Re: trim_common_tail bug?

[Jeff King <peff@peff.net>]

On Sat, Dec 15, 2007 at 03:02:02PM -0500, Jeff King wrote:

> >   	for (i = 0, recovered = 0; recovered < trimmed && i <= ctx; i++) {
> > 		while (recovered < trimmed && ap[recovered++] != '\n')
> > 	        	; /* nothing */
> > 	}
> > 
> > then (warning: I haven't had my coffee yet)?
> 
> Yes, I think that is equivalent. My sleep-deprived brain keeps thinking
> there must be a more clear way of writing this whole loop, but it
> escapes me at the moment.

And this came to me in a dream. :) It fixes the bug, and I think it is a
bit simpler to see the termination conditions in a single loop. But
please double-check correctness, and that you agree that it is more
readable.

---
diff --git a/xdiff-interface.c b/xdiff-interface.c
index 700def2..98b02ed 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -110,7 +110,7 @@ int xdiff_outf(void *priv_, mmbuffer_t *mb, int nbuf)
 static void trim_common_tail(mmfile_t *a, mmfile_t *b, long ctx)
 {
 	const int blk = 1024;
-	long trimmed = 0, recovered = 0, i;
+	long trimmed = 0, recovered = 0;
 	char *ap = a->ptr + a->size;
 	char *bp = b->ptr + b->size;
 	long smaller = (a->size < b->size) ? a->size : b->size;
@@ -121,10 +121,9 @@ static void trim_common_tail(mmfile_t *a, mmfile_t *b, long ctx)
 		bp -= blk;
 	}
 
-	for (i = 0, recovered = 0; recovered < trimmed && i <= ctx; i++) {
-		while (recovered < trimmed && ap[recovered] != '\n')
-			recovered++;
-	}
+	while (recovered < trimmed && ctx)
+		if (ap[recovered++] == '\n')
+			ctx--;
 	a->size -= (trimmed - recovered);
 	b->size -= (trimmed - recovered);
 }