From d4f85d01bdf7301d5f7a2c4e51c3a84024561b26 Mon Sep 17 00:00:00 2001
From: Robert de Bath <rdebath@tvisiontech.co.uk>
Date: Sun, 3 Sep 2023 18:39:17 -1000
Subject: [PATCH] DISK: Fix VHD to Ensure that the CHS capacity exceeds the
 disk length

If the total sectors exceeds 127Gb this is not possible, but normal
simh disks are smaller and the largest user settable size via RAUSER
is just under 1Tb.  The excessive size case (>127Gb) will have a CHS
of 0xFFFF10FF.

simh never cares about the CHS Disk Geometry value in the VHD footer
data structure, but other applications which do care about the CHS
value using the previously incorrect value as the capacity of the disk
even though the Current Size indicated in the footer may have been
larger.
---
 sim_disk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sim_disk.c b/sim_disk.c
index 4b9d0dfa..f0bc3264 100644
--- a/sim_disk.c
+++ b/sim_disk.c
@@ -5758,7 +5758,7 @@ if (1) { /* CHS Calculation */
             cylinderTimesHeads = totalSectors / sectorsPerTrack;
             }
         }
-    cylinders = cylinderTimesHeads / heads;
+    cylinders = (totalSectors + sectorsPerTrack * heads - 1) / (sectorsPerTrack * heads);
     Footer.DiskGeometry = NtoHl ((cylinders<<16)|(heads<<8)|sectorsPerTrack);
     }
 Footer.Checksum = NtoHl (CalculateVhdFooterChecksum(&Footer, sizeof(Footer)));