update: optimize utility functions

src/core/all_cases/internal/basic_ranges.cc

@@ -63,7 +63,7 @@ void BasicRanges::build() {
     }
 
     std::list<RangesIter> points; // mark ordered interval
-    for (const auto offset : to_offset(BASIC_RANGES_NUM, 0)) {
+    for (const auto offset : BASIC_RANGES_OFFSET) {
         points.emplace_back(ranges.begin() + offset);
     }
     points.emplace_back(ranges.end());
@@ -117,7 +117,7 @@ void BasicRanges::build_async(Executor &&executor, Notifier &&callback) {
         }
 
         auto points = std::make_shared<std::list<RangesIter>>(); // mark ordered interval
-        for (const auto offset : to_offset(BASIC_RANGES_NUM, 0)) {
+        for (const auto offset : BASIC_RANGES_OFFSET) {
             points->emplace_back(ranges.begin() + offset);
         }
         points->emplace_back(ranges.end());

src/core/all_cases/internal/constant.inl

@@ -13,10 +13,10 @@ constexpr auto ALL_CASES_NUM = std::to_array({
     2942906, 2260392, 2942906, 0,
 });
 
-static_assert(ALL_CASES_NUM.size() == 16);
-
 constexpr auto ALL_CASES_NUM_ = array_sum(ALL_CASES_NUM);
 
+constexpr auto ALL_CASES_OFFSET = to_offset(ALL_CASES_NUM);
+
 // ------------------------------------------------------------------------------------- //
 
 constexpr auto BASIC_RANGES_NUM = std::to_array({
@@ -48,10 +48,10 @@ constexpr auto BASIC_RANGES_NUM = std::to_array({
     1260  , 756   , 252   ,
 });
 
-static_assert(BASIC_RANGES_NUM.size() == 203);
-
 constexpr auto BASIC_RANGES_NUM_ = array_sum(BASIC_RANGES_NUM);
 
+constexpr auto BASIC_RANGES_OFFSET = to_offset(BASIC_RANGES_NUM);
+
 // ------------------------------------------------------------------------------------- //
 
 } // namespace klotski::cases

src/core/group/internal/constant/group_union.h

@@ -23,7 +23,7 @@ constexpr auto GROUP_NUM = std::to_array<uint16_t>({
     214, 6  , 18  , 54 , 2   , 44 , 40 , 124 , 84 , 70  , 18  ,
 });
 
-constexpr auto GROUP_OFFSET = to_offset<uint16_t, 203>(GROUP_NUM, 0);
+constexpr auto GROUP_OFFSET = to_offset<uint16_t, 203>(GROUP_NUM);
 
 /// The maximum Group size in each GroupUnion.
 constexpr auto MAX_GROUP_SIZE = std::to_array<uint32_t>({

src/core/short_code/internal/convert.cc

@@ -59,8 +59,8 @@ uint32_t ShortCode::fast_encode(uint64_t common_code) {
 }
 
 uint64_t ShortCode::fast_decode(uint32_t short_code) {
-    auto offset = std::upper_bound(ALL_CASES_OFFSET, ALL_CASES_OFFSET + 16, short_code) - 1;
-    uint64_t head = offset - ALL_CASES_OFFSET;
+    auto offset = std::upper_bound(ALL_CASES_OFFSET.begin(), ALL_CASES_OFFSET.end(), short_code) - 1;
+    uint64_t head = offset - ALL_CASES_OFFSET.begin();
     return (head << 32) | AllCases::instance().fetch()[head][short_code - *offset];
 }
 
@@ -90,11 +90,11 @@ uint32_t ShortCode::tiny_encode(uint64_t common_code) {
 }
 
 uint64_t ShortCode::tiny_decode(uint32_t short_code) { // short code --> common code
-    auto offset = std::upper_bound(ALL_CASES_OFFSET, ALL_CASES_OFFSET + 16, short_code) - 1;
-    auto head = offset - ALL_CASES_OFFSET; // head index
-    short_code -= *offset;
+    auto offset_ = std::upper_bound(ALL_CASES_OFFSET.begin(), ALL_CASES_OFFSET.end(), short_code) - 1;
+    auto head = offset_ - ALL_CASES_OFFSET.begin(); // head index
+    short_code -= *offset_;
 
-    offset = std::upper_bound(RANGE_PREFIX_OFFSET[head], RANGE_PREFIX_OFFSET[head] + 4096, short_code) - 1;
+    auto offset = std::upper_bound(RANGE_PREFIX_OFFSET[head], RANGE_PREFIX_OFFSET[head] + 4096, short_code) - 1;
     auto prefix = offset - RANGE_PREFIX_OFFSET[head]; // range prefix
     short_code -= *offset;
 

src/core/short_code/internal/offset/basic.h

@@ -2,19 +2,16 @@
 
 #include <cstdint>
 
+#include "utils/utility.h"
+#include "all_cases/all_cases.h"
+
 namespace klotski::codec::offset {
 
 /// This is the head index, the offset [0, 29334498) in all cases is obtained
 /// according to the `head` (0 ~ 15). In other words, the short code range can
 /// be obtained according to the position of the 2x2 block.
 
-// TODO: using std::array
-constexpr uint32_t ALL_CASES_OFFSET[16] {
-           0,  2942906,  5203298,  8146204,
-     8146204, 10468254, 12345199, 14667249,
-    14667249, 16989299, 18866244, 21188294,
-    21188294, 24131200, 26391592, 29334498,
-};
+constexpr auto ALL_CASES_OFFSET = to_offset(cases::ALL_CASES_NUM);
 
 /// This is the index for basic ranges, and its position (0 ~ 7311884) in all
 /// basic ranges is located according to the first 12-bit (0 ~ 4095) within the

src/core/utils/utility.h

@@ -23,36 +23,31 @@
 #define KLSK_ASSUME(expr) __builtin_assume(expr)
 
 /// Force function declaration to be inline.
-#define KLSK_INLINE __attribute__((always_inline))
+#define KLSK_INLINE __attribute__ ((always_inline))
 
 namespace klotski {
 
-template <typename T>
-concept Addable = requires(T a, T b) { a + b; };
-
-template <Addable T, size_t N>
+/// Calculate the sum of an array of integers.
+template <typename T, size_t N>
+requires std::is_integral_v<T>
 consteval int array_sum(const std::array<T, N> &arr) {
     return std::accumulate(arr.begin(), arr.end(), 0);
 }
 
-template <Addable T, size_t N>
-consteval std::array<T, N> to_offset(const std::array<T, N> &arr, T base) {
-
-    static_assert(N > 0);
-
+/// Calculate offset list of integer array with sizes.
+template <typename T, size_t N>
+requires std::is_integral_v<T>
+consteval std::array<T, N> to_offset(const std::array<T, N> &arr) {
     std::array<T, N> offset;
-
-    T val = base;
-
+    static_assert(N > 0);
     offset[0] = 0;
 
-    for (int i = 0; i < N - 1; ++i) {
+    T val = 0;
+    for (int i = 0; i < N - 1; ++i) { // TODO: using `std::views::iota`
         val += arr[i];
         offset[i + 1] = val;
     }
-
     return offset;
-
 }
 
 /// Flips the input u32 every two bits in low-high symmetry.