video: separate repacking code from zimg and make it independent

For whatever purpose. If anything, this makes the zimg wrapper cleaner.

The added tests are not particular exhaustive, but nice to have. This
also makes the scale_zimg.c test pretty useless, because it only tests
repacking (going through the zimg wrapper). In theory, the repack_tests
things could also be used on scalers, but I guess it doesn't matter.

Some things are added over the previous zimg wrapper code. For example,
some fringe formats can now be expanded to 8 bit per component for
convenience.

4 files changed, 442 insertions, 0 deletions

diff --git a/test/ref/repack.txt b/test/ref/repack.txt
new file mode 100644
index 0000000000..3946a6eb47
--- /dev/null
+++ b/test/ref/repack.txt
@@ -0,0 +1,163 @@
+0bgr            => [pa] [un] gbrp            | a=1:1 [tu] [tp]
+0rgb            => [pa] [un] gbrp            | a=1:1 [tu] [tp]
+abgr            => [pa] [un] gbrap           | a=1:1 [tu] [tp]
+argb            => [pa] [un] gbrap           | a=1:1 [tu] [tp]
+ayuv64          => [pa] [un] yuva444p16      | a=1:1 [tu] [tp]
+ayuv64be        => [pa] [un] yuva444p16      | a=1:1 [tu] [tp]
+bayer_bggr16    => no
+bayer_bggr16be  => no
+bayer_bggr8     => no
+bayer_gbrg16    => no
+bayer_gbrg16be  => no
+bayer_gbrg8     => no
+bayer_grbg16    => no
+bayer_grbg16be  => no
+bayer_grbg8     => no
+bayer_rggb16    => no
+bayer_rggb16be  => no
+bayer_rggb8     => no
+bgr0            => [pa] [un] gbrp            | a=1:1 [tu] [tp]
+bgr24           => [pa] [un] gbrp            | a=1:1
+bgr4            => no
+bgr444          => [pa] [un] gbrp4           | a=1:1
+bgr444          => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+bgr444be        => [pa] [un] gbrp4           | a=1:1
+bgr444be        => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+bgr48           => [pa] [un] gbrp16          | a=1:1
+bgr48be         => [pa] [un] gbrp16          | a=1:1
+bgr4_byte       => [pa] [un] gbrp2           | a=1:1
+bgr4_byte       => [pa] [un] gbrp1           | a=1:1 [round-down]
+bgr4_byte       => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+bgr555          => [pa] [un] gbrp5           | a=1:1
+bgr555          => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+bgr555be        => [pa] [un] gbrp5           | a=1:1
+bgr555be        => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+bgr565          => [pa] [un] gbrp6           | a=1:1
+bgr565          => [pa] [un] gbrp5           | a=1:1 [round-down]
+bgr565          => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+bgr565be        => [pa] [un] gbrp6           | a=1:1
+bgr565be        => [pa] [un] gbrp5           | a=1:1 [round-down]
+bgr565be        => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+bgr8            => [pa] [un] gbrp3           | a=1:1
+bgr8            => [pa] [un] gbrp2           | a=1:1 [round-down]
+bgr8            => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+bgra            => [pa] [un] gbrap           | a=1:1 [tu] [tp]
+bgra64          => [pa] [un] gbrap16         | a=1:1
+bgra64be        => [pa] [un] gbrap16         | a=1:1
+cuda            => no
+d3d11           => no
+d3d11va_vld     => no
+drm_prime       => no
+dxva2_vld       => no
+gbrap10be       => [pa] [un] gbrap10         | a=1:1
+gbrap12be       => [pa] [un] gbrap12         | a=1:1
+gbrap16be       => [pa] [un] gbrap16         | a=1:1
+gbrapf32be      => [pa] [un] gbrapf32        | a=1:1
+gbrp10be        => [pa] [un] gbrp10          | a=1:1
+gbrp12be        => [pa] [un] gbrp12          | a=1:1
+gbrp14be        => [pa] [un] gbrp14          | a=1:1
+gbrp16be        => [pa] [un] gbrp16          | a=1:1
+gbrp9be         => [pa] [un] gbrp9           | a=1:1
+gbrpf32be       => [pa] [un] gbrpf32         | a=1:1
+gray10be        => [pa] [un] gray10          | a=1:1
+gray12be        => [pa] [un] gray12          | a=1:1
+gray14be        => [pa] [un] gray14          | a=1:1
+gray16be        => [pa] [un] gray16          | a=1:1
+gray9be         => [pa] [un] gray9           | a=1:1
+grayf32be       => [pa] [un] grayf32         | a=1:1
+mediacodec      => no
+mmal            => no
+monob           => [pa] [un] y1              | a=8:1 [tu] [tp]
+monob           => [pa] [un] gray            | a=8:1 [expand-8bit]
+monow           => [pa] [un] y1              | a=8:1 [tu] [tp]
+monow           => [pa] [un] gray            | a=8:1 [expand-8bit]
+nv12            => [pa] [un] yuv420p         | a=2:2 [tu] [tp]
+nv16            => [pa] [un] yuv422p         | a=2:1
+nv20            => [pa] [un] yuv422p10       | a=2:1
+nv20be          => [pa] [un] yuv422p10       | a=2:1
+nv21            => [pa] [un] yuv420p         | a=2:2 [tu] [tp]
+nv24            => [pa] [un] yuv444p         | a=1:1
+nv42            => [pa] [un] yuv444p         | a=1:1
+opencl          => no
+p010            => [pa] [un] yuv420p16       | a=2:2
+p010be          => [pa] [un] yuv420p16       | a=2:2
+p016            => [pa] [un] yuv420p16       | a=2:2
+p016be          => [pa] [un] yuv420p16       | a=2:2
+pal8            =>      [un] gbrap           | a=1:1
+qsv             => no
+rgb0            => [pa] [un] gbrp            | a=1:1 [tu] [tp]
+rgb24           => [pa] [un] gbrp            | a=1:1
+rgb30           => [pa] [un] gbrp10          | a=1:1
+rgb4            => no
+rgb444          => [pa] [un] gbrp4           | a=1:1
+rgb444          => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+rgb444be        => [pa] [un] gbrp4           | a=1:1
+rgb444be        => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+rgb48           => [pa] [un] gbrp16          | a=1:1
+rgb48be         => [pa] [un] gbrp16          | a=1:1 [tu] [tp]
+rgb4_byte       => [pa] [un] gbrp2           | a=1:1
+rgb4_byte       => [pa] [un] gbrp1           | a=1:1 [round-down]
+rgb4_byte       => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+rgb555          => [pa] [un] gbrp5           | a=1:1
+rgb555          => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+rgb555be        => [pa] [un] gbrp5           | a=1:1
+rgb555be        => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+rgb565          => [pa] [un] gbrp6           | a=1:1
+rgb565          => [pa] [un] gbrp5           | a=1:1 [round-down]
+rgb565          => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+rgb565be        => [pa] [un] gbrp6           | a=1:1
+rgb565be        => [pa] [un] gbrp5           | a=1:1 [round-down]
+rgb565be        => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+rgb8            => [pa] [un] gbrp3           | a=1:1
+rgb8            => [pa] [un] gbrp2           | a=1:1 [round-down]
+rgb8            => [pa] [un] gbrp            | a=1:1 [expand-8bit]
+rgba            => [pa] [un] gbrap           | a=1:1 [tu] [tp]
+rgba64          => [pa] [un] gbrap16         | a=1:1 [tu] [tp]
+rgba64be        => [pa] [un] gbrap16         | a=1:1
+uyvy422         => [pa] [un] yuv422p         | a=2:1
+uyyvyy411       => no
+vaapi           => no
+vaapi_idct      => no
+vaapi_moco      => no
+vdpau           => no
+vdpau_output    => no
+videotoolbox    => no
+vulkan          => no
+xvmc            => no
+xyz12           => [pa] [un] gbrp16          | a=1:1
+xyz12be         => [pa] [un] gbrp16          | a=1:1
+y210            => [pa] [un] yuv422p16       | a=2:1
+y210be          => [pa] [un] yuv422p16       | a=2:1
+ya16            => [pa] [un] yap16           | a=1:1 [tu] [tp]
+ya16be          => [pa] [un] yap16           | a=1:1
+ya8             => [pa] [un] yap8            | a=1:1
+yuv420p10be     => [pa] [un] yuv420p10       | a=2:2
+yuv420p12be     => [pa] [un] yuv420p12       | a=2:2
+yuv420p14be     => [pa] [un] yuv420p14       | a=2:2
+yuv420p16be     => [pa] [un] yuv420p16       | a=2:2
+yuv420p9be      => [pa] [un] yuv420p9        | a=2:2
+yuv422p10be     => [pa] [un] yuv422p10       | a=2:1
+yuv422p12be     => [pa] [un] yuv422p12       | a=2:1
+yuv422p14be     => [pa] [un] yuv422p14       | a=2:1
+yuv422p16be     => [pa] [un] yuv422p16       | a=2:1 [tu] [tp]
+yuv422p9be      => [pa] [un] yuv422p9        | a=2:1
+yuv440p10be     => [pa] [un] yuv440p10       | a=1:2
+yuv440p12be     => [pa] [un] yuv440p12       | a=1:2
+yuv444p10be     => [pa] [un] yuv444p10       | a=1:1
+yuv444p12be     => [pa] [un] yuv444p12       | a=1:1
+yuv444p14be     => [pa] [un] yuv444p14       | a=1:1
+yuv444p16be     => [pa] [un] yuv444p16       | a=1:1
+yuv444p9be      => [pa] [un] yuv444p9        | a=1:1
+yuva420p10be    => [pa] [un] yuva420p10      | a=2:2
+yuva420p16be    => [pa] [un] yuva420p16      | a=2:2
+yuva420p9be     => [pa] [un] yuva420p9       | a=2:2
+yuva422p10be    => [pa] [un] yuva422p10      | a=2:1
+yuva422p12be    => [pa] [un] yuva422p12      | a=2:1
+yuva422p16be    => [pa] [un] yuva422p16      | a=2:1
+yuva422p9be     => [pa] [un] yuva422p9       | a=2:1
+yuva444p10be    => [pa] [un] yuva444p10      | a=1:1
+yuva444p12be    => [pa] [un] yuva444p12      | a=1:1
+yuva444p16be    => [pa] [un] yuva444p16      | a=1:1
+yuva444p9be     => [pa] [un] yuva444p9       | a=1:1
+yuyv422         => [pa] [un] yuv422p         | a=2:1
+yvyu422         => [pa] [un] yuv422p         | a=2:1 [tu] [tp]
diff --git a/test/repack.c b/test/repack.c
new file mode 100644
index 0000000000..ede6046350
--- /dev/null
+++ b/test/repack.c
@@ -0,0 +1,249 @@
+#include <libavutil/pixfmt.h>
+
+#include "common/common.h"
+#include "tests.h"
+#include "video/fmt-conversion.h"
+#include "video/img_format.h"
+#include "video/repack.h"
+#include "video/zimg.h"
+
+// Excuse the utter stupidity.
+#define UNFUCK(v) ((v) > 0 ? (v) : pixfmt2imgfmt(-(v)))
+static_assert(IMGFMT_START > 0, "");
+#define IMGFMT_GBRP (-AV_PIX_FMT_GBRP)
+#define IMGFMT_GBRAP (-AV_PIX_FMT_GBRAP)
+
+struct entry {
+    int w, h;
+    int fmt_a;
+    const void *const a[4];
+    int fmt_b;
+    const void *const b[4];
+    int flags;
+};
+
+#define P8(...) (const uint8_t[]){__VA_ARGS__}
+#define P16(...) (const uint16_t[]){__VA_ARGS__}
+
+// Warning: only entries that match existing conversions are tested.
+static const struct entry repack_tests[] = {
+    // Note: the '0' tests rely on 0 being written, although by definition the
+    //       contents of this padding is undefined. The repacker always writes
+    //       it this way, though.
+    {1, 1, IMGFMT_RGB0,             {P8(1, 2, 3, 0)},
+           IMGFMT_GBRP,             {P8(2), P8(3), P8(1)}},
+    {1, 1, IMGFMT_BGR0,             {P8(1, 2, 3, 0)},
+           IMGFMT_GBRP,             {P8(2), P8(1), P8(3)}},
+    {1, 1, IMGFMT_0RGB,             {P8(0, 1, 2, 3)},
+           IMGFMT_GBRP,             {P8(2), P8(3), P8(1)}},
+    {1, 1, IMGFMT_0BGR,             {P8(0, 1, 2, 3)},
+           IMGFMT_GBRP,             {P8(2), P8(1), P8(3)}},
+    {1, 1, IMGFMT_RGBA,             {P8(1, 2, 3, 4)},
+           IMGFMT_GBRAP,            {P8(2), P8(3), P8(1), P8(4)}},
+    {1, 1, IMGFMT_BGRA,             {P8(1, 2, 3, 4)},
+           IMGFMT_GBRAP,            {P8(2), P8(1), P8(3), P8(4)}},
+    {1, 1, IMGFMT_ARGB,             {P8(4, 1, 2, 3)},
+           IMGFMT_GBRAP,            {P8(2), P8(3), P8(1), P8(4)}},
+    {1, 1, IMGFMT_ABGR,             {P8(4, 1, 2, 3)},
+           IMGFMT_GBRAP,            {P8(2), P8(1), P8(3), P8(4)}},
+    {1, 1, IMGFMT_RGBA64,           {P16(0x1a1b, 0x2a2b, 0x3a3b, 0x4a4b)},
+           -AV_PIX_FMT_GBRAP16,     {P16(0x2a2b), P16(0x3a3b),
+                                     P16(0x1a1b), P16(0x4a4b)}},
+    {1, 1, -AV_PIX_FMT_RGB48BE,     {P16(0x1a1b, 0x2a2b, 0x3a3b)},
+           -AV_PIX_FMT_GBRP16,      {P16(0x2b2a), P16(0x3b3a),
+                                     P16(0x1b1a)}},
+    {8, 1, -AV_PIX_FMT_MONOWHITE,   {P8(0xAA)},
+           IMGFMT_Y1,               {P8(0, 1, 0, 1, 0, 1, 0, 1)}},
+    {8, 1, -AV_PIX_FMT_MONOBLACK,   {P8(0xAA)},
+           IMGFMT_Y1,               {P8(1, 0, 1, 0, 1, 0, 1, 0)}},
+    {2, 2, IMGFMT_NV12,             {P8(1, 2, 3, 4), P8(5, 6)},
+           IMGFMT_420P,             {P8(1, 2, 3, 4), P8(5), P8(6)}},
+    {2, 2, -AV_PIX_FMT_NV21,        {P8(1, 2, 3, 4), P8(5, 6)},
+           IMGFMT_420P,             {P8(1, 2, 3, 4), P8(6), P8(5)}},
+    {1, 1, -AV_PIX_FMT_AYUV64,      {P16(1, 2, 3, 4)},
+           -AV_PIX_FMT_YUVA444P16,  {P16(2), P16(3), P16(4), P16(1)}},
+    {1, 1, -AV_PIX_FMT_AYUV64BE,    {P16(0x0100, 0x0200, 0x0300, 0x0400)},
+           -AV_PIX_FMT_YUVA444P16,  {P16(2), P16(3), P16(4), P16(1)}},
+    {2, 1, -AV_PIX_FMT_YVYU422,     {P8(1, 2, 3, 4)},
+           -AV_PIX_FMT_YUV422P,     {P8(1, 3), P8(4), P8(2)}},
+    {1, 1, -AV_PIX_FMT_YA16,        {P16(1, 2)},
+           IMGFMT_YAP16,            {P16(1), P16(2)}},
+    {2, 1, -AV_PIX_FMT_YUV422P16BE, {P16(0x1a1b, 0x2a2b), P16(0x3a3b),
+                                     P16(0x4a4b)},
+           -AV_PIX_FMT_YUV422P16,   {P16(0x1b1a, 0x2b2a), P16(0x3b3a),
+                                     P16(0x4b4a)}},
+};
+
+static bool is_true_planar(int imgfmt)
+{
+    struct mp_regular_imgfmt desc;
+    if (!mp_get_regular_imgfmt(&desc, imgfmt))
+        return false;
+
+    for (int n = 0; n < desc.num_planes; n++) {
+        if (desc.planes[n].num_components != 1)
+            return false;
+    }
+
+    return true;
+}
+
+static int try_repack(struct test_ctx *ctx, FILE *f, int imgfmt, int flags,
+                      int not_if_fmt)
+{
+    char *head = mp_tprintf(80, "%-15s =>", mp_imgfmt_to_name(imgfmt));
+    struct mp_repack *un = mp_repack_create_planar(imgfmt, false, flags);
+    struct mp_repack *pa = mp_repack_create_planar(imgfmt, true, flags);
+
+    // If both exists, they must be always symmetric.
+    if (un && pa) {
+        assert(mp_repack_get_format_src(pa) == mp_repack_get_format_dst(un));
+        assert(mp_repack_get_format_src(un) == mp_repack_get_format_dst(pa));
+        assert(mp_repack_get_align_x(pa) == mp_repack_get_align_x(un));
+        assert(mp_repack_get_align_y(pa) == mp_repack_get_align_y(un));
+    }
+
+    int a = 0;
+    int b = 0;
+    if (un) {
+        a = mp_repack_get_format_src(un);
+        b = mp_repack_get_format_dst(un);
+    } else if (pa) {
+        a = mp_repack_get_format_dst(pa);
+        b = mp_repack_get_format_src(pa);
+    }
+
+    // Skip the identity ones because they're uninteresting, and add too much
+    // noise. But still make sure they behave as expected.
+    if (is_true_planar(imgfmt)) {
+        // (note that we require alpha-enabled zimg)
+        assert(mp_zimg_supports_in_format(imgfmt));
+        assert(un && pa);
+        assert(a == imgfmt && b == imgfmt);
+        talloc_free(pa);
+        talloc_free(un);
+        return 0;
+    }
+
+    struct mp_repack *rp = pa ? pa : un;
+    if (!rp) {
+        if (!flags)
+            fprintf(f, "%s no\n", head);
+        return 0;
+    }
+
+    assert(a == imgfmt);
+    if (b && b == not_if_fmt) {
+        talloc_free(pa);
+        talloc_free(un);
+        return 0;
+    }
+
+    fprintf(f, "%s %4s %4s %-15s |", head, pa ? "[pa]" : "", un ? "[un]" : "",
+            mp_imgfmt_to_name(b));
+
+    fprintf(f, " a=%d:%d", mp_repack_get_align_x(rp), mp_repack_get_align_y(rp));
+
+    if (flags & REPACK_CREATE_ROUND_DOWN)
+        fprintf(f, " [round-down]");
+    if (flags & REPACK_CREATE_EXPAND_8BIT)
+        fprintf(f, " [expand-8bit]");
+
+    // LCM of alignment of all packers.
+    int ax = mp_repack_get_align_x(rp);
+    int ay = mp_repack_get_align_y(rp);
+    if (pa && un) {
+        ax = MPMAX(mp_repack_get_align_x(pa), mp_repack_get_align_x(un));
+        ay = MPMAX(mp_repack_get_align_y(pa), mp_repack_get_align_y(un));
+    }
+
+    for (int n = 0; n < MP_ARRAY_SIZE(repack_tests); n++) {
+        const struct entry *e = &repack_tests[n];
+        int fmt_a = UNFUCK(e->fmt_a);
+        int fmt_b = UNFUCK(e->fmt_b);
+        if (!(fmt_a == a && fmt_b == b && e->flags == flags))
+            continue;
+
+        // We convert a "random" macro pixel to catch potential addressing bugs
+        // that might be ignored with (0, 0) origins.
+        struct mp_image *ia = mp_image_alloc(fmt_a, e->w * 5 * ax, e->h * 5 * ay);
+        struct mp_image *ib = mp_image_alloc(fmt_b, e->w * 7 * ax, e->h * 6 * ay);
+        int sx = 4 * ax, sy = 3 * ay, dx = 3 * ax, dy = 2 * ay;
+
+        assert(ia && ib);
+
+        for (int pack = 0; pack < 2; pack++) {
+            struct mp_repack *repacker = pack ? pa : un;
+            if (!repacker)
+                continue;
+
+            mp_image_clear(ia, 0, 0, ia->w, ia->h);
+            mp_image_clear(ib, 0, 0, ib->w, ib->h);
+
+            const void *const *dstd = pack ? e->a : e->b;
+            const void *const *srcd = pack ? e->b : e->a;
+            struct mp_image *dsti = pack ? ia : ib;
+            struct mp_image *srci = pack ? ib : ia;
+
+            bool r = repack_config_buffers(repacker, 0, dsti, 0, srci, NULL);
+            assert(r);
+
+            for (int p = 0; p < srci->num_planes; p++) {
+                uint8_t *ptr = mp_image_pixel_ptr(srci, p, sx, sy);
+                for (int y = 0; y < e->h >> srci->fmt.ys[p]; y++) {
+                    int w = e->w >> srci->fmt.xs[p];
+                    int wb = (w * srci->fmt.bpp[p] + 7) / 8;
+                    const void *cptr = (uint8_t *)srcd[p] + wb * y;
+                    memcpy(ptr + srci->stride[p] * y, cptr, wb);
+                }
+            }
+
+            repack_line(repacker, dx, dy, sx, sy, e->w);
+
+            for (int p = 0; p < dsti->num_planes; p++) {
+                uint8_t *ptr = mp_image_pixel_ptr(dsti, p, dx, dy);
+                for (int y = 0; y < e->h >> dsti->fmt.ys[p]; y++) {
+                    int w = e->w >> dsti->fmt.xs[p];
+                    int wb = (w * dsti->fmt.bpp[p] + 7) / 8;
+                    const void *cptr = (uint8_t *)dstd[p] + wb * y;
+                    assert_memcmp(ptr + dsti->stride[p] * y, cptr, wb);
+                }
+            }
+
+            fprintf(f, " [t%s]", pack ? "p" : "u");
+        }
+
+        talloc_free(ia);
+        talloc_free(ib);
+    }
+
+    fprintf(f, "\n");
+
+    talloc_free(pa);
+    talloc_free(un);
+    return b;
+}
+
+static void run(struct test_ctx *ctx)
+{
+    FILE *f = test_open_out(ctx, "repack.txt");
+
+    init_imgfmts_list();
+    for (int n = 0; n < num_imgfmts; n++) {
+        int imgfmt = imgfmts[n];
+
+        int other = try_repack(ctx, f, imgfmt, 0, 0);
+        try_repack(ctx, f, imgfmt, REPACK_CREATE_ROUND_DOWN, other);
+        try_repack(ctx, f, imgfmt, REPACK_CREATE_EXPAND_8BIT, other);
+    }
+
+    fclose(f);
+
+    assert_text_files_equal(ctx, "repack.txt", "repack.txt",
+                "This can fail if FFmpeg/libswscale adds or removes pixfmts.");
+}
+
+const struct unittest test_repack = {
+    .name = "repack",
+    .run = run,
+};
diff --git a/test/tests.c b/test/tests.c
index 9ef88f4a8d..d8df43f319 100644
--- a/test/tests.c
+++ b/test/tests.c
@@ -12,6 +12,7 @@ static const struct unittest *unittests[] = {
     &test_paths,
     &test_repack_sws,
 #if HAVE_ZIMG
+    &test_repack, // zimg only due to cross-checking with zimg.c
     &test_repack_zimg,
 #endif
     NULL
@@ -128,3 +129,25 @@ void assert_text_files_equal_impl(const char *file, int line,
         abort();
     }
 }
+
+static void hexdump(const uint8_t *d, size_t size)
+{
+    printf("|");
+    while (size--) {
+        printf(" %02x", d[0]);
+        d++;
+    }
+    printf(" |\n");
+}
+
+void assert_memcmp_impl(const char *file, int line,
+                        const void *a, const void *b, size_t size)
+{
+    if (memcmp(a, b, size) == 0)
+        return;
+
+    printf("%s:%d: mismatching data:\n", file, line);
+    hexdump(a, size);
+    hexdump(b, size);
+    abort();
+}
diff --git a/test/tests.h b/test/tests.h
index f4065f596f..8b2eb98174 100644
--- a/test/tests.h
+++ b/test/tests.h
@@ -43,6 +43,7 @@ extern const struct unittest test_json;
 extern const struct unittest test_linked_list;
 extern const struct unittest test_repack_sws;
 extern const struct unittest test_repack_zimg;
+extern const struct unittest test_repack;
 extern const struct unittest test_paths;
 
 #define assert_true(x) assert(x)
@@ -54,6 +55,10 @@ extern const struct unittest test_paths;
 #define assert_float_equal(a, b, tolerance) \
     assert_float_equal_impl(__FILE__, __LINE__, (a), (b), (tolerance))
 
+// Assert that memcmp(a,b,s)==0, or hexdump output on failure.
+#define assert_memcmp(a, b, s) \
+    assert_memcmp_impl(__FILE__, __LINE__, (a), (b), (s))
+
 // Require that the files "ref" and "new" are the same. The paths can be
 // relative to ref_path and out_path respectively. If they're not the same,
 // the output of "diff" is shown, the err message (if not NULL), and the test
@@ -69,6 +74,8 @@ void assert_float_equal_impl(const char *file, int line,
 void assert_text_files_equal_impl(const char *file, int line,
                                   struct test_ctx *ctx, const char *ref,
                                   const char *new, const char *err);
+void assert_memcmp_impl(const char *file, int line,
+                        const void *a, const void *b, size_t size);
 
 // Open a new file in the out_path. Always succeeds.
 FILE *test_open_out(struct test_ctx *ctx, const char *name);