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/* Copyright (c) 2002, 2004, 2010 Joerg Wunsch
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Copyright (c) 2010 Gerben van den Broeke
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All rights reserved.
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malloc, free, realloc from avr-libc 1.7.0
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with minor modifications, by Paul Stoffregen
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in
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the documentation and/or other materials provided with the
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distribution.
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* Neither the name of the copyright holders nor the names of
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contributors may be used to endorse or promote products derived
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from this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <stdlib.h>
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#include <inttypes.h>
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#include <string.h>
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#include <avr/io.h>
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#define __MALLOC_MARGIN__ 120
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struct __freelist {
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size_t sz;
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struct __freelist *nx;
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};
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/*
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* Exported interface:
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*
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* When extending the data segment, the allocator will not try to go
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* beyond the current stack limit, decreased by __malloc_margin bytes.
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* Thus, all possible stack frames of interrupt routines that could
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* interrupt the current function, plus all further nested function
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* calls must not require more stack space, or they'll risk to collide
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* with the data segment.
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*/
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#define STACK_POINTER() ((char *)AVR_STACK_POINTER_REG)
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extern char __heap_start;
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char *__brkval = &__heap_start; // first location not yet allocated
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struct __freelist *__flp; // freelist pointer (head of freelist)
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char *__brkval_maximum = 100;
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void *
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malloc(size_t len)
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{
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struct __freelist *fp1, *fp2, *sfp1, *sfp2;
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char *cp;
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size_t s, avail;
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/*
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* Our minimum chunk size is the size of a pointer (plus the
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* size of the "sz" field, but we don't need to account for
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* this), otherwise we could not possibly fit a freelist entry
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* into the chunk later.
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*/
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if (len < sizeof(struct __freelist) - sizeof(size_t))
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len = sizeof(struct __freelist) - sizeof(size_t);
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/*
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* First, walk the free list and try finding a chunk that
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* would match exactly. If we found one, we are done. While
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* walking, note down the smallest chunk we found that would
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* still fit the request -- we need it for step 2.
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*
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*/
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for (s = 0, fp1 = __flp, fp2 = 0;
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fp1;
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fp2 = fp1, fp1 = fp1->nx) {
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if (fp1->sz < len)
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continue;
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if (fp1->sz == len) {
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/*
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* Found it. Disconnect the chunk from the
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* freelist, and return it.
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*/
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if (fp2)
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fp2->nx = fp1->nx;
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else
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__flp = fp1->nx;
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return &(fp1->nx);
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}
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else {
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if (s == 0 || fp1->sz < s) {
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/* this is the smallest chunk found so far */
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s = fp1->sz;
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sfp1 = fp1;
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sfp2 = fp2;
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}
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}
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}
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/*
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* Step 2: If we found a chunk on the freelist that would fit
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* (but was too large), look it up again and use it, since it
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* is our closest match now. Since the freelist entry needs
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* to be split into two entries then, watch out that the
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* difference between the requested size and the size of the
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* chunk found is large enough for another freelist entry; if
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* not, just enlarge the request size to what we have found,
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* and use the entire chunk.
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*/
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if (s) {
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if (s - len < sizeof(struct __freelist)) {
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/* Disconnect it from freelist and return it. */
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if (sfp2)
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sfp2->nx = sfp1->nx;
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else
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__flp = sfp1->nx;
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return &(sfp1->nx);
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}
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/*
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* Split them up. Note that we leave the first part
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* as the new (smaller) freelist entry, and return the
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* upper portion to the caller. This saves us the
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* work to fix up the freelist chain; we just need to
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* fixup the size of the current entry, and note down
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* the size of the new chunk before returning it to
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* the caller.
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*/
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cp = (char *)sfp1;
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s -= len;
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cp += s;
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sfp2 = (struct __freelist *)cp;
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sfp2->sz = len;
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sfp1->sz = s - sizeof(size_t);
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return &(sfp2->nx);
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}
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/*
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* Step 3: If the request could not be satisfied from a
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* freelist entry, just prepare a new chunk. This means we
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* need to obtain more memory first. The largest address just
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* not allocated so far is remembered in the brkval variable.
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* Under Unix, the "break value" was the end of the data
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* segment as dynamically requested from the operating system.
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* Since we don't have an operating system, just make sure
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* that we don't collide with the stack.
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*/
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cp = STACK_POINTER() - __MALLOC_MARGIN__;
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if (cp <= __brkval)
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/*
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* Memory exhausted.
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*/
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return 0;
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avail = cp - __brkval;
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/*
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* Both tests below are needed to catch the case len >= 0xfffe.
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*/
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if (avail >= len && avail >= len + sizeof(size_t)) {
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fp1 = (struct __freelist *)__brkval;
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__brkval += len + sizeof(size_t);
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__brkval_maximum = __brkval;
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fp1->sz = len;
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return &(fp1->nx);
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}
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/*
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* Step 4: There's no help, just fail. :-/
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*/
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return 0;
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}
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void
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free(void *p)
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{
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struct __freelist *fp1, *fp2, *fpnew;
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char *cp1, *cp2, *cpnew;
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/* ISO C says free(NULL) must be a no-op */
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if (p == 0)
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return;
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cpnew = p;
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cpnew -= sizeof(size_t);
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fpnew = (struct __freelist *)cpnew;
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fpnew->nx = 0;
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/*
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* Trivial case first: if there's no freelist yet, our entry
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* will be the only one on it. If this is the last entry, we
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* can reduce __brkval instead.
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*/
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if (__flp == 0) {
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if ((char *)p + fpnew->sz == __brkval)
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__brkval = cpnew;
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else
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__flp = fpnew;
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return;
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}
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/*
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* Now, find the position where our new entry belongs onto the
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* freelist. Try to aggregate the chunk with adjacent chunks
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* if possible.
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*/
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for (fp1 = __flp, fp2 = 0;
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fp1;
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fp2 = fp1, fp1 = fp1->nx) {
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if (fp1 < fpnew)
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continue;
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cp1 = (char *)fp1;
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fpnew->nx = fp1;
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if ((char *)&(fpnew->nx) + fpnew->sz == cp1) {
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/* upper chunk adjacent, assimilate it */
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fpnew->sz += fp1->sz + sizeof(size_t);
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fpnew->nx = fp1->nx;
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}
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if (fp2 == 0) {
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/* new head of freelist */
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__flp = fpnew;
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return;
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}
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break;
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}
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/*
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* Note that we get here either if we hit the "break" above,
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* or if we fell off the end of the loop. The latter means
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* we've got a new topmost chunk. Either way, try aggregating
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* with the lower chunk if possible.
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*/
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fp2->nx = fpnew;
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cp2 = (char *)&(fp2->nx);
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if (cp2 + fp2->sz == cpnew) {
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/* lower junk adjacent, merge */
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fp2->sz += fpnew->sz + sizeof(size_t);
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fp2->nx = fpnew->nx;
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}
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/*
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* If there's a new topmost chunk, lower __brkval instead.
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*/
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for (fp1 = __flp, fp2 = 0;
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fp1->nx != 0;
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fp2 = fp1, fp1 = fp1->nx)
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/* advance to entry just before end of list */;
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cp2 = (char *)&(fp1->nx);
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if (cp2 + fp1->sz == __brkval) {
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if (fp2 == NULL)
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/* Freelist is empty now. */
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__flp = NULL;
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else
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fp2->nx = NULL;
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__brkval = cp2 - sizeof(size_t);
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}
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}
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void *
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realloc(void *ptr, size_t len)
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{
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struct __freelist *fp1, *fp2, *fp3, *ofp3;
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char *cp, *cp1;
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void *memp;
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size_t s, incr;
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/* Trivial case, required by C standard. */
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if (ptr == 0)
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return malloc(len);
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cp1 = (char *)ptr;
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cp1 -= sizeof(size_t);
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fp1 = (struct __freelist *)cp1;
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cp = (char *)ptr + len; /* new next pointer */
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if (cp < cp1)
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/* Pointer wrapped across top of RAM, fail. */
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return 0;
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/*
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* See whether we are growing or shrinking. When shrinking,
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* we split off a chunk for the released portion, and call
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* free() on it. Therefore, we can only shrink if the new
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* size is at least sizeof(struct __freelist) smaller than the
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* previous size.
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*/
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if (len <= fp1->sz) {
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/* The first test catches a possible unsigned int
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* rollover condition. */
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if (fp1->sz <= sizeof(struct __freelist) ||
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len > fp1->sz - sizeof(struct __freelist))
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return ptr;
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fp2 = (struct __freelist *)cp;
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fp2->sz = fp1->sz - len - sizeof(size_t);
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fp1->sz = len;
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free(&(fp2->nx));
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return ptr;
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}
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/*
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* If we get here, we are growing. First, see whether there
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* is space in the free list on top of our current chunk.
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*/
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incr = len - fp1->sz;
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cp = (char *)ptr + fp1->sz;
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fp2 = (struct __freelist *)cp;
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for (s = 0, ofp3 = 0, fp3 = __flp;
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fp3;
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ofp3 = fp3, fp3 = fp3->nx) {
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if (fp3 == fp2 && fp3->sz + sizeof(size_t) >= incr) {
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/* found something that fits */
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if (fp3->sz + sizeof(size_t) - incr > sizeof(struct __freelist)) {
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/* split off a new freelist entry */
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cp = (char *)ptr + len;
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fp2 = (struct __freelist *)cp;
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fp2->nx = fp3->nx;
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fp2->sz = fp3->sz - incr;
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fp1->sz = len;
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} else {
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/* it just fits, so use it entirely */
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fp1->sz += fp3->sz + sizeof(size_t);
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fp2 = fp3->nx;
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}
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if (ofp3)
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ofp3->nx = fp2;
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else
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__flp = fp2;
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return ptr;
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}
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/*
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* Find the largest chunk on the freelist while
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* walking it.
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*/
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if (fp3->sz > s)
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s = fp3->sz;
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}
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/*
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* If we are the topmost chunk in memory, and there was no
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* large enough chunk on the freelist that could be re-used
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* (by a call to malloc() below), quickly extend the
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* allocation area if possible, without need to copy the old
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* data.
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*/
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if (__brkval == (char *)ptr + fp1->sz && len > s) {
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cp = (char *)ptr + len;
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cp1 = STACK_POINTER() - __MALLOC_MARGIN__;
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if (cp < cp1) {
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__brkval = cp;
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__brkval_maximum = cp;
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fp1->sz = len;
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return ptr;
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}
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/* If that failed, we are out of luck. */
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return 0;
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}
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/*
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* Call malloc() for a new chunk, then copy over the data, and
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* release the old region.
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*/
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if ((memp = malloc(len)) == 0)
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return 0;
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memcpy(memp, ptr, fp1->sz);
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free(ptr);
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return memp;
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}
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