[PATCH 1/1] scripts: Changed potential O(n) file size calculation to O(1)

[konrad.schwarz@gmail.com]

The mkemmc.sh script calculates file sizes via `wc -c'.  `wc'
normally works by reading the entire file, resulting in O(n) performance.

Unix file systems obviously know a file's size and POSIX `ls' reports this
information unambiguously, so replacing `wc' with `ls' ensures O(1)
performance.  The files in question tend to be large making this change
worthwhile.

Signed-off-by: Konrad Schwarz <konrad.schwarz@siemens.com>
---
 scripts/mkemmc.sh | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/scripts/mkemmc.sh b/scripts/mkemmc.sh
index 45dc3f08fa..d2c4e84b16 100755
--- a/scripts/mkemmc.sh
+++ b/scripts/mkemmc.sh
@@ -37,13 +37,19 @@ usage() {
     exit "$1"
 }

+file_size() {
+	ls_line=$(ls -Hdog "$1") || return
+	printf %s\\n "$ls_line" | cut -d\  -f3
+	unset ls_line
+}
+
 process_size() {
     name=$1
     image_file=$2
     alignment=$3
     image_arg=$4
     if [ "${image_arg#*:}" = "$image_arg"  ]; then
-        if ! size=$(wc -c < "$image_file" 2>/dev/null); then
+        if ! size=$(file_size "$image_file"); then
             echo "Missing $name image '$image_file'." >&2
             exit 1
         fi
@@ -105,7 +111,7 @@ check_truncation() {
     if [ "$image_file" = "/dev/zero" ]; then
         return
     fi
-    if ! actual_size=$(wc -c < "$image_file" 2>/dev/null); then
+    if ! actual_size=$(file_size "$image_file"); then
         echo "Missing image '$image_file'." >&2
         exit 1
     fi
-- 
2.39.5