Chief Delphi - Quick & Dirty float to string converter

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Quick & Dirty float to string converter

The following code sample will convert IEEE-754 32bit float/double as used in C18 to a string. There are some limitations, but it runs ok on my unix box. I haven't (and cannot at the moment) try this on PIC18F/RC. The hex binary test values were obtained by creating and populating a float variable under MPLAB and hand copying out the hex value for testing purposes. The unix box is native 64bit, so I may have messed up somewhere but thought I'd drop this 5-minute QnD code out for folks to look at/use if needed or wanted. I'm sure there is a better way, but its just Quick 'n Dirty so don't expect elegant/optimal/all-encompassing.

When run on unix it generates what looks like reasonable output:

alpha> ./printff
1.234567879
1.233999963
1234.000000000
1234567936.000000000
0.123399970
0.001233931
0.000012276

Should work with printff( (long)float-variable-name ).

Bud
PS Derived by reading http://en.wikipedia.org/wiki/IEEE_754

Code:

#include <stdio.h>



int main()

{

    printff( 0x3f9e0652 );        /*         f1 = 1.23456789;        */

    printff( 0x3f9df3b6 );        /*      f1 = 1.234                */

    printff( 0x449a4000 );        /*      f1 = 1234.0                */

    printff( 0x4e932c06 );        /*      f1 = 123456789.0        */

    printff( 0x3dfcb924 );        /*      f1 = 0.1234             */

    printff( 0x3aa1be2b );      /*      f1 = 0.001234           */

    printff( 0x374f07e5 );      /*      f1 = 0.00001234         */

}



void printff( long fbinary )

{

unsigned char sign;

unsigned char exp;

unsigned long mantissa;

int bits;

long whole;

long fraction;

long left;



    sign = 1;

    if ((fbinary & 0x80000000) != 0) sign = -1;

    exp = (fbinary & 0x7F800000) >> 23;

    mantissa = (fbinary & 0x007FFFFF);



    bits = (int)exp - (int)127;

    if (bits >= 0)

    {

        if (bits <= 30)

        {

            whole = 0x1;

            while (bits > 0)

            {

                whole <<= 1;

                if ((mantissa & 0x00400000) != 0)

                    whole |= 0x1;

                mantissa <<= 1;

                --bits;

            }

            printf( "%c%d.", ((sign == 1)?' ':'-'), whole );

        }

        else

        {

            // can't do yet

            printf( "**.****\n");

        }



        fraction = 0;

        left     = 500000000;

        while (mantissa != 0)

        {

            if ((mantissa & 0x00400000) != 0)

                fraction += left;

            mantissa <<= 1;

            left = left / 2;

        }

        printf( "%09d\n", fraction );

    }

    else

    {

        /* Number < 1.0 */

        printf( "%c0.", ((sign == 1)?' ':'-') );

        mantissa |= 0x00800000;

        bits = -bits;

        if (bits < 24 )

        {

            mantissa >>= bits;

            fraction = 0;

            left     = 500000000;

            while (mantissa != 0)

            {

                if ((mantissa & 0x00800000) != 0)

                    fraction += left;

                mantissa <<= 1;

                left = left / 2;

            }

            printf( "%09d\n", fraction );

        }

        else

        {

            printf( "%09d\n", 0 );

        }

    }

    return;

}

Re: Quick & Dirty float to string converter

nice job man, im sure it would be useful.

Re: Quick & Dirty float to string converter

Fixed a couple bugs.

Test cases run:
1.234567879
1.233999963
1234.000000000
1234567936.000000000
0.123399970
0.001233990
0.000012335
0.156250000
98.765434262
9.876543043
0.987654324

Code:

void printff( long fbinary )

{

char sign;

unsigned char exp;

int bias;

long data;

long left;



    sign = ' ';

    if ((fbinary & 0x80000000) != 0) sign = '-';



    exp = (fbinary & 0x7F800000) >> 23; 



    /* compute whole number */

    bias = (int)exp - (int)127;

    if (bias >= 0)

    {

        if (bias <= 30)

        {

            data = 0x1;

            while (bias > 0)

            {

                data <<= 1;

                if ((fbinary & 0x00400000) != 0)

                    data |= 0x1;

                fbinary <<= 1;

                --bias;

            }

            printf( "%c%d.", sign, data );

        }

        else

        {

            // can't do yet

            printf( "**.****\n");

            return;

        }



        /* compute fraction */

        data = 0;

        left = 500000000;

        fbinary &= 0x007FFFFF;

        while (fbinary != 0)

        {

            if ((fbinary & 0x00400000) != 0)

                data += left;

            fbinary <<= 1;

            fbinary &= 0x007FFFFF;

            left = left >> 1;

        }

        printf( "%09d\n", data );

    }

    else

    {

        /* Number < 1.0 */

        printf( "%c0.", sign );

        bias = -bias;

        if (bias < 24 )

        {

            data = 0;

            left = 500000000;

            fbinary &= 0x00FFFFFF;

            fbinary |= 0x00800000;

            fbinary >>= (bias-1);

            while (fbinary != 0)

            {

                if ((fbinary & 0x00800000) != 0)

                    data += left;

                fbinary <<= 1;

                fbinary &= 0x00FFFFFF;

                left = left >> 1;

            }

            printf( "%09d\n", data );

        }

        else

        {

            printf( "%09d\n", 0 );

        }

    }

    return;

}

PS I'm not trying to encourage the use of floating point, but for debugging and in small doses it has its uses.