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/**
* @file heap.c
* A basic memory manager
*
* Copyright (C) 2018 Clyne Sullivan
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include "heap.h"
// Defines size of alignment on memory allocations
#define HEAP_ALIGN 4
// Linked list of free'd memory
static alloc_t *free_blocks;
static void *heap_end;
void heap_init(void *buf)
{
heap_end = buf;
free_blocks = 0;
}
uint32_t heap_free(void)
{
uint32_t total = 0;
// Count free'd block sizes
for (alloc_t *node = free_blocks; node != 0; node = node->next)
total += node->size;
// Add remaining free memory to that total
return total + (0x20018000 - (uint32_t)heap_end);
}
void *malloc(uint32_t size)
{
if (size == 0)
return 0;
// Round size to an aligned value
size = (size + sizeof(alloc_t) + HEAP_ALIGN) & ~(HEAP_ALIGN - 1);
// Begin searching through free'd blocks to see if we can reuse some memory.
alloc_t *node = free_blocks;
alloc_t *prev = 0;
while (node != 0) {
if (node->size >= size) {
// If we can use this chunk, remove it from the free_blocks chain
if (prev != 0)
prev->next = node->next;
else
free_blocks = node->next;
node->next = 0;
// If this chunk is really big, give back the extra space
if (node->size > size + 64) { // TODO why 64..?
alloc_t *leftover = (alloc_t *)((uint32_t)node
+ sizeof(alloc_t) + size);
leftover->size = node->size - size - sizeof(alloc_t);
leftover->next = 0;
free((uint8_t *)leftover + sizeof(alloc_t));
node->size = size;
return (void *)((uint8_t *)node + sizeof(alloc_t));
}
return (void *)((uint8_t *)node + sizeof(alloc_t));
}
prev = node;
node = node->next;
}
// No reusable chunks, take from the end of the heap
node = (alloc_t *)heap_end;
node->size = size;
node->next = 0;
heap_end = (void *)((uint8_t *)heap_end + size);
return (void *)((uint8_t *)node + sizeof(alloc_t));
}
void *calloc(uint32_t count, uint32_t size)
{
// Simply malloc and zero
uint8_t *buf = malloc(count * size);
for (uint32_t i = 0; i < count * size; i++)
buf[i] = 0; // TODO safe?
return buf;
}
void free(void *buf)
{
if (buf == 0)
return;
// Get the alloc_t structure of this chunk
alloc_t *alloc = (alloc_t *)((uint8_t *)buf - sizeof(alloc_t));
if (alloc->next != 0)
return;
// Search through the free_blocks list to see if this free chunk can merge
// into an adjacent free chunk.
int merged = 0;
for (alloc_t *prev = 0, *node = free_blocks; node != 0; prev = node, node = node->next) {
// If the node after the current one is ours
if ((uint32_t)node + sizeof(alloc_t) + node->size == (uint32_t)alloc) {
// Merge by adding our node's size to this one
merged |= 1;
node->size += sizeof(alloc_t) + alloc->size;
break;
}
// Or, if this current node is the one after ours
else if ((uint32_t)buf + alloc->size == (uint32_t)node) {
// Merge the current node into ours
merged |= 1;
alloc->size += sizeof(alloc_t) + node->size;
alloc->next = node->next;
// Take the current node's place in the free_blocks chain
if (prev != 0)
prev->next = alloc;
else
free_blocks = alloc;
break;
}
}
// If we couldn't merge, simply append to the chain
if (merged == 0) {
alloc->next = free_blocks;
free_blocks = alloc;
}
}
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