hakmem/core/box/smallsegment_v5_box.h

// smallsegment_v5_box.h - SmallSegment v5（Phase v5-0）
//
// 2MiB Segment / 64KiB Page ベースの O(1) page_meta lookup

#ifndef HAKMEM_SMALLSEGMENT_V5_BOX_H
#define HAKMEM_SMALLSEGMENT_V5_BOX_H

#include <stdint.h>
#include "smallobject_hotbox_v5_box.h"

#define SMALL_SEGMENT_V5_SIZE       (2 * 1024 * 1024)    // 2 MiB
#define SMALL_SEGMENT_V5_PAGE_SIZE  (64 * 1024)          // 64 KiB
#define SMALL_SEGMENT_V5_NUM_PAGES  (SMALL_SEGMENT_V5_SIZE / SMALL_SEGMENT_V5_PAGE_SIZE)  // 32
#define SMALL_SEGMENT_V5_MAGIC      0xDEADBEEF
#define SMALL_SEGMENT_V5_PAGE_SHIFT 16                   // log2(64KiB)

// ポインタマクロ - O(1) segment/page 計算

// SMALL_SEGMENT_V5_BASE_FROM_PTR(ptr) - ptr から segment base を mask で計算
#define SMALL_SEGMENT_V5_BASE_FROM_PTR(ptr) \
    ((SmallSegmentV5*)((uintptr_t)(ptr) & ~(SMALL_SEGMENT_V5_SIZE - 1)))

// SMALL_SEGMENT_V5_PAGE_IDX(seg, ptr) - segment 内の page_idx を shift で計算
#define SMALL_SEGMENT_V5_PAGE_IDX(seg, ptr) \
    (((uintptr_t)(ptr) - (uintptr_t)(seg)->base) >> SMALL_SEGMENT_V5_PAGE_SHIFT)

// SMALL_SEGMENT_V5_PAGE_META(seg, ptr) - page_meta への O(1) access（bounds check付き）
#define SMALL_SEGMENT_V5_PAGE_META(seg, ptr) \
    ({  \
        SmallSegmentV5* _seg = (seg); \
        if (__builtin_expect(!_seg, 0)) { \
            (SmallPageMetaV5*)NULL; \
        } else { \
            size_t _idx = SMALL_SEGMENT_V5_PAGE_IDX(_seg, (ptr)); \
            (__builtin_expect(_idx < _seg->num_pages, 1)) ? \
                &_seg->page_meta[_idx] : (SmallPageMetaV5*)NULL; \
        } \
    })

// SMALL_SEGMENT_V5_VALIDATE_MAGIC(seg) - magic 検証
#define SMALL_SEGMENT_V5_VALIDATE_MAGIC(seg) \
    (__builtin_expect((seg) && (seg)->magic == SMALL_SEGMENT_V5_MAGIC, 1))

// SMALL_SEGMENT_V5_VALIDATE_PTR(ptr) - Fail-Fast validation pipeline
// ptr が valid な v5 segment 内にあるかを検証
#define SMALL_SEGMENT_V5_VALIDATE_PTR(ptr) \
    ({  \
        int _valid = 0; \
        if (__builtin_expect((ptr) != NULL, 1)) { \
            SmallSegmentV5* _seg = SMALL_SEGMENT_V5_BASE_FROM_PTR(ptr); \
            if (SMALL_SEGMENT_V5_VALIDATE_MAGIC(_seg)) { \
                size_t _idx = SMALL_SEGMENT_V5_PAGE_IDX(_seg, (ptr)); \
                _valid = (_idx < _seg->num_pages); \
            } \
        } \
        _valid; \
    })

// SmallSegmentV5: セグメント構造体
typedef struct SmallSegmentV5 {
    uintptr_t        base;           // セグメント先頭アドレス
    uint32_t         num_pages;      // ページ数（通常は 32）
    uint32_t         owner_tid;      // オーナースレッド ID
    uint32_t         magic;          // 0xDEADBEEF for validation
    SmallPageMetaV5  page_meta[SMALL_SEGMENT_V5_NUM_PAGES];  // page metadata array
} SmallSegmentV5;

// API（v5-0 では宣言のみ、実装は v5-2）
SmallSegmentV5* small_segment_v5_acquire(void);
void            small_segment_v5_release(SmallSegmentV5* seg);
SmallPageMetaV5* small_segment_v5_page_meta_of(void* ptr);

// Page-level allocation (v5-2 fix for segment reuse)
SmallPageMetaV5* small_segment_v5_alloc_page(void);
void             small_segment_v5_free_page(SmallPageMetaV5* page);

#endif // HAKMEM_SMALLSEGMENT_V5_BOX_H