realloc.c - scc - simple c99 compiler
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       ---
       realloc.c (1330B)
       ---
            1 #include <errno.h>
            2 #include <stdint.h>
            3 #include <stdlib.h>
            4 #include <string.h>
            5 
            6 #include "malloc.h"
            7 #undef realloc
            8 
            9 void *
           10 realloc(void *ptr, size_t nbytes)
           11 {
           12         Header *oh, *prev, *next, *new;
           13         size_t nunits, avail, onbytes, n;
           14 
           15         if (nbytes == 0) {
           16                 free(ptr);
           17                 ptr = NULL;
           18         } else if (nbytes > SIZE_MAX - sizeof(Header)-1) {
           19                 errno = ENOMEM;
           20                 return NULL;
           21         }
           22 
           23         if (!ptr)
           24                 return malloc(nbytes);
           25 
           26         nunits = (nbytes+sizeof(Header)-1)/sizeof(Header) + 1;
           27         oh = (Header *) ptr - 1;
           28 
           29         if (oh->h.size == nunits)
           30                 return ptr;
           31 
           32         new = oh + nunits;
           33 
           34         if (nunits < oh->h.size) {
           35                 new->h.size = oh->h.size - nunits;
           36                 oh->h.size = nunits;
           37                 free(new + 1);
           38                 return ptr;
           39         }
           40 
           41         prev = _prevchunk(oh);
           42         next = prev->h.next;
           43 
           44         if (oh + oh->h.size == next) {
           45                 /*
           46                  * if there is free space adjacent
           47                  * to the current memory
           48                  */
           49                 avail = oh->h.size + next->h.size;
           50 
           51                 if (avail == nunits) {
           52                         oh->h.size = nunits;
           53                         prev->h.next = next->h.next;
           54                         _freep = prev;
           55                         return ptr;
           56                 }
           57 
           58                 if (nunits < avail) {
           59                         oh->h.size = nunits;
           60                         prev->h.next = new;
           61                         new->h.next = next->h.next;
           62                         new->h.size = avail - nunits;
           63                         _freep = new;
           64                         return ptr;
           65                 }
           66         }
           67 
           68         if ((new = malloc(nbytes)) == NULL)
           69                 return NULL;
           70 
           71         n = (oh->h.size - 1) * sizeof(Header);
           72         if (n > nbytes)
           73                 n = nbytes;
           74         memcpy(new, ptr, n);
           75         free(ptr);
           76 
           77         return new;
           78 }