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#

# include "stdio.h"
# include "ctype.h"
# include "streams.h"
# define  nexttry           ((high+low)/2)

/*  alpha_seek(stream, word, s_size, fold)
        seeks the first line in stream that is at least word.
    assumes that stream is a sorted file of lines.  (last char must be \n)
    if fold, assumes that word is lowercase and folds stream to lowercase.
    s_size = size of stream
    returns 1 if word = line, 0 o.w.
*/
int alpha_seek(stream, word, s_size, fold)
FILE *stream;
char *word;
long int s_size;
int  fold;
{   
	long int high, low, mid;    /*  point to beginning of a line in stream  */
	int      ans;               /*  line(low) < word <= line(high)          */
	char     line[maxstr];


	/*  initialize low (return if first line >= word)       */
	low= 0L;
	pos(low); 
	getline(stream, line);
	if (fold) foldline(line);
	ans= strcmp(line,word);

	if ( ans >= 0)
	{   
		pos(low);   
		return(ans==0); 
	}

	/*  initialize high to "line" after last line           */
	high= s_size;

	mid= nextline(stream, nexttry );
	while (mid < high )
	{   
		getline(stream,line);
		if (fold) foldline(line);
		if (strcmp(line,word) < 0)    low=  mid;
		else high= mid;
		mid= nextline(stream, nexttry );
	}

	/* linear search from low to high   */
	low= nextline(stream,low);
	for(;;)
	{   
		if (low>=high)      break;

		getline(stream,line);
		if (fold) foldline(line);
		ans=strcmp(line,word);

		if (ans>=0)         break;
		low= ftell(stream);
	}

	pos(low);
	if (low==high)  return(0);
	else return(ans==0);
}


/*  foldline(p):    change all uppercase to lowercase in string p
*/
foldline(p)
char *p;
{   
	for (; *p!=NULL;  p++)
	{   
		if (isupper(*p))    *p = tolower(*p);
	}
}

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