/**
 * @file tiny_layout_box.h
 * @brief Box: Tiny Allocator Layout Definitions
 *
 * MISSION: Single source of truth for class size and header layout
 *
 * Current Design (Phase E1-CORRECT):
 * - All classes (0-7) have 1-byte header
 * - User pointer = base + 1 for classes 0-6, base + 0 for class 7
 *   (Note: Class 7 is headerless in practice but marked for consistency)
 * - No external code should hardcode offsets
 */

#ifndef TINY_LAYOUT_BOX_H
#define TINY_LAYOUT_BOX_H

#include <stddef.h>
#include "../hakmem_tiny_config.h" // For g_tiny_class_sizes and TINY_NUM_CLASSES

// Define all class-specific layout parameters
// Current: Defined in g_tiny_class_sizes[8] in hakmem_tiny.c
// This file makes them accessible via a unified Box API

// Header size is 1 byte when enabled
#define TINY_HEADER_SIZE 1

// Validation macros
static inline int tiny_class_is_valid(int class_idx) {
    return class_idx >= 0 && class_idx < TINY_NUM_CLASSES;
}

static inline size_t tiny_class_stride(int class_idx) {
    // Use the extern global definition from hakmem_tiny_config.h
    // g_tiny_class_sizes is defined in core/hakmem_tiny_config_box.inc
    return tiny_class_is_valid(class_idx) ? g_tiny_class_sizes[class_idx] : 0;
}

// Calculate user pointer offset from base pointer
// This logic centralizes the "User = Base + 1" vs "User = Base + 0" decision
static inline size_t tiny_user_offset(int class_idx) {
#if HAKMEM_TINY_HEADER_CLASSIDX
    // C0 (8B): offset 0 (8B stride too small for header + 8B pointer - would overflow)
    // C7 (2048B): offset 0 (overwrites header in freelist - largest class can tolerate)
    // C1-C6: offset 1 (header preserved - user data is not disturbed)
    // Optimized: Use bitmask lookup instead of branching
    // Bit pattern: C0=0, C1-C6=1, C7=0 → 0b01111110 = 0x7E
    return (0x7Eu >> class_idx) & 1u;
#else
    (void)class_idx;
    return 0u;
#endif
}

#endif // TINY_LAYOUT_BOX_H