Malloc source code

The two functions are taken from the unix version 6 malloc. in the c file, one is the malloc function and the other is the mfree function 2515:/* the map array is a list of idle resources, each storage area is defined by its length and relative address */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: {253 1: Register int A; 2532: Register struct map * bp; 2533: 2534: For (BP = mp; BP-> m_size; BP ++) {/* search for a map array, until the end of the map list is reached, or a free space meeting the request length */2535: If (BP-> m_size> = size) is found) {/* the idle block meets the request */2536: A = BP-> m_addr;/* record the first address of the zone */2537: BP-> m_addr = + size; /* the size of the first part of the idle block address is the size block allocated. Therefore, the size of the first part is forward */2538: If (BP-> m_size =-size) = 0) /* The allocated idle block size is exactly equal to the size of the requested space */2539: do {/* move the subsequent records of the space block in the map forward */2540: BP ++; 2541: (bp-1)-> m_addr = B P-> 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 previusly 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: * // * return a storage area with the size and starting address AA to map */2556: mfree (MP, size, AA) 2557: St Ruct 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 ++);/* search for map until you find the record where the starting address in map is less than the address of the released space */2565: If (BP> MP & (bp-1) -> m_addr + (bp-1)-> m_size = A) {/* release space and previous space consecutively */2566: (bp-1)-> m_size = + size; /* the size of the first element in the map increases the size of the space to be released */2567: if (a + size = BP-> m_addr) {/* Whether the released bucket is adjacent to the next block in map */2568: (bp-1)-> m_size = + bp-> m_size; /* merge the released block and the last block of storage */2569: While (BP-> m_size) {/* Forward the remaining block */2570: BP ++; 2571: (bp-1)-> m_addr = BP-> m_addr; 2572: (bp-1)-> m_size = BP-> m_size; 2573:} 2574:} 2575 :} else {/* not consecutive with the previous space */2576: if (a + size = BP-> m_addr & BP-> m_size) {/* Whether it is consecutive with the next space */2577: BP-> m_addr =-size; 2578: BP-> m_size = + size; 2579:} else if (size) do {/* release space is not 0, add a new record to map, and move the space record in the remainder of the map */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 :/*---------------------------*/