/*
 *------------------------------------------------------------------------
 *			substring->symbol
 *
 * Converting a substring to a Scheme symbol
 *
 * This C code implements a function substring->symbol:
 *	substring->symbol STR BEG END
 * which converts a substring of STR to a symbol. The function can be
 * defined as
 *      (define (substring->symbol STR BEG END)
 *	    (string->symbol (substring STR BEG END)))
 * However, the current C version is faster and produces no garbage
 * in case the resulting symbol has already been seen. This function
 * can be regarded as a "shared substring" implementation of the
 * above code.
 *
 * To use this efficient version in your Scheme code, you have to add
 * (extern (substring->symbol::symbol (::bstring ::int ::int)    
 *		"substring_to_symbol")
 *	   (include "substring-symbol.c"))
 * (pragma
 * 	   (substring->symbol no-cfa-top nesting))
 * to your module declaration. Note the 'include' clause will insert this
 * present file into the C code generated by the Bigloo compiler.
 * Therefore, you should not compile this file separately.
 *
 * This code is specific to the Bigloo Scheme system by Manuel Serrano.
 *
 * The code is almost entirely based on a function 'string_to_symbol'
 * in bigloo2.4b/runtime/Clib/csymbol.c of Bigloo distribution,
 * and c_substring of the bigloo2.4b/runtime/Clib/cstring.c 
 *
 * Note, the previous version of this function had the signature
 * (substring->symbol::symbol (::string ::int ::int)    
 *		"substring_to_symbol")
 * that is, substring_to_symbol accepted a C string rather than Scheme
 * (Bigloo) string as its first argument. That was markedly slower:
 * slower than the composition of string->symbol and substring! The
 * reason is that ::bstring has its length easily available, while
 * the length of the ::string has to be computed, by strlen(). Note
 * that substring->symbol is called by next-token-of-as-symb, which
 * passes the input buffer as the first argument of substring->symbol.
 * The input buffer is typically a large string. As it turns out,
 * the cost of calling strlen repeatedly adds up. The present version
 * is roughly 30% faster than the composition of string->symbol and
 * substring, whereas the previous version of this function was 30% slower!
 *
 * $Id: substring-symbol.c,v 1.4 2002/06/06 17:03:40 oleg Exp $
 *------------------------------------------------------------------------
 */

/*
 * The following two #include only needed if this file is compiled
 * separately, rather than included
 #include <string.h>
 #include <bigloo.h>
*/
#include <assert.h>

extern obj_t string_to_symbol( char * );

obj_t
substring_to_symbol(obj_t str, const int beg, const int end)
{
  const int total_len = str->string_t.length;

#if 0
  printf("\nIn substring_to_symbol: %d %d '%.20s' %x\n",beg,end,BSTRING_TO_STRING(str),BSTRING_TO_STRING(str));
#endif

  assert( beg >= 0 && beg < total_len );
  if( end == total_len )
    return string_to_symbol(&STRING_REF( str, beg ));

  assert( end >= 0 && end < total_len );
  {
    char * name = BSTRING_TO_STRING(str);
    const char c = name[end];	/* Save the character at name[end] */
    obj_t symb;
    name[end] = '\0';		/* Forcibly terminate the string */
    symb = string_to_symbol(name+beg);
    name[end] = c;		/* Restore the char name[end] */
    return symb;
  }
}