/* * libc/stdlib/malloc/heap_free.c -- return memory to a heap * * Copyright (C) 2002 NEC Corporation * Copyright (C) 2002 Miles Bader <miles@gnu.org> * * This file is subject to the terms and conditions of the GNU Lesser * General Public License. See the file COPYING.LIB in the main * directory of this archive for more details. * * Written by Miles Bader <miles@gnu.org> */ #include <stdlib.h> #include "heap.h" /* Return the memory area MEM of size SIZE to HEAP. */ struct heap_free_area * __heap_free (struct heap *heap, void *mem, size_t size) { struct heap_free_area *prev_fa, *fa; void *end = (char *)mem + size; HEAP_DEBUG (heap, "before __heap_free"); /* Find an adjacent free-list entry. */ for (prev_fa = 0, fa = heap->free_areas; fa; prev_fa = fa, fa = fa->next) { size_t fa_size = fa->size; void *fa_mem = HEAP_FREE_AREA_START (fa); if (fa_mem > end) /* We've reached the right spot in the free-list without finding an adjacent free-area, so continue below to add a new free area. */ break; else if (fa_mem == end) /* FA is just after MEM, grow down to encompass it. */ { fa_size += size; /* See if FA can now be merged with its predecessor. */ if (prev_fa && mem == HEAP_FREE_AREA_END (prev_fa)) /* Yup; merge PREV_FA's info into FA. */ { fa_size += prev_fa->size; __heap_link_free_area_after (heap, fa, prev_fa->prev); } fa->size = fa_size; goto done; } else if (HEAP_FREE_AREA_END (fa) == mem) /* FA is just before MEM, expand to encompass it. */ { struct heap_free_area *next_fa = fa->next; fa_size += size; /* See if FA can now be merged with its successor. */ if (next_fa && end == HEAP_FREE_AREA_START (next_fa)) /* Yup; merge FA's info into NEXT_FA. */ { fa_size += next_fa->size; __heap_link_free_area_after (heap, next_fa, prev_fa); fa = next_fa; } else /* FA can't be merged; move the descriptor for it to the tail-end of the memory block. */ { /* The new descriptor is at the end of the extended block, SIZE bytes later than the old descriptor. */ fa = (struct heap_free_area *)((char *)fa + size); /* Update links with the neighbors in the list. */ __heap_link_free_area (heap, fa, prev_fa, next_fa); } fa->size = fa_size; goto done; } } /* Make MEM into a new free-list entry. */ fa = __heap_add_free_area (heap, mem, size, prev_fa, fa); done: HEAP_DEBUG (heap, "after __heap_free"); return fa; }