price_conv.c

/* GDCHART 0.10.0dev  PRICE_CONV.C  2 Nov 2000 */
/* Copyright Bruce Verderaime 1998-2004 */

/* 
*  - price as float to a string (ostensibly for printing)
*/

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <math.h>

/* ----------------------------------------------------------------- */
/* -- convert a float to a printable string, in form:             -- */
/* --   W N/D                                                     -- */
/* -- where W is whole, N is numerator, D is denominator          -- */
/* -- the frac N/D is one of 2nds, 4,8,16,32,64,128,256ths        -- */
/* -- if cannot convert, return str of the float                  -- */
/* ----------------------------------------------------------------- */

#define EPSILON     ((1.0/256.0)/2.0)
#define GET_DEC(x)  ( (x) - (float)(int)(x) )

char*
price_to_str( float price,
              int   *numorator,
              int   *demoninator,
              int   *decimal,
              char  *fltfmt )           /* printf fmt'ing str */
{
    static char rtn[64];
    int         whole = (int)price;
    float       dec   = GET_DEC( price ),
                numr;
    /* float        pow( double, double ); */

    /* caller doesn't want fractions */
    if( fltfmt )
        {
        sprintf( rtn, fltfmt, price );
        *numorator = *demoninator = *decimal = 0;
        return rtn;
        }

    numr = dec * 256;
    /* check if we have a perfect fration in 256ths */
    {   
        float   rdec = GET_DEC( numr );

        if( rdec < EPSILON )
            ;                           /* close enough to frac */
        else if( (1-rdec) < EPSILON )   /* just over but close enough */
            ++numr;
        else                            /* no frac match */
        {
            sprintf( rtn, "%f", price );
            *numorator = *demoninator = *decimal = 0;
            return rtn;
        }
    }

    /* now have numr 256ths */
    /* resolve down */
    if( numr != 0 )
        {
        int cnt = 8;

        while( (float)(numr)/2.0 == (float)(int)(numr/2) )
            {
            numr /= 2;
            --cnt;
            }

        /* don't want both whole AND numerator to be - */
        if( whole<0 && numr<0.0 )
            numr = -numr;
        *numorator = (int)numr;
        *demoninator = (int)pow(2.0, (float)cnt);
        *decimal = whole;
        sprintf( rtn, "%d %d/%d", whole,
                                  (int)numr,
                                  *demoninator );
        }
    else
        {
        *numorator = *demoninator = 0;
        *decimal = whole;
        sprintf( rtn, "%d", whole );
        }

    return rtn;
}