Fix scaling-list storage and V3 flag pointer handling

.github/workflows/test.yml

@@ -14,27 +14,59 @@ jobs:
   linux:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v7
-      - uses: prantlf/setup-v-action@v4
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - uses: prantlf/setup-v-action@92f20bea50d2c9931a28c96bb4997a3c7357baf0 # v4
+        with:
+          version: 0.5.2
       - run: v test .
 
   windows:
     runs-on: windows-2022
     steps:
-      - uses: actions/checkout@v7
-      - uses: prantlf/setup-v-action@v4
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - uses: prantlf/setup-v-action@92f20bea50d2c9931a28c96bb4997a3c7357baf0 # v4
+        with:
+          version: 0.5.2
       - name: Test with the Microsoft C compiler
         run: v -cc msvc test .
 
+  v3:
+    name: Pinned V3 / Linux / TinyCC
+    runs-on: ubuntu-24.04
+    timeout-minutes: 20
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+        with:
+          path: source
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+        with:
+          repository: vlang/v
+          ref: 0dc6a692ed5333cbe3f05ff63ae0766f0333038a
+          path: toolchain/v
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+        with:
+          repository: vlang/vc
+          ref: 8af812feb76c678abd86a8e682fd9ab2790e519c
+          path: toolchain/v/vc
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+        with:
+          repository: vlang/tccbin
+          ref: d6e7ac1b1bcc98aed734a6ecbfa8509f24606c74
+          path: toolchain/v/thirdparty/tcc
+      - run: make -C toolchain/v local=1
+      - run: toolchain/v/v -new-compiler -cc tcc test source
+
   test:
     if: always()
-    needs: [linux, windows]
+    needs: [linux, windows, v3]
     runs-on: ubuntu-24.04
     steps:
       - name: Verify required platforms
         env:
           LINUX_RESULT: ${{ needs.linux.result }}
           WINDOWS_RESULT: ${{ needs.windows.result }}
+          V3_RESULT: ${{ needs.v3.result }}
         run: |
           test "$LINUX_RESULT" = success
           test "$WINDOWS_RESULT" = success
+          test "$V3_RESULT" = success

README.md

@@ -68,3 +68,11 @@ v -cc msvc test .
 They cover fixed-width and Exp-Golomb bit reading, truncated input behavior,
 NAL headers, RBSP look-ahead, integer bit widths, and representative
 High-profile SPS/PPS parsing used by the player.
+
+CI also runs strict V3 with TinyCC on Linux, using a pinned compiler snapshot.
+The regression samples cover custom SPS/PPS scaling lists and the default-list
+flag. Scaling lists are copied explicitly into their fixed storage arrays.
+
+Callers of `Bitstream.read_scaling_list` should pass the flag as `&flag`, not
+`mut &flag`. The pointer itself is not reassigned; only its pointed-to value is
+written. This avoids a pointer-to-pointer mismatch in V3-generated C.

h264.v

@@ -371,7 +371,7 @@ pub fn (mut nal NetworkAbstractionLayerHeader) read_nal_header(mut b Bitstream)
 	nal.type = unsafe { NAL_UNIT_TYPE(b.u(5)) }
 }
 
-pub fn (mut b Bitstream) read_scaling_list(mut scaling_list []i32, size_of_scaling_list i32, mut use_default_scaling_matrix_flag &u32) {
+pub fn (mut b Bitstream) read_scaling_list(mut scaling_list []i32, size_of_scaling_list i32, use_default_scaling_matrix_flag &u32) {
 	mut last_scale := i32(8)
 	mut next_scale := i32(8)
 	mut delta_scale := i32(0)
@@ -577,11 +577,19 @@ pub fn (mut sps SequenceParameterSet) read_sps(mut b Bitstream) {
 				sps.seq_scaling_list_present_flag[i] = b.u1()
 				if sps.seq_scaling_list_present_flag[i] != 0 {
 					if i < 6 {
-						b.read_scaling_list(mut sps.scaling_list_4x4[i][0..], 16, mut
+						mut list := []i32{len: 16}
+						b.read_scaling_list(mut list, 16,
 							&sps.use_default_scaling_matrix_4x4_flag[i])
+						for j in 0 .. 16 {
+							sps.scaling_list_4x4[i][j] = list[j]
+						}
 					} else {
-						b.read_scaling_list(mut sps.scaling_list_8x8[i - 6][0..], 64, mut
+						mut list := []i32{len: 64}
+						b.read_scaling_list(mut list, 64,
 							&sps.use_default_scaling_matrix_8x8_flag[i - 6])
+						for j in 0 .. 64 {
+							sps.scaling_list_8x8[i - 6][j] = list[j]
+						}
 					}
 				}
 			}
@@ -676,12 +684,19 @@ pub fn (mut pps PictureParameterSet) read_pps(mut b Bitstream) {
 				pps.pic_scaling_list_present_flag[i] = b.u1()
 				if pps.pic_scaling_list_present_flag[i] != 0 {
 					if i < 6 {
-						// Make it a slice to get a dynamic array
-						b.read_scaling_list(mut pps.scaling_list_4x4[i][0..], 16, mut
+						mut list := []i32{len: 16}
+						b.read_scaling_list(mut list, 16,
 							&pps.use_default_scaling_matrix_4x4_flag[i])
+						for j in 0 .. 16 {
+							pps.scaling_list_4x4[i][j] = list[j]
+						}
 					} else {
-						b.read_scaling_list(mut pps.scaling_list_8x8[i - 6][0..], 64, mut
+						mut list := []i32{len: 64}
+						b.read_scaling_list(mut list, 64,
 							&pps.use_default_scaling_matrix_8x8_flag[i - 6])
+						for j in 0 .. 64 {
+							pps.scaling_list_8x8[i - 6][j] = list[j]
+						}
 					}
 				}
 			}

h264_test.v

@@ -1,5 +1,50 @@
 module h264
 
+import encoding.hex
+
+fn test_custom_sps_scaling_lists_are_stored() {
+	// FRExt_MMCO4_Sony_B conformance SPS, excluding its NAL header.
+	data :=
+		hex.decode('64001fad9464763b8ac4444a323b1dc5622225191d8ee2b11114222b373669a844566e6cd35088acdcd9a69444cd1b9bc57c9f93f9bf27c9e4e4cd251a4689c9ebe4fd7f27ebe4f5c9a906c694160964')!
+	mut stream := Bitstream{}
+	stream.init(data)
+	mut sps := SequenceParameterSet{}
+	sps.read_sps(mut stream)
+	assert sps.seq_parameter_set_id == 0
+	assert sps.scaling_list_4x4[0][..4] == [i32(6), 12, 12, 19]
+	assert sps.scaling_list_8x8[0][..4] == [i32(6), 10, 10, 13]
+	for i in 0 .. 6 {
+		assert sps.scaling_list_4x4[i][15] != 0
+	}
+	for i in 0 .. 2 {
+		assert sps.scaling_list_8x8[i][63] != 0
+	}
+}
+
+fn test_custom_pps_scaling_list_is_stored() {
+	mut stream := Bitstream{}
+	stream.init(hex.decode('ce3c7fffe0c0')!)
+	mut pps := PictureParameterSet{}
+	pps.read_pps(mut stream)
+	assert pps.pic_scaling_matrix_present_flag == 1
+	for value in pps.scaling_list_4x4[0] {
+		assert value == 8
+	}
+}
+
+fn test_scaling_list_default_flag_points_to_value_not_pointer() {
+	mut stream := Bitstream{}
+	// signed Exp-Golomb -8 makes the first nextScale zero.
+	stream.init([u8(0x08), 0x80])
+	mut list := []i32{len: 16}
+	mut use_default := u32(0)
+	stream.read_scaling_list(mut list, 16, &use_default)
+	assert use_default == 1
+	for value in list {
+		assert value == 8
+	}
+}
+
 fn test_fixed_width_reads_cross_byte_boundaries() {
 	mut stream := Bitstream{}
 	stream.init([u8(0xa5), 0xc0])