malloc 源码

阳光穿透心脏的1/2处 2024-02-19 13:16 8阅读 0赞

1.  两个函数取自UNIX 版本6 malloc.c文件，一个为malloc函数，一个为mfree函数 
2.  2515:/\*map数组是一个空闲资源列表，其中每个存储区由其长度和相对地址定义\*/
3.  **struct** map 
4.  2516: \{ 
5.  2517: **char** \*m\_size; 
6.  2518: **char** \*m\_addr; 
7.  2519: \}; 
8.  2520: /\* --------------------------- \*/
9.  2521: 
10. 2522: /\*
11. 2523: \* Allocate size units from the given
12. 2524: \* map. Return the base of the allocated
13. 2525: \* space.
14. 2526: \* Algorithm is first fit.
15. 2527: \*/
16. 2528: malloc(mp, size) 
17. 2529: **struct** map \*mp; 
18. 2530: \{ 
19. 2531: **register****int** a; 
20. 2532: **register****struct** map \*bp; 
21. 2533: 
22. 2534: **for** (bp = mp; bp->m\_size; bp++) \{ /\*搜索map数组，直到到达map列表尾部，或者搜索到一个长度满足请求的空闲空间\*/
23. 2535: **if** (bp->m\_size >= size) \{ /\*该空闲块满足请求\*/
24. 2536: a = bp->m\_addr; /\*记录该区首地址\*/
25. 2537: bp->m\_addr =+ size; /\*空闲块地址首端大小为size块被分配，因此首地址前移size\*/
26. 2538: **if** ((bp->m\_size =- size) == 0) /\*分配的空闲块大小刚好等于请求空间的大小\*/
27. 2539: **do** \{ /\*将该空间块在map中的后继记录前移\*/
28. 2540: bp++; 
29. 2541: (bp-1)->m\_addr = bp->m\_addr; 
30. 2542: \} **while** ((bp-1)->m\_size = bp->m\_size); 
31. 2543: **return**(a); 
32. 2544: \} 
33. 2545: \} 
34. 2546: **return**(0); 
35. 2547: \} 
36. 2548: /\* --------------------------- \*/
37. 2549: 
38. 2550: /\*
39. 2551: \* Free the previously allocated space aa
40. 2552: \* of size units into the specified map.
41. 2553: \* Sort aa into map and combine on
42. 2554: \* one or both ends if possible.
43. 2555: \*/
44. /\*将一个大小为size，起始地址为aa的存储区还给map\*/
45. 2556: mfree(mp, size, aa) 
46. 2557: **struct** map \*mp; 
47. 2558: \{ 
48. 2559: **register****struct** map \*bp; 
49. 2560: **register****int** t; 
50. 2561: **register****int** a; 
51. 2562: 
52. 2563: a = aa; 
53. 2564: **for** (bp = mp; bp->m\_addr<=a && bp->m\_size!=0; bp++); /\*搜索map，直到找到map中起始地址小于释放空间地址的记录\*/
54. 2565: **if** (bp>mp && (bp-1)->m\_addr+(bp-1)->m\_size == a) \{ /\*释放空间和前一空间连续\*/
55. 2566: (bp-1)->m\_size =+ size; /\*map中前一元素的大小增加被释放空间的大小\*/
56. 2567: **if** (a+size == bp->m\_addr) \{ /\*释放的存储区是否与map中下一个区块相邻\*/
57. 2568: (bp-1)->m\_size =+ bp->m\_size; /\*合并被释放块和后一块存储区\*/
58. 2569: **while** (bp->m\_size) \{ /\*前移余下的存储区\*/
59. 2570: bp++; 
60. 2571: (bp-1)->m\_addr = bp->m\_addr; 
61. 2572: (bp-1)->m\_size = bp->m\_size; 
62. 2573: \} 
63. 2574: \} 
64. 2575: \} **else** \{ /\*不与前一空间连续\*/
65. 2576: **if** (a+size == bp->m\_addr && bp->m\_size) \{ /\*是否与后一空间连续\*/
66. 2577: bp->m\_addr =- size; 
67. 2578: bp->m\_size =+ size; 
68. 2579: \} **else****if** (size) **do** \{ /\*释放空间大小不为0，在map中加入新记录，后移map中余下的空间记录\*/
69. 2580: t = bp->m\_addr; 
70. 2581: bp->m\_addr = a; 
71. 2582: a = t; 
72. 2583: t = bp->m\_size; 
73. 2584: bp->m\_size = size; 
74. 2585: bp++; 
75. 2586: \} **while** (size = t); 
76. 2587: \} 
77. 2588: \} 
78. 2589: /\* --------------------------- \*/
79.