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120 lines
4.3 KiB
120 lines
4.3 KiB
/* Determine some float parameters, much like gcc's "enquire.c". */
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/* Bruno Haible 24.8.1996 */
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/* This program expects to be compiled by an ANSI C or C++ compiler. */
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#include <stdio.h>
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#if !(defined(__STDC__) || defined(__cplusplus))
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/* Only for use in function parameter lists and as function return type. */
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#define void
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#endif
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typedef int boolean;
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#define TRUE 1
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#define FALSE 0
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#ifdef HAVE_LONGDOUBLE
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typedef long double ldouble;
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#endif
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static void header (void)
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{
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printf("/* Rounding modes, for use below */\n");
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printf("#define rounds_to_nearest 0 /* 0.5 ulp */\n");
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printf("#define rounds_to_zero 1 /* 1 ulp */\n");
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printf("#define rounds_to_infinity 2 /* 1 ulp */\n");
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printf("#define rounds_to_minus_infinity 3 /* 1 ulp */\n");
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printf("\n");
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}
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#define check(type,typeprefix,typestr,equalfn,mainfn) \
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static boolean equalfn (type* x, type* y); \
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static void mainfn (void) \
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{ \
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int mant_bits; \
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int epsilon_bits = -1; \
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int negepsilon_bits = -1; \
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{ type x = 1.0; type y; type z; \
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for (y = 1.0; ; y = 0.5*y) \
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{ z = x + y; if (equalfn(&x,&z)) break; \
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z = z - x; if (!equalfn(&y,&z)) break; \
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epsilon_bits++; \
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} } \
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{ type x = 1.0; type y; type z; \
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for (y = -1.0; ; y = 0.5*y) \
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{ z = x + y; if (equalfn(&x,&z)) break; \
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z = z - x; if (!equalfn(&y,&z)) break; \
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negepsilon_bits++; \
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} } \
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printf("/* Properties of type `%s': */\n",typestr); \
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printf("/* Largest n for which 1+2^(-n) is exactly represented is %d. */\n",epsilon_bits); \
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printf("/* Largest n for which 1-2^(-n) is exactly represented is %d. */\n",negepsilon_bits); \
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if (negepsilon_bits <= epsilon_bits) \
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{ printf("#error \"No exponent jump at 1.0 for type %s!\"\n",typestr); \
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mant_bits = -1; \
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} \
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else \
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{ if (negepsilon_bits > epsilon_bits+1) \
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printf("/* Base for type `%s' is 2^%d\n",typestr,negepsilon_bits-epsilon_bits); \
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mant_bits = epsilon_bits+1; \
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printf("#define %s_mant_bits %d\n",typeprefix,mant_bits); \
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} \
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{ int i; type x, y1, y2, ys1, ys2, z1, z2, zs1, zs2; \
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x = 1.0; for (i = 0; i < epsilon_bits; i++) { x = 0.5*x; } \
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y1 = 1.0 + 5.0*x; y2 = 1.0 + 6.0*x; \
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ys1 = 1.0 + 5.4*x; ys2 = 1.0 + 5.6*x; \
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z1 = -1.0 + (-5.0)*x; z2 = -1.0 + (-6.0)*x; \
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zs1 = -1.0 + (-5.4)*x; zs2 = -1.0 + (-5.6)*x; \
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if (equalfn(&ys1,&y1) && equalfn(&ys2,&y2) && equalfn(&zs1,&z1) && equalfn(&zs2,&z2)) \
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printf("#define %s_rounds rounds_to_nearest\n",typeprefix); \
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else if (equalfn(&ys1,&y1) && equalfn(&ys2,&y1) && equalfn(&zs1,&z1) && equalfn(&zs2,&z1)) \
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printf("#define %s_rounds rounds_to_zero\n",typeprefix); \
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else if (equalfn(&ys1,&y2) && equalfn(&ys2,&y2) && equalfn(&zs1,&z1) && equalfn(&zs2,&z1)) \
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printf("#define %s_rounds rounds_to_infinity\n",typeprefix); \
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else if (equalfn(&ys1,&y1) && equalfn(&ys2,&y1) && equalfn(&zs1,&z2) && equalfn(&zs2,&z2)) \
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printf("#define %s_rounds rounds_to_minus_infinity\n",typeprefix); \
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else \
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printf("#error \"Unknown rounding mode for type %s!\"\n",typestr); \
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} \
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printf("\n"); \
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} \
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static boolean equalfn (type* x, type* y) { return *x == *y; } \
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check(float,"float","float",equal_float,main_float)
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check(double,"double","double",equal_double,main_double)
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#ifdef HAVE_LONGDOUBLE
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check(ldouble,"long_double","long double",equal_ldouble,main_ldouble)
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#endif
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/* Some systems (arm/linux) store doubles as little endian but with higher
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* and lower word reversed. */
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static void flipped_double (void)
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{
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typedef struct { unsigned lo, hi; } dfloat;
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double x = 2;
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dfloat test = *(dfloat*)&x;
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if (test.lo==0 && test.hi!=0) {
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printf("#define double_wordorder_bigendian_p 0\n");
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} else if (test.lo!=0 && test.hi==0) {
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printf("#define double_wordorder_bigendian_p 1\n");
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} else {
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/* Dazed and confused! Better not define anything.
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* Code should rely on CL_CPU_BIG_ENDIAN_P instead. */
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}
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printf("\n");
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}
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int main()
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{
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header();
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main_float();
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main_double();
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#ifdef HAVE_LONGDOUBLE
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main_ldouble();
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#endif
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flipped_double();
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if (ferror(stdout)) return 1;
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return 0;
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}
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