From 6942c4dbb4e7224ea50921a4ee47829ffe5b1dfd Mon Sep 17 00:00:00 2001
From: Elaina Claus <elaina.claus@chtm.me>
Date: Thu, 17 Oct 2024 14:33:22 -0400
Subject: [PATCH] bit smaller of an instruction

---
 src/vbr/vbr.nasm | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/vbr/vbr.nasm b/src/vbr/vbr.nasm
index 729cc1e..26ab1da 100755
--- a/src/vbr/vbr.nasm
+++ b/src/vbr/vbr.nasm
@@ -126,8 +126,8 @@ main:
 
 .check_FAT_size:                     ; we only support a very specific setup of FAT32
     mov bx, fat32_bpb
-    cmp dword [bx + FAT32_bpb_t.sector_count_32], 0      ; SectorsHuge will not be set if FAT12/16
-    ja main.load_stage2
+    test word [bx + FAT32_bpb_t.unused2_ZERO_word], 0      ; TotSectors16 will not be set if FAT32
+    jz main.load_stage2
     ERROR VBR_ERROR_WRONG_FAT_SIZE
 .load_stage2:
     ; read sectors 1-(MAX_STAGE2_BYTES / 512) to stage2 entry point