兩個函數取自UNIX 版本6 malloc.c文件，一個為malloc函數，一個為mfree函數
2515:/map數組是一個空閑資源列表，其中每個存儲區由其長度和相對地址定義/
struct map
2516: {
2517: char *m_size;
2518: char *m_addr;
2519: };
2520: /* ————————— */
2521:
2522: /*
2523: * Allocate size units from the given
2524: * map. Return the base of the allocated
2525: * 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數組，直到到達map列表尾部，或者搜索到一個長度滿足請求的空閑空間/
2535: if (bp->m_size >= size) { /該空閑塊滿足請求/
2536: a = bp->m_addr; /記錄該區首地址/
2537: bp->m_addr =+ size; /空閑塊地址首端大小為size塊被分配，因此首地址前移size/
2538: if ((bp->m_size =- size) == 0) /分配的空閑塊大小剛好等于請求空間的大小/
2539: do { /將該空間塊在map中的后繼記錄前移/
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 aa
2552: * of size units into the specified map.
2553: * Sort aa into map and combine on
2554: * one or both ends if possible.
2555: */
/將一個大小為size，起始地址為aa的存儲區還給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中起始地址小于釋放空間地址的記錄/
2565: if (bp>mp && (bp-1)->m_addr+(bp-1)->m_size == a) { /釋放空間和前一空間連續/
2566: (bp-1)->m_size =+ size; /map中前一元素的大小增加被釋放空間的大小/
2567: if (a+size == bp->m_addr) { /釋放的存儲區是否與map中下一個區塊相鄰/
2568: (bp-1)->m_size =+ bp->m_size; /合并被釋放塊和后一塊存儲區/
2569: while (bp->m_size) { /前移余下的存儲區/
2570: bp++;
2571: (bp-1)->m_addr = bp->m_addr;
2572: (bp-1)->m_size = bp->m_size;
2573: }
2574: }
2575: } else { /不與前一空間連續/
2576: if (a+size == bp->m_addr && bp->m_size) { /是否與后一空間連續/
2577: bp->m_addr =- size;
2578: bp->m_size =+ size;
2579: } else if (size) do { /釋放空間大小不為0，在map中加入新記錄，后移map中余下的空間記錄/
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: /* ————————— */

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