source: buchla-68k/orig/RAM/DEC2FR.C@ 0170798

/*
   =============================================================================
        dec2fr.c -- Buchla 700 fractional 2's complement conversion functions
        Version 10 -- 1987-12-06 -- D.N. Lynx Crowe
   =============================================================================
*/

#define TESTER  0

#include "stddefs.h"

#define SFACT   1000L           /* scale factor */

static long d2f[][10] = {       /* decimal to fraction table */

        {0x00000000L, 0x000019A0L, 0x00003336L, 0x00004CD0L, 0x00006668L,
         0x00008000L, 0x000099A0L, 0x0000B336L, 0x0000CCCEL, 0x0000E668L},

        {0x00000000L, 0x00000290L, 0x00000520L, 0x000007B0L, 0x00000A40L,
         0x00000CD0L, 0x00000F60L, 0x000011F0L, 0x00001480L, 0x00001710L}
};

static long f2d[] = {           /* fraction to decimal table */

        50000L, 25000L, 12500L,  6250L,
         3125L,  1562L,   781L,   390L,
          195L,    97L,    48L,    24L,
           12L,     6L,     3L,     1L
};

/* 

*/

/*
   =============================================================================
        dec2fr() -- convert an ASCII decimal string to fractional binary

        The input string is 4 characters in the range 100- to 100+ inclusive.
        The result is a 2's complement binary fractional value.
   =============================================================================
*/

short
dec2fr(s)
register char *s;
{
        register short i;

        if (s[0] EQ '1') {

                if (s[1] EQ '0') {

                        if (s[2] EQ '0') {

                                if (s[3] EQ '-')
                                        return(0x8000);  /* -100 */
                                else
                                        return(0x7FFF);  /* +100 */

                        } else {

                                return(0xFFFF); /* ERROR */
                        }

                } else {

                        return(0xFFFF); /* ERROR */

                }

/* 

*/

        } else if (s[0] EQ '0') {

                i = (d2f[0][s[1] - '0'] + d2f[1][s[2] - '0']) >> 1;

                if (s[3] EQ '-') {

                        if (i) 
                                return(~i);     /* negative number */
                        else
                                return(0);      /* zero is always 0 */

                } else {

                        return(i);      /* positive number */
                }
        }

        return(0xFFFF); /* ERROR */
}

/* 

*/

/*
   =============================================================================
        fr2dec() -- convert a 2's complement fraction to decimal ASCII notation

        The input is a 2's complement binary fractional value.
        The result string is 4 characters in the range 100- to 100+ inclusive.
   =============================================================================
*/

char *
fr2dec(v, s)
register short v;
register char *s;
{
        register long acc, sc;
        register short i, p;

        if (v EQ 0x7FFF) {      /* +100 */

                sprintf(s, "100+");
                return(s);
        }

        if (v EQ 0x8000) {      /* -100 */

                sprintf(s, "100-");
                return(s);
        }

        if (v & 0x8000) {

                v = ~v;         /* negative number */
                p = '-';

        } else {

                p = '+';        /* positive number */
        }

        acc = 0;

        for (i = 0; i LT 15; i++)
                if (v & (1 << (14 - i)))
                        acc += f2d[i];

        sc = SFACT;
        acc /= sc;
        sprintf(s, "%03d%c", (short)acc, p);
        return(s);
}

/* 

*/

#if TESTER

#include "stdio.h"

extern  int     memcmp();

char t[8], v[8];

/*
   =============================================================================
        test program for fractional two's complement conversion functions
   =============================================================================
*/

main()
{
        register short i;
        register short u;

        for (i = 0; i < 101; i++) {

                if (i EQ 50)
                        printf("\f");

                sprintf(t, "%03d+", i);
                u = dec2fr(t);

                if (u EQ 0xFFFF) {

                        printf("[%s] = ERROR  = ??????    ", t);

                } else {

                        fr2dec(u, v);
                        printf("[%s] = 0x%04x = [%s]", t, u, v);
                }

                printf(" %s    ", memcmp(t, v, 4) ? "<--" : "   ");

                sprintf(t, "%03d-", i);
                u = dec2fr(t);

                if (u EQ 0xFFFF) {

                        printf("    [%s] = ERROR  = ??????\n", t);

                } else {

                        fr2dec(u, v);
                        printf("    [%s] = 0x%04x = [%s]", t, u, v);
                }

                printf(" %s\n", memcmp(t, v, 4) ? "<--" : "");

        }
}

#endif