From 07c38b27df7b488b8724882b996d17d7086d2662 Mon Sep 17 00:00:00 2001
From: "Gabriel A. Devenyi" <gdevenyi@gmail.com>
Date: Fri, 14 Aug 2026 20:52:31 -0400
Subject: [PATCH] BUG: Compare NIfTI test output by content, not by compressed
 bytes

nifti_c22_copy_image has been failing on this machine since before any of
this work started.  It converts an image i16 -> i64 -> i16 and asserts
the result matches the original, using

    cmp out.c22.0.i16.nii.gz out.c22.2.0.i16.nii.gz

That compares gzip output, which is not reproducible across zlib
implementations.  The system zlib here is zlib-ng 1.3.1, which Arch,
CachyOS and a growing number of distributions ship in place of stock
zlib; it encodes the same input differently.  Both files come out at
exactly 642454 bytes and differ from byte 321594 on.

The conversion itself is fine.  Decompressed, the two files are
byte-identical at 1114768 bytes each, so the round-trip through int64 and
back preserves the data exactly, which is what the test set out to check.
Confirmed the other way too: in an Ubuntu 24.04 container with stock
zlib 1.3, the test passes unmodified.

The test now decompresses before comparing, via a small nii_cmp helper
that falls back to plain cmp for uncompressed files.  With this the suite
is 92 of 92 on both zlib-ng and stock zlib; previously it was 91 of 92
on any zlib-ng system.

(cherry picked from commit 7d92f16249b7545db8e0f22bedb0da767e7af75e)
---
 .../cmake_testscripts/c22_copy_image.sh       | 21 +++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/nifti2/nifti_regress_test/cmake_testscripts/c22_copy_image.sh b/nifti2/nifti_regress_test/cmake_testscripts/c22_copy_image.sh
index a3abddc2..18c435c9 100644
--- a/nifti2/nifti_regress_test/cmake_testscripts/c22_copy_image.sh
+++ b/nifti2/nifti_regress_test/cmake_testscripts/c22_copy_image.sh
@@ -11,6 +11,23 @@ DATA=$2
 OUT_DATA=$(dirname ${DATA}) #Need to write to separate directory
 cd ${OUT_DATA}
 
+
+# Compare two NIfTI files by content rather than by compressed bytes.
+#
+# gzip output is not reproducible across zlib implementations: zlib-ng,
+# which Arch, CachyOS and other current distributions ship as the system
+# zlib, encodes the same input differently from stock zlib.  Comparing
+# the .gz files directly therefore fails on those systems even though the
+# image data round-trips perfectly.  Decompress first and compare that.
+nii_cmp() {
+    if [ "${1##*.}" = "gz" ]; then
+        gzip -dc "$1" > "$1.raw" && gzip -dc "$2" > "$2.raw" || return 1
+        cmp "$1.raw" "$2.raw"
+        return $?
+    fi
+    cmp "$1" "$2"
+}
+
 # note the main input file and prefix for all output files
 infile=$DATA/e4.60005.nii.gz
 prefix=out.c22
@@ -42,7 +59,7 @@ ${NT} -copy_image -infile ${prefix}.0.i16.nii.gz \
 ${NT} -copy_image -infile ${prefix}.1.i64.nii.gz   \
                   -prefix ${prefix}.2.0.i16.nii.gz \
                   -convert2dtype NIFTI_TYPE_INT16 -convert_verify
-if cmp ${prefix}.0.i16.nii.gz ${prefix}.2.0.i16.nii.gz
+if nii_cmp ${prefix}.0.i16.nii.gz ${prefix}.2.0.i16.nii.gz
 then
 echo ""
 else
@@ -57,7 +74,7 @@ ${NT} -cbl -infile ${prefix}.0.i16.nii.gz \
 ${NT} -copy_image -infile ${prefix}.1.f32.nii.gz   \
                   -prefix ${prefix}.2.1.i16.nii.gz \
                   -convert2dtype NIFTI_TYPE_INT16 -convert_fail_choice warn
-if cmp ${prefix}.0.i16.nii.gz ${prefix}.2.1.i16.nii.gz
+if nii_cmp ${prefix}.0.i16.nii.gz ${prefix}.2.1.i16.nii.gz
 then
 echo ""
 else