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ref: b61ca21ef5e741a68439c84e9f8c79f690215375
parent: 14806f5a6b9c28df86a14e726260520c733faa17
author: Ori Bernstein <ori@eigenstate.org>
date: Sun Feb 12 17:56:13 EST 2023

merge3: align edges of chunks

--- a/merge3.c
+++ b/merge3.c
@@ -63,7 +63,7 @@
 char*
 merge(Diff *l, Diff *r)
 {
-	int il, ir, a, b;
+	int il, ir, a, b, δ;
 	Change *lc, *rc;
 	vlong ln;
 
@@ -78,10 +78,33 @@
 		if(il < l->nchanges)
 			lc = &l->changes[il];
 		if(ir < r->nchanges)
-			rc = &r->changes[il];
+			rc = &r->changes[ir];
 		if(overlaps(lc, rc)){
-			a = (lc->a < rc->a) ? lc->a : rc->a;
-			b = (lc->b > rc->b) ? lc->b : rc->b;
+			/*
+			 * align the edges of the chunks
+			 */
+			if(lc->a < rc->a){
+				a = lc->a;
+				δ = rc->a - lc->a;
+				rc->a -= δ;
+				rc->c -= δ;
+			}else{
+				a = rc->a;
+				δ = lc->a - rc->a;
+				lc->a -= δ;
+				lc->c -= δ;
+			}
+			if(lc->b > rc->b){
+				b = lc->b;
+				δ = lc->b - rc->b;
+				rc->b += δ;
+				rc->d += δ;
+			}else{
+				b = rc->b;
+				δ = rc->b - lc->b;
+				rc->b += δ;
+				rc->d += δ;
+			}
 			fetch(l, l->ixold, ln, a-1, l->input[0], "");
 			Bprint(&stdout, "<<<<<<<<<< %s\n", l->file2);
 			fetch(l, l->ixnew, lc->c, lc->d, l->input[1], "");