cpython/Modules/soundex.c

/*
  [Header: soundexmodule.c,v 1.2 95/05/02 15:40:45 dwwillia Exp ]
  
  Perform soundex comparisons on strings.

  Soundex is an algorithm that hashes English strings into numerical value.
  Strings that sound the same are hashed to the same value.  This allows 
  for non-literal string matching.

  From: David Wayne Williams <dwwillia@iucf.indiana.edu>

  Apr 29 1996 - added get_soundex method that returns the soundex of a
                string (chrish@qnx.com)
  May 2 1996  - added doc strings (chrish@qnx.com)
*/

#include <string.h>
#include <ctype.h>
#include "Python.h"

static char soundex_module__doc__[] =
"Perform Soundex comparisons on strings, allowing non-literal matching.";

static void soundex_hash(char *str, char *result)
{
    char *sptr = str;           /* pointer into str */
    char *rptr = result;        /* pointer into result */
    
    if(*str == '\0')
    {
        strcpy(result,"000000");
        return;
    }
            
    /*  Preserve the first character of the input string.
     */
    *(rptr++) = toupper(*(sptr++));
    
    /* Translate the rest of the input string into result.  The following
       transformations are used:

       1) All vowels, W, and H, are skipped.

       2) BFPV = 1
          CGJKQSXZ = 2
          DT = 3
          L = 4
          MN = 5
          R = 6

       3) Only translate the first of adjacent equal translations.  I.E.
          remove duplicate digits.
    */

    for(;(rptr - result) < 6 &&  *sptr != '\0';sptr++)
    {
        switch (toupper(*sptr))
        {
        case 'W':
        case 'H':
        case 'A':
        case 'I':
        case 'O':
        case 'U':
        case 'Y':
            break;
        case 'B':
        case 'F':
        case 'P':
        case 'V':
            if(*(rptr - 1) != '1')
                *(rptr++) = '1';
            break;
        case 'C':
        case 'G':
        case 'J':
        case 'K':
        case 'Q':
        case 'S':
        case 'X':
        case 'Z':
            if(*(rptr - 1) != '2')
                *(rptr++) = '2';
            break;
        case 'D':
        case 'T':
            if(*(rptr - 1) != '3')
                *(rptr++) = '3';
            break;
        case 'L':
            if(*(rptr - 1) != '4')
                *(rptr++) = '4';
            break;
        case 'M':
        case 'N':
            if(*(rptr - 1) != '5')
                *(rptr++) = '5';
            break;
        case 'R':
            if(*(rptr -1) != '6')
                *(rptr++) = '6';
        default:
            break;
        }
    }

    /* Pad 0's on right side of string out to 6 characters.
     */
    for(; rptr < result + 6; rptr++)
        *rptr = '0';

    /* Terminate the result string.
     */
    *(result + 6) = '\0';
}


/* Return the actual soundex value.         */
/* Added by Chris Herborth (chrish@qnx.com) */
static char soundex_get_soundex__doc__[] =
	"Return the (English) Soundex hash value for a string.";
static PyObject *
get_soundex(PyObject *self, PyObject *args)
{
	char *str;
	char sdx[7];

	if(!PyArg_ParseTuple( args, "s:get_soundex", &str))
	  return NULL;

	soundex_hash(str, sdx);

	return PyString_FromString(sdx);
}

static char soundex_sound_similar__doc__[] =
	"Compare two strings to see if they sound similar (English).";
static PyObject *
sound_similar(PyObject *self, PyObject *args)
{
    char *str1, *str2;
    char res1[7], res2[7];
    
    if(!PyArg_ParseTuple(args, "ss:sound_similar", &str1, &str2))
        return NULL;

    soundex_hash(str1, res1);
    soundex_hash(str2, res2);

    if(!strcmp(res1,res2))
        return Py_BuildValue("i",1);
    else
        return Py_BuildValue("i",0);
}

/* Python Method Table.
 */
static PyMethodDef SoundexMethods[] =
{
	{"sound_similar", sound_similar, 1, soundex_sound_similar__doc__},
	{"get_soundex", get_soundex, 1, soundex_get_soundex__doc__},

    {NULL, NULL }               /* sentinel */
};


/* Register the method table.
 */
DL_EXPORT(void)
initsoundex()
{
    (void) Py_InitModule4("soundex",
			  SoundexMethods,
			  soundex_module__doc__,
			  (PyObject *)NULL,
			  PYTHON_API_VERSION);
}