5 ulp */\n");
  18   printf("#define rounds_to_zero           1  /* 1 ulp */\n");
  19   printf("#define rounds_to_infinity       2  /* 1 ulp */\n");
  20   printf("#define rounds_to_minus_infinity 3  /* 1 ulp */\n");
  21   printf("\n");
  22 }
  23
  24 #define check(type,typeprefix,typestr,equalfn,mainfn)  \
  25 static boolean equalfn (volatile type* x, volatile type* y);            \
  26 static void mainfn (void)                                               \
  27 {                                                                       \
  28   int mant_bits;                                                        \
  29   int epsilon_bits = -1;                                                \
  30   int negepsilon_bits = -1;                                             \
  31   { type x = 1.0; type y; type z;                                       \
  32     for (y = 1.0; ; y = 0.5*y)                                          \
  33       { z = x + y; if (equalfn(&x,&z)) break;                           \
  34         z = z - x; if (!equalfn(&y,&z)) break;                          \
  35         epsilon_bits++;                                                 \
  36   }   }                                                                 \
  37   { type x = 1.0; type y; type z;                                       \
  38     for (y = -1.0; ; y = 0.5*y)                                         \
  39       { z = x + y; if (equalfn(&x,&z)) break;                           \
  40         z = z - x; if (!equalfn(&y,&z)) break;                          \
  41         negepsilon_bits++;                                              \
  42   }   }                                                                 \
  43   printf("/* Properties of type `%s': */\n",typestr);                   \
  44   printf("/* Largest n for which 1+2^(-n) is exactly represented is %d. */\n",epsilon_bits); \
  45   printf("/* Largest n for which 1-2^(-n) is exactly represented is %d. */\n",negepsilon_bits); \
  46   if (negepsilon_bits <= epsilon_bits)                                  \
  47     { printf("#error \"No exponent jump at 1.0 for type %s!\"\n",typestr); \
  48       mant_bits = -1;                                                   \
  49     }                                                                   \
  50   else                                                                  \
  51     { if (negepsilon_bits > epsilon_bits+1)                             \
  52         printf("/* Base for type `%s' is 2^%d\n",typestr,negepsilon_bits-epsilon_bits); \
  53       mant_bits = epsilon_bits+1;                                       \
  54       printf("#define %s_mant_bits %d\n",typeprefix,mant_bits);         \
  55     }                                                                   \
  56   { int i; type x, y1, y2, ys1, ys2, z1, z2, zs1, zs2;                  \
  57     x = 1.0; for (i = 0; i < epsilon_bits; i++) { x = 0.5*x; }          \
  58     y1 = 1.0 + 5.0*x; y2 = 1.0 + 6.0*x;                                 \
  59     ys1 = 1.0 + 5.4*x; ys2 = 1.0 + 5.6*x;                               \
  60     z1 = -1.0 + (-5.0)*x; z2 = -1.0 + (-6.0)*x;                         \
  61     zs1 = -1.0 + (-5.4)*x; zs2 = -1.0 + (-5.6)*x;                       \
  62     if (equalfn(&ys1,&y1) && equalfn(&ys2,&y2) && equalfn(&zs1,&z1) && equalfn(&zs2,&z2)) \
  63       printf("#define %s_rounds rounds_to_nearest\n",typeprefix);       \
  64     else if (equalfn(&ys1,&y1) && equalfn(&ys2,&y1) && equalfn(&zs1,&z1) && equalfn(&zs2,&z1)) \
  65       printf("#define %s_rounds rounds_to_zero\n",typeprefix);          \
  66     else if (equalfn(&ys1,&y2) && equalfn(&ys2,&y2) && equalfn(&zs1,&z1) && equalfn(&zs2,&z1)) \
  67       printf("#define %s_rounds rounds_to_infinity\n",typeprefix);      \
  68     else if (equalfn(&ys1,&y1) && equalfn(&ys2,&y1) && equalfn(&zs1,&z2) && equalfn(&zs2,&z2)) \
  69       printf("#define %s_rounds rounds_to_minus_infinity\n",typeprefix); \
  70     else                                                                \
  71       printf("#error \"Unknown rounding mode for type %s!\"\n",typestr); \
  72   }                                                                     \
  73   printf("\n");                                                         \
  74 }                                                                       \
  75 static boolean equalfn (volatile type* x, volatile type* y)             \
  76 {                                                                       \
  77   return *x == *y;                                                      \
  78 }                                                                       \
  79
  80 check(float,"float","float",equal_float,main_float)
  81 check(double,"double","double",equal_double,main_double)
  82 check(ldouble,"long_double","long double",equal_ldouble,main_ldouble)
  83
  84 /* Some systems (arm/linux) store doubles as little endian but with higher
  85  * and lower word reversed. */
  86 static void flipped_double (void)
  87 {
  88   typedef struct { unsigned lo, hi; } dfloat;
  89   union { dfloat eksplicit; double machine_double; } x;
  90   x.machine_double = 2;
  91   dfloat test = x.eksplicit;
  92   if (test.lo==0 && test.hi!=0) {
  93     printf("#define double_wordorder_bigendian_p 0\n");
  94   } else if (test.lo!=0 && test.hi==0) {
  95     printf("#define double_wordorder_bigendian_p 1\n");
  96   } else {
  97     /* Dazed and confused!  Better not define anything.
  98          * Code should rely on CL_CPU_BIG_ENDIAN_P instead. */
  99   }
 100   printf("\n");
 101 }
 102
 103 int main(int argc, char *argv[])
 104 { if (freopen(argc==1 ? "conftest.h" : argv[1], "w", stdout) == NULL) return 1;
 105   header();
 106   main_float();
 107   main_double();
 108   main_ldouble();
 109   flipped_double();
 110
 111   if (ferror(stdout) || fclose(stdout)) return 1;
 112   return 0;
 113 }