55 lines
1.9 KiB
C
55 lines
1.9 KiB
C
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/**
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* @file tiny_layout_box.h
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* @brief Box: Tiny Allocator Layout Definitions
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*
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* MISSION: Single source of truth for class size and header layout
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*
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* Current Design (Phase E1-CORRECT):
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* - All classes (0-7) have 1-byte header
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* - User pointer = base + 1 for classes 0-6, base + 0 for class 7
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* (Note: Class 7 is headerless in practice but marked for consistency)
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* - No external code should hardcode offsets
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*/
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#ifndef TINY_LAYOUT_BOX_H
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#define TINY_LAYOUT_BOX_H
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#include <stddef.h>
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#include "../hakmem_tiny_config.h" // For g_tiny_class_sizes and TINY_NUM_CLASSES
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// Define all class-specific layout parameters
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// Current: Defined in g_tiny_class_sizes[8] in hakmem_tiny.c
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// This file makes them accessible via a unified Box API
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// Header size is 1 byte when enabled
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#define TINY_HEADER_SIZE 1
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// Validation macros
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static inline int tiny_class_is_valid(int class_idx) {
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return class_idx >= 0 && class_idx < TINY_NUM_CLASSES;
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}
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static inline size_t tiny_class_stride(int class_idx) {
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// Use the extern global definition from hakmem_tiny_config.h
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// g_tiny_class_sizes is defined in core/hakmem_tiny_config_box.inc
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return tiny_class_is_valid(class_idx) ? g_tiny_class_sizes[class_idx] : 0;
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}
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// Calculate user pointer offset from base pointer
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// This logic centralizes the "User = Base + 1" vs "User = Base + 0" decision
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static inline size_t tiny_user_offset(int class_idx) {
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#if HAKMEM_TINY_HEADER_CLASSIDX
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// C0 (8B): offset 0 (8B stride too small for header + 8B pointer - would overflow)
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// C7 (2048B): offset 0 (overwrites header in freelist - largest class can tolerate)
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// C1-C6: offset 1 (header preserved - user data is not disturbed)
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// Optimized: Use bitmask lookup instead of branching
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// Bit pattern: C0=0, C1-C6=1, C7=0 → 0b01111110 = 0x7E
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return (0x7Eu >> class_idx) & 1u;
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#else
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(void)class_idx;
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return 0u;
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#endif
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}
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#endif // TINY_LAYOUT_BOX_H
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