arithchk.c

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Copyright (C) 1997, 1998 Lucent Technologies
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/* Try to deduce arith.h from arithmetic properties. */

#include <stdio.h>

static int dalign;
typedef struct Akind
{
    char* name;
    int kind;
} Akind;

static Akind IEEE_8087 = {"IEEE_8087", 1}, IEEE_MC68k = {"IEEE_MC68k", 2}, IBM = {"IBM", 3},
             VAX = {"VAX", 4}, CRAY = {"CRAY", 5};

static Akind* Lcheck()
{
    union
    {
        double d;
        long L[2];
    } u;
    struct
    {
        double d;
        long L;
    } x[2];

    if(sizeof(x) > 2 * (sizeof(double) + sizeof(long)))
        dalign = 1;
    u.L[0] = u.L[1] = 0;
    u.d = 1e13;
    if(u.L[0] == 1117925532 && u.L[1] == -448790528)
        return &IEEE_MC68k;
    if(u.L[1] == 1117925532 && u.L[0] == -448790528)
        return &IEEE_8087;
    if(u.L[0] == -2065213935 && u.L[1] == 10752)
        return &VAX;
    if(u.L[0] == 1267827943 && u.L[1] == 704643072)
        return &IBM;
    return 0;
}

static Akind* icheck()
{
    union
    {
        double d;
        int L[2];
    } u;
    struct
    {
        double d;
        int L;
    } x[2];

    if(sizeof(x) > 2 * (sizeof(double) + sizeof(int)))
        dalign = 1;
    u.L[0] = u.L[1] = 0;
    u.d = 1e13;
    if(u.L[0] == 1117925532 && u.L[1] == -448790528)
        return &IEEE_MC68k;
    if(u.L[1] == 1117925532 && u.L[0] == -448790528)
        return &IEEE_8087;
    if(u.L[0] == -2065213935 && u.L[1] == 10752)
        return &VAX;
    if(u.L[0] == 1267827943 && u.L[1] == 704643072)
        return &IBM;
    return 0;
}

static Akind* ccheck()
{
    union
    {
        double d;
        long L;
    } u;
    long Cray1;

    /* Cray1 = 4617762693716115456 -- without overflow on non-Crays */
    Cray1 = printf("") < 0 ? 0 : 4617762;
    if(printf("%ld", Cray1) >= 0)
        Cray1 = 1000000 * Cray1 + 693716;
    if(printf("%ld", Cray1) >= 0)
        Cray1 = 1000000 * Cray1 + 115456;
    u.d = 1e13;
    if(u.L == Cray1)
        return &CRAY;
    return 0;
}

static int fzcheck()
{
    double a, b;
    int i;

    a = 1.;
    b = .1;
    for(i = 155;; b *= b, i >>= 1)
    {
        if(i & 1)
        {
            a *= b;
            if(i == 1)
                break;
        }
    }
    b = a * a;
    return b == 0.;
}

int main()
{
    Akind* a = 0;
    int Ldef = 0;
    FILE* f;

#ifdef WRITE_ARITH_H /* for Symantec's buggy "make" */
    f = fopen("arith.h", "w");
    if(!f)
    {
        printf("Cannot open arith.h\n");
        return 1;
    }
#else
    f = stdout;
#endif

    if(sizeof(double) == 2 * sizeof(long))
        a = Lcheck();
    else if(sizeof(double) == 2 * sizeof(int))
    {
        Ldef = 1;
        a = icheck();
    }
    else if(sizeof(double) == sizeof(long))
        a = ccheck();
    if(a)
    {
        fprintf(f, "#define %s\n#define Arith_Kind_ASL %d\n", a->name, a->kind);
        if(Ldef)
            fprintf(f, "#define Long int\n#define Intcast (int)(long)\n");
        if(dalign)
            fprintf(f, "#define Double_Align\n");
        if(sizeof(char*) == 8)
            fprintf(f, "#define X64_bit_pointers\n");
#ifndef NO_LONG_LONG
        if(sizeof(long long) < 8)
#endif
            fprintf(f, "#define NO_LONG_LONG\n");
        if(a->kind <= 2 && fzcheck())
            fprintf(f, "#define Sudden_Underflow\n");
#ifdef WRITE_ARITH_H
        fclose(f);
#endif
        return 0;
    }
    fprintf(f, "/* Unknown arithmetic */\n");

#ifdef WRITE_ARITH_H
    fclose(f);
#endif

    return 1;
}