From fa2cf40451c328ade606dda129ca691c5e4d6030 Mon Sep 17 00:00:00 2001
From: James Bonfield <jkb@sanger.ac.uk>
Date: Tue, 7 Jul 2026 14:50:06 +0100
Subject: [PATCH] Make gtcheck use a stable sort for "idbl"

Qsort isn't always a stable sort.  Use the array index for ties.
(We could use the pointers themselves, but the struct already contains
an index.)

Fixes a test issue on OpenSolaris, and probably Alpine (although it
looks to have gotten lucky.)

Signed-off-by: James Bonfield <jkb@sanger.ac.uk>
---
 vcfgtcheck.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/vcfgtcheck.c b/vcfgtcheck.c
index 6fae85581..5aa29b7c5 100644
--- a/vcfgtcheck.c
+++ b/vcfgtcheck.c
@@ -827,7 +827,7 @@ static int cmp_idbl(const void *_a, const void *_b)
     idbl_t *b = (idbl_t*)_b;
     if ( a->val < b->val ) return -1;
     if ( a->val > b->val ) return 1;
-    return 0;
+    return a->ism - b->ism; // j^{th}
 }
 static void report_distinctive_sites(args_t *args)
 {