diff.c: get rid of duplicate implementation

The implementations in diff.c to detect moved lines needs to compare
strings and hash strings, which is implemented in that file, as well
as in the xdiff library.

Remove the rather recent implementation in diff.c and rely on the well
exercised code in the xdiff lib.

With this change the hash used for bucketing the strings for the moved
line detection changes from FNV32 (that is provided via the hashmaps
memhash) to DJB2 (which is used internally in xdiff).  Benchmarks found
on the web[1] do not indicate that these hashes are different in
performance for readable strings.

[1] https://softwareengineering.stackexchange.com/questions/49550/which-hashing-algorithm-is-best-for-uniqueness-and-speedSigned-off-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

diff.c

@@ -707,88 +707,14 @@ struct moved_entry {
 	struct moved_entry *next_line;
 };
 
-static int next_byte(const char **cp, const char **endp,
-		     const struct diff_options *diffopt)
-{
-	int retval;
-
-	if (*cp >= *endp)
-		return -1;
-
-	if (isspace(**cp)) {
-		if (DIFF_XDL_TST(diffopt, IGNORE_WHITESPACE_CHANGE)) {
-			while (*cp < *endp && isspace(**cp))
-				(*cp)++;
-			/*
-			 * After skipping a couple of whitespaces,
-			 * we still have to account for one space.
-			 */
-			return (int)' ';
-		}
-
-		if (DIFF_XDL_TST(diffopt, IGNORE_WHITESPACE)) {
-			while (*cp < *endp && isspace(**cp))
-				(*cp)++;
-			/*
-			 * return the first non-ws character via the usual
-			 * below, unless we ate all of the bytes
-			 */
-			if (*cp >= *endp)
-				return -1;
-		}
-	}
-
-	retval = (unsigned char)(**cp);
-	(*cp)++;
-	return retval;
-}
-
 static int moved_entry_cmp(const struct diff_options *diffopt,
 			   const struct moved_entry *a,
 			   const struct moved_entry *b,
 			   const void *keydata)
 {
-	const char *ap = a->es->line, *ae = a->es->line + a->es->len;
-	const char *bp = b->es->line, *be = b->es->line + b->es->len;
-
-	if (!(diffopt->xdl_opts & XDF_WHITESPACE_FLAGS))
-		return a->es->len != b->es->len  || memcmp(ap, bp, a->es->len);
-
-	if (DIFF_XDL_TST(diffopt, IGNORE_WHITESPACE_AT_EOL)) {
-		while (ae > ap && isspace(ae[-1]))
-			ae--;
-		while (be > bp && isspace(be[-1]))
-			be--;
-	}
-
-	while (1) {
-		int ca, cb;
-		ca = next_byte(&ap, &ae, diffopt);
-		cb = next_byte(&bp, &be, diffopt);
-		if (ca != cb)
-			return 1;
-		if (ca < 0)
-			return 0;
-	}
-}
-
-static unsigned get_string_hash(struct emitted_diff_symbol *es, struct diff_options *o)
-{
-	if (o->xdl_opts & XDF_WHITESPACE_FLAGS) {
-		static struct strbuf sb = STRBUF_INIT;
-		const char *ap = es->line, *ae = es->line + es->len;
-		int c;
-
-		strbuf_reset(&sb);
-		while (ae > ap && isspace(ae[-1]))
-			ae--;
-		while ((c = next_byte(&ap, &ae, o)) >= 0)
-			strbuf_addch(&sb, c);
-
-		return memhash(sb.buf, sb.len);
-	} else {
-		return memhash(es->line, es->len);
-	}
+	return !xdiff_compare_lines(a->es->line, a->es->len,
+				    b->es->line, b->es->len,
+				    diffopt->xdl_opts);
 }
 
 static struct moved_entry *prepare_entry(struct diff_options *o,
@@ -797,7 +723,7 @@ static struct moved_entry *prepare_entry(struct diff_options *o,
 	struct moved_entry *ret = xmalloc(sizeof(*ret));
 	struct emitted_diff_symbol *l = &o->emitted_symbols->buf[line_no];
 
-	ret->ent.hash = get_string_hash(l, o);
+	ret->ent.hash = xdiff_hash_string(l->line, l->len, o->xdl_opts);
 	ret->es = l;
 	ret->next_line = NULL;