diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..84c048a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/build/
diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..c4ba431
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,45 @@
+cmake_minimum_required(VERSION 3.27)
+
+project(allcing C)
+
+set(CMAKE_C_STANDARD              23)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+
+# ---- thirdparty modules
+include(CTest)
+
+
+# ---- common config
+add_library(allcing_config INTERFACE)
+target_include_directories(allcing_config
+  INTERFACE
+    ${PROJECT_SOURCE_DIR}
+    ${NF7_GENERATED_DIR}
+)
+target_compile_options(allcing_config INTERFACE
+  $<$<CXX_COMPILER_ID:MSVC>:
+    /W4
+    $<$<CONFIG:Debug>:/WX>
+  >
+  $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:
+    -Wall -Wextra -Wpedantic
+    -Wno-gnu-zero-variadic-macro-arguments
+    $<$<CONFIG:Debug>:-Werror>
+  >
+)
+
+
+# ---- library header
+add_library(allcing INTERFACE)
+target_sources(allcing INTERFACE allcing.h)
+target_link_libraries(allcing INTERFACE allcing_config)
+
+
+# ---- test binary
+if (BUILD_TESTING)
+  add_executable(allcing_test)
+  target_sources(allcing_test PRIVATE test.c)
+  target_link_libraries(allcing_test PRIVATE allcing)
+  add_test(NAME allcing_test COMMAND $<TARGET_FILE:allcing_test>)
+endif()
diff --git a/allcing.h b/allcing.h
new file mode 100644
index 0000000..b9d57df
--- /dev/null
+++ b/allcing.h
@@ -0,0 +1,72 @@
+// No copyright
+#pragma once
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+
+#define ACG_CHUNK_BLOB 0x00
+
+#define ACG_CHUNK_BEGIN 0x01
+#define ACG_CHUNK_END   0x02
+#define ACG_CHUNK_CHECK 0x03
+
+
+static inline uint64_t acg_util_fullbits(uint8_t bits) {
+  return (((uint64_t) 1U) << bits) - 1U;
+}
+static inline uint64_t acg_util_umin(uint64_t a, uint64_t b) {
+  return a > b? b: a;
+}
+
+
+struct acg_stream {
+  uint8_t* buffer;
+  uint64_t size_bytes;
+
+  uint64_t cursor_bits;
+};
+
+static inline bool acg_stream_write_bool(struct acg_stream* s, bool v) {
+  if (s->size_bytes <= s->cursor_bits) {
+    return false;
+  }
+  uint64_t* const c = &s->cursor_bits;
+  s->buffer[*c/8U] |= (!!v) << (*c%8U);
+  ++*c;
+  return true;
+}
+static inline bool acg_stream_write_uint(struct acg_stream* s, uint64_t v, uint8_t unit_bits) {
+  assert(unit_bits >= 2U);
+  assert(unit_bits <= 65U);
+
+  uint8_t*  const buf = s->buffer;
+  uint64_t* const c   = &s->cursor_bits;
+
+  const uint8_t unit_data_bits = unit_bits - 1U;
+  while (v) {
+    const uint64_t next_v = v >> unit_data_bits;
+    acg_stream_write_bool(s, !!next_v);
+
+    const uint8_t frag_bits = acg_util_umin(unit_data_bits, (8U - *c%8U)%8U);
+    if (frag_bits > 0U) {
+      buf[*c/8U] |= (v & acg_util_fullbits(frag_bits)) << (*c%8U);
+      *c += frag_bits;
+    }
+
+    const uint8_t  remain_bits = unit_data_bits - frag_bits;
+    const uint64_t v_part      = (v >> frag_bits) & acg_util_fullbits(remain_bits);
+    memcpy(&buf[*c/8U], &v_part, (remain_bits + 7U) / 8U);
+    *c += remain_bits;
+
+    v = next_v;
+  }
+  return true;
+}
+static inline bool acg_stream_write_int(struct acg_stream* s, int64_t v, uint8_t unit_bits) {
+  assert(unit_bits > 0);
+  const uint64_t uv = v >= 0? ((uint64_t) v): (~((uint64_t) -v) + 1);
+  return acg_stream_write_uint(s, uv, unit_bits);
+}
diff --git a/test.c b/test.c
new file mode 100644
index 0000000..a148d9f
--- /dev/null
+++ b/test.c
@@ -0,0 +1,68 @@
+#include "allcing.h"
+
+#ifdef NDEBUG
+# undef NDEBUG  // this test uses assert() macro
+#endif
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+
+int main(int, char**) {
+# define DEFINE_STREAM(name, offset)  \
+    struct acg_stream s = {  \
+      .buffer     = (uint8_t[1024U]) {0U},  \
+      .size_bytes = 1024U,  \
+      .cursor_bits = (offset),  \
+    }
+# define STREAM(size, offset)  \
+    (struct acg_stream) {  \
+      .buffer = (uint8_t[size]) {0U},  \
+      .size_bytes = (size),  \
+      .cursor_bits = (offset),  \
+    }
+
+  /* acg_stream_write_bool / value=true */ {
+    struct acg_stream s = STREAM(1024U, 0U);
+    assert(acg_stream_write_bool(&s, true));
+    assert(s.buffer[0U] == 0x1U);
+    assert(s.cursor_bits == 1U);
+  }
+  /* acg_stream_write_bool / value=false */ {
+    struct acg_stream s = STREAM(1024U, 0U);
+    assert(acg_stream_write_bool(&s, false));
+    assert(s.buffer[0U] == 0x0U);
+    assert(s.cursor_bits == 1U);
+  }
+
+  /* acg_stream_write_uint / ends in a single byte */ {
+    struct acg_stream s = STREAM(1024U, 0U);
+    assert(acg_stream_write_uint(&s, 7U, 4U));
+    assert(s.buffer[0U] == 0x0EU);
+    assert(s.cursor_bits == 4U);
+  }
+  /* acg_stream_write_uint / ends in a single byte with offset */ {
+    struct acg_stream s = STREAM(1024U, 1U);
+    assert(acg_stream_write_uint(&s, 7U, 4U));
+    assert(s.buffer[0U] == 0x1CU);
+    assert(s.cursor_bits == 5U);
+  }
+  /* acg_stream_write_uint / separated data bits */ {
+    struct acg_stream s = STREAM(1024U, 6U);
+    assert(acg_stream_write_uint(&s, 7U, 4U));
+    assert(s.buffer[0U] == 0x80U);
+    assert(s.buffer[1U] == 0x03U);
+    assert(s.cursor_bits == 10U);
+  }
+  /* acg_stream_write_uint / separated cont flag */ {
+    struct acg_stream s = STREAM(1024U, 7U);
+    assert(acg_stream_write_uint(&s, 7U, 4U));
+    assert(s.buffer[0U] == 0x00U);
+    assert(s.buffer[1U] == 0x07U);
+    assert(s.cursor_bits == 11U);
+  }
+
+  return EXIT_SUCCESS;
+}