Correctness fixes and (optional) better C stdlib integration

- Add early NULL check to ta_free()
- Add overflow checks in alloc_block() and ta_calloc()
- Clear full block size to 0's in ta_calloc()
- Optionally set errno to ENOMEM when out of memory
- Optionally use memset() to implement memclear()
- Add ta_getsize() to return allocated block size
- Add ta_realloc() (optional, requires memcpy())

ta_getsize() and ta_realloc() are based on ideas from thi-ng#11, but rewritten
to fix various issues in that PR.

tinyalloc.c

@@ -9,6 +9,12 @@ extern void print_i(size_t);
 #define print_i(X)
 #endif
 
+/* optional C stdlib integration */
+#ifdef TA_USE_STDLIB
+#include <errno.h>
+#include <string.h>
+#endif
+
 typedef struct Block Block;
 
 struct Block {
@@ -134,6 +140,9 @@ bool ta_init(const void *base, const void *limit, const size_t heap_blocks, cons
 }
 
 bool ta_free(void *free) {
+    if (free == NULL) {
+        return false;
+    }
     Block *block = heap->used;
     Block *prev  = NULL;
     while (block != NULL) {
@@ -159,7 +168,11 @@ static Block *alloc_block(size_t num) {
     Block *ptr  = heap->free;
     Block *prev = NULL;
     size_t top  = heap->top;
+    size_t orig = num;
     num         = (num + heap_alignment - 1) & -heap_alignment;
+    if (num < orig) {
+        return NULL;  // overflow
+    }
     while (ptr != NULL) {
         const int is_top = ((size_t)ptr->addr + ptr->size >= top) && ((size_t)ptr->addr + num <= (size_t)heap_limit);
         if (is_top || ptr->size >= num) {
@@ -218,9 +231,15 @@ void *ta_alloc(size_t num) {
     if (block != NULL) {
         return block->addr;
     }
+#ifdef TA_USE_STDLIB
+    errno = ENOMEM;
+#endif
     return NULL;
 }
 
+#ifdef TA_USE_STDLIB
+#define memclear(ptr, num) memset((ptr), 0, (num))
+#else
 static void memclear(void *ptr, size_t num) {
     size_t *ptrw = (size_t *)ptr;
     size_t numw  = (num & -sizeof(size_t)) / sizeof(size_t);
@@ -233,14 +252,23 @@ static void memclear(void *ptr, size_t num) {
         *ptrb++ = 0;
     }
 }
+#endif
 
 void *ta_calloc(size_t num, size_t size) {
+    size_t orig = num;
     num *= size;
+    if (size != 0 && num / size != orig) {
+        goto overflow;
+    }
     Block *block = alloc_block(num);
     if (block != NULL) {
-        memclear(block->addr, num);
+        memclear(block->addr, block->size);
         return block->addr;
     }
+overflow:
+#ifdef TA_USE_STDLIB
+    errno = ENOMEM;
+#endif
     return NULL;
 }
 
@@ -268,3 +296,41 @@ size_t ta_num_fresh() {
 bool ta_check() {
     return heap_max_blocks == ta_num_free() + ta_num_used() + ta_num_fresh();
 }
+
+size_t ta_getsize(void *ptr) {
+    if (ptr == NULL) {
+        return 0;
+    }
+    Block *block = heap->used;
+    while (block != NULL) {
+        if (ptr == block->addr) {
+            return block->size;
+        }
+        block = block->next;
+    }
+    return 0;
+}
+
+/* requires memcpy() */
+#ifdef TA_USE_STDLIB
+void *ta_realloc(void *ptr, size_t num) {
+    if (ptr == NULL) {
+        return ta_alloc(num);
+    } else if (num == 0) {
+        ta_free(ptr);
+        return NULL;
+    }
+    size_t size  = ta_getsize(ptr);
+    Block *block = alloc_block(num);
+    if (block != NULL) {
+        if (size > num) {
+            size = num;
+        }
+        memcpy(block->addr, ptr, size);
+        ta_free(ptr);
+        return block->addr;
+    }
+    errno = ENOMEM;
+    return NULL;
+}
+#endif

tinyalloc.h

@@ -9,6 +9,12 @@ bool ta_init(const void *base, const void *limit, const size_t heap_blocks, cons
 void *ta_alloc(size_t num);
 void *ta_calloc(size_t num, size_t size);
 bool ta_free(void *ptr);
+size_t ta_getsize(void *ptr);
+
+/* requires memcpy() */
+#ifdef TA_USE_STDLIB
+void *ta_realloc(void *ptr, size_t num);
+#endif
 
 size_t ta_num_free();
 size_t ta_num_used();