Does not work, probably a bug in block_split

yamalloc.c

@@ -0,0 +1,154 @@
+/*
+ * Yet Another Malloc
+ * yamalloc.c
+ */
+
+/* Feature test macros */
+
+#define _DEFAULT_SOURCE // for sbrk
+
+/* Includes */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdbool.h>
+
+#include "yamalloc.h"
+
+/* Constants */
+
+#define YA_SZ_WORD  (sizeof(intptr_t))
+#define YA_SZ_DWORD (2 * YA_SZ_WORD)
+#define YA_SZ_CHUNK 8192
+
+/* Macros */
+
+#define YA_IS_FREE(block) (((block)[0] & 1) == 0)
+#define YA_ROUND_DIV(n, m) (((n) + ((m)-1)) / (m))
+#define YA_ROUND(n, m) (YA_ROUND_DIV(n,m) * (m))
+
+/* Globals */
+
+intptr_t *heap_start = NULL;
+intptr_t *heap_end   = NULL;
+
+/* Local declarations */
+
+int heap_init();
+int heap_extend();
+
+void block_join(intptr_t *block);
+
+/* Function definitions */
+
+#ifdef YA_DEBUG
+void ya_print_blocks() {
+    for (intptr_t *ptr = heap_start; ptr < heap_end; ptr += ptr[0]) {
+        fprintf(stderr, "Block at %p, size %ld\n", ptr, ptr[0]);
+    }
+}
+#endif
+
+void block_join_prev(intptr_t *block) {
+    intptr_t *prev = block - block[-1];
+    if (prev >= heap_start && YA_IS_FREE(prev)) {
+        intptr_t size = prev[0] + block[0];
+        prev[0] = size;
+        block[block[0] - 1] = size;
+    }
+}
+
+void block_join_next(intptr_t *block) {
+    intptr_t *next = block + block[0];
+    if (next < heap_end && YA_IS_FREE(next)) {
+        intptr_t size = next[0] + block[0];
+        block[0] = size;
+        next[next[0] - 1] = size;
+    }
+}
+
+void block_join(intptr_t *block) {
+    if (block > heap_start) {
+        block_join_prev(block);
+    }
+    block_join_next(block);
+}
+
+void block_split(intptr_t *block, intptr_t size) {
+    intptr_t old_size = block[0];
+    block[0] = size;
+    block[size - 1] = size;
+    block[size] = old_size - size;
+    block[old_size - 1] = old_size - size;
+}
+
+int heap_init() {
+    heap_start = sbrk(0);    
+    if (heap_start == (void*) -1) {
+        heap_start = NULL;
+        heap_end = NULL;
+        return -1;
+    }
+    heap_end = heap_start;
+    return 0;
+}
+
+int heap_extend(intptr_t size_w) {
+    fprintf(stderr, "heap_extend: old heap_start = %p, heap_end = %p\n",
+            heap_start, heap_end);
+    intptr_t size = YA_ROUND(size_w * YA_SZ_WORD, YA_SZ_CHUNK);
+    size_w = size / YA_SZ_WORD;
+    fprintf(stderr, "heap_extend: %ld bytes, %ld words\n", size, size_w);
+    void *ptr = sbrk(size);
+    if (ptr == (void *) - 1) {
+        return -1;
+    }
+    fprintf(stderr, "heap_extend: %ld bytes, %ld words\n", size, size_w);
+    heap_end[0] = size_w;
+    heap_end[size_w - 1] = size_w;
+    fprintf(stderr, "heap_extend: heap_end = %p, heap_end + size_w = %p\n",
+            heap_end, heap_end + size_w);
+    fprintf(stderr, "heap_extend: heap_end[0] = %ld, heap_end[size_w - 1] = %ld\n",
+            heap_end[0], heap_end[size_w - 1]);
+    heap_end += size_w;
+    fprintf(stderr, "heap_extend: new heap_end = %p\n", heap_end);
+    block_join(ptr);
+    return 0;
+}
+
+void *malloc(size_t size) {
+    if (size == 0) {
+        return NULL;
+    }
+    if (heap_start == NULL || heap_end == NULL) {
+        if (heap_init() != 0) {
+            return NULL;
+        }
+    }
+    intptr_t size_w = YA_ROUND_DIV(size + 2, YA_SZ_WORD); // size in words
+    intptr_t align_dw = YA_ROUND(size_w, 2); // round to dword
+    intptr_t *block;
+    for (block = heap_start; block < heap_end; block += block[0]) {
+        if (YA_IS_FREE(block) && block[0] >= align_dw) {
+            break;
+        }
+    }
+    fprintf(stderr, "size_w = %ld, align_dw = %ld\n", size_w, align_dw);
+    if (block >= heap_end) { // could not find block, extend heap
+        if (heap_extend(align_dw) != 0) { 
+            return NULL;
+        }
+        block = heap_end - heap_end[-1];
+        if (!YA_IS_FREE(block) || block[0] < align_dw) {
+            return NULL;
+        }
+    }
+    if (block[0] > align_dw) {
+        block_split(block, align_dw);
+    }
+    block[0] |= 1;
+    return block + 1;
+}
+
+void free(void *ptr) {
+}

yamalloc.h

@@ -0,0 +1,19 @@
+/*
+ * Yet Another Malloc
+ * yamalloc.h
+ */
+
+#ifndef YAMALLOC_H
+#define YAMALLOC_H
+
+#include <stddef.h>
+
+#ifdef YA_DEBUG
+void ya_print_blocks();
+#endif
+
+void *malloc(size_t size);
+
+void free(void *ptr);
+
+#endif