malloc 源码

 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*/      struct map 2516: {2517:         char *m_size;2518:         char *m_addr;2519: };2520: /* ---------------------------       */2521: 2522: /*2523:  * Allocate size units from the given2524:  * map. Return the base of the allocated2525:  * space.2526:  * Algorithm is first fit.2527:  */2528: malloc(mp, size)2529: struct map *mp;2530: {2531:         register int a;2532:         register struct map *bp;2533: 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*/2535:                 if (bp->m_size >= size) { /*该空闲块满足请求*/2536:                         a = bp->m_addr;   /*记录该区首地址*/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*/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*/2539:                                 do {    /*将该空间块在map中的后继记录前移*/2540:                                         bp++;2541:                                         (bp-1)->m_addr = bp->m_addr;2542:                                 } while ((bp-1)->m_size = bp->m_size);2543:                         return(a);2544:                 }2545:         }2546:         return(0);2547: }2548: /* ---------------------------       */2549: 2550: /*2551:  * Free the previously allocated space aa2552:  * of size units into the specified map.2553:  * Sort aa into map and combine on2554:  * one or both ends if possible.2555:  */  /*将一个大小为size，起始地址为aa的存储区还给map*/2556: mfree(mp, size, aa)2557: struct map *mp;2558: {2559:         register struct map *bp;2560:         register int t;2561:         register int a;2562: 2563:         a = aa;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*/2565:         if (bp>mp && (bp-1)->m_addr+(bp-1)->m_size == a) { /*释放空间和前一空间连续*/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*/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*/2568:                         (bp-1)->m_size =+ bp->m_size; /*合并被释放块和后一块存储区*/2569:                         while (bp->m_size) { /*前移余下的存储区*/2570:                                 bp++;2571:                                 (bp-1)->m_addr = bp->m_addr;2572:                                 (bp-1)->m_size = bp->m_size;2573:                         }2574:                 }2575:         } else { /*不与前一空间连续*/2576:                 if (a+size == bp->m_addr && bp->m_size) { /*是否与后一空间连续*/2577:                         bp->m_addr =- size;2578:                         bp->m_size =+ size;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*/2580:                         t = bp->m_addr;2581:                         bp->m_addr = a;2582:                         a = t;2583:                         t = bp->m_size;2584:                         bp->m_size = size;2585:                         bp++;2586:                 } while (size = t);2587:         }2588: }2589: /* ---------------------------       */