From  http://www.census.gov/geo/msb/stand/strcmp.c
----- C source -------
/* jwcmp.c   Version 2                              */

/* The strcmp95 function returns a double precision value from 0.0 (to
+tal
   disagreement) to 1.0 (character-by-character agreement).  The retur
+ned 
   value is a measure of the similarity of the two strings.           
+        */

/* Date of Release:  Jan. 26, 1994                          */
/* Modified: April 24, 1994  Corrected the processing of the single le
+ngth
             character strings.
   Authors:  This function was written using the logic from code writt
+en by
             Bill Winkler, George McLaughlin and Matt Jaro with modifi
+cations
             by Maureen Lynch. 
   Comment:  This is the official string comparator to be used for mat
+ching 
             during the 1995 Test Census.                             
+        */

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

#define NOTNUM(c)    ((c>57) || (c<48))
#define INRANGE(c)      ((c>0)  && (c<91))
#define MAX_VAR_SIZE 61
#define NULL60 "                                                      
+      "

double  jwcmp(char *ying, char *yang, long y_length, int *ind_c[])

{
/* Arguments:

   ying and yang are pointers to the 2 strings to be compared.  The st
+rings
   need not be NUL-terminated strings because the length is passed.

   y_length is the length of the strings. 

   ind_c is an array that is used to define whether certain options sh
+ould be 
   activated.  A nonzero value indicates the option is deactivated.  
   The options are:
     ind_c[0] Increase the probability of a match when the number of m
+atched
              characters is large.  This option allows for a little mo
+re
              tolerance when the strings are large.  It is not an appr
+opriate
              test when comparing fixed length fields such as phone an
+d
              social security numbers.
     ind_c[1] All lower case characters are converted to upper case pr
+ior
              to the comparison.  Disabling this feature means that th
+e lower 
              case string "code" will not be recognized as the same as
+ the 
              upper case string "CODE".  Also, the adjustment for simi
+lar 
              characters section only applies to uppercase characters.

   The suggested values are all zeros for character strings such as na
+mes.    */

static    int    pass=0,    adjwt[91][91];
static    char    sp[39][2] =
 {'A','E',  'A','I',  'A','O',  'A','U',  'B','V',  'E','I',  'E','O',
+  'E','U',
  'I','O',  'I','U',  'O','U',  'I','Y',  'E','Y',  'C','G',  'E','F',
  'W','U',  'W','V',  'X','K',  'S','Z',  'X','S',  'Q','C',  'U','V',
  'M','N',  'L','I',  'Q','O',  'P','R',  'I','J',  '2','Z',  '5','S',
  '8','B',  '1','I',  '1','L',  '0','O',  '0','Q',  'C','K',  'G','J',
  'E',' ',  'Y',' ',  'S',' '};

char    ying_hold[MAX_VAR_SIZE],
        yang_hold[MAX_VAR_SIZE],
        ying_flag[MAX_VAR_SIZE],
        yang_flag[MAX_VAR_SIZE];

double  weight,    Num_sim;

long    minv,   search_range,   lowlim,    ying_length,
        hilim,  N_trans,        Num_com,   yang_length;

int    yl1,    yi_st,    N_simi;

register        int     i,      j,      k;

/* Initialize the adjwt array on the first call to the function only.
   The adjwt array is used to give partial credit for characters that 
   may be errors due to known phonetic or character recognition errors
+.
   A typical example is to match the letter "O" with the number "0"   
+        */
if (!pass) {
  pass++;
  for (i=0; i<91; i++) for (j=0; j<91; j++) adjwt[i][j] = 0;
  for (i=0; i<36; i++) {
    adjwt[sp[i][0]][sp[i][1]] = 3;
    adjwt[sp[i][1]][sp[i][0]] = 3;
} }

/* If either string is blank - return - added in Version 2            
+        */
if (!strncmp(ying,NULL60,y_length)) return(0.0);                 
if (!strncmp(yang,NULL60,y_length)) return(0.0);                 

/* Identify the strings to be compared by stripping off all leading an
+d 
   trailing spaces.                                  */
k = y_length - 1;
for(j = 0;((ying[j]==' ') && (j < k));j++);
for(i = k;((ying[i]==' ') && (i > 0));i--);
ying_length = i + 1 - j;
yi_st = j;

for(j = 0;((yang[j]==' ') && (j < k));j++);
for(i = k;((yang[i]==' ') && (i > 0));i--);
yang_length = i + 1 - j;

ying_hold[0]=yang_hold[0]=0;
strncat(ying_hold,&ying[yi_st],ying_length);
strncat(yang_hold,&yang[j],yang_length);

if (ying_length > yang_length) {
  search_range = ying_length;
  minv = yang_length;
  }
 else {
  search_range = yang_length;
  minv = ying_length;
  }

/* If either string is blank - return                                 
+        */
/* if (!minv) return(0.0);                   removed in version 2     
+        */

/* Blank out the flags                                  */
ying_flag[0] = yang_flag[0] = 0;
strncat(ying_flag,NULL60,search_range);
strncat(yang_flag,NULL60,search_range);
search_range = (search_range/2) - 1;
if (search_range < 0) search_range = 0;   /* added in version 2       
+        */

/* Convert all lower case characters to upper case.                   
+        */
if (!ind_c[1]) {
  for (i = 0;i < ying_length;i++) if (islower(ying_hold[i])) ying_hold
+[i] -= 32;
  for (j = 0;j < yang_length;j++) if (islower(yang_hold[j])) yang_hold
+[j] -= 32;
}

/* Looking only within the search range, count and flag the matched pa
+irs.    */
Num_com = 0; 
yl1 = yang_length - 1;
for (i = 0;i < ying_length;i++) {
  lowlim = (i >= search_range) ? i - search_range : 0;
  hilim = ((i + search_range) <= yl1) ? (i + search_range) : yl1;
  for (j = lowlim;j <= hilim;j++)  {
    if ((yang_flag[j] != '1') && (yang_hold[j] == ying_hold[i])) {
        yang_flag[j] = '1';
        ying_flag[i] = '1';
        Num_com++;
        break;
} } }

/* If no characters in common - return                                
+        */
if (!Num_com) return(0.0);                          

/* Count the number of transpositions                                 
+        */
k = N_trans = 0;
for (i = 0;i < ying_length;i++) {
  if (ying_flag[i] == '1') {
    for (j = k;j < yang_length;j++) {
        if (yang_flag[j] == '1') { 
         k = j + 1;
         break;
    } }
    if (ying_hold[i] != yang_hold[j]) N_trans++;
} }
N_trans = N_trans / 2;

/* adjust for similarities in nonmatched characters                   
+        */
N_simi = 0;
if (minv > Num_com) {   
  for (i = 0;i < ying_length;i++) {
    if (ying_flag[i] == ' ' && INRANGE(ying_hold[i])) { 
      for (j = 0;j < yang_length;j++) {
        if (yang_flag[j] == ' ' && INRANGE(yang_hold[j])) {
          if (adjwt[ying_hold[i]][yang_hold[j]] > 0) {
            N_simi += adjwt[ying_hold[i]][yang_hold[j]];
            yang_flag[j] = '2';
            break;
} } } } } }
Num_sim = ((double) N_simi)/10.0 + Num_com;

/* Main weight computation.                              */
weight= Num_sim / ((double) ying_length) + Num_sim / ((double) yang_le
+ngth)
   + ((double) (Num_com - N_trans)) / ((double) Num_com);
weight = weight / 3.0;

/* Continue to boost the weight if the strings are similar            
+        */
if (weight > 0.7) {

  /* Adjust for having up to the first 4 characters in common         
+        */
  j = (minv >= 4) ? 4 : minv;
  for (i=0;((i<j)&&(ying_hold[i]==yang_hold[i])&&(NOTNUM(ying_hold[i])
+));i++); 
  if (i) weight += i * 0.1 * (1.0 - weight);

  /* Optionally adjust for long strings.                              
+        */
  /* After agreeing beginning chars, at least two more must agree and 
       the agreeing characters must be > .5 of remaining characters.  
+        */
  if ((!ind_c[0]) && (minv>4) && (Num_com>i+1) && (2*Num_com>=minv+i))
+ 
  if (NOTNUM(ying_hold[0])) 
    weight += (double) (1.0-weight) *
   ((double) (Num_com-i-1) / ((double) (ying_length+yang_length-i*2+2)
+));
 }

return(weight);

} /* jwcmp */

----- end source ----
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