alloc-util: cleanups

This patch contains a set of little cleanups for alloc-util.h:

1. The malloc_multiply(), realloc_multiply() and memdup_multiply()
functions check allocation related parameters on overflow. Let's
move them to the separate size_multiply_overflow() function for
simplicity, code duplication prevention and possible reuse in future.

2. use SIZE_MAX from stdlib instead of ((size_t) - 1) to be more
clear.

3. The 'a'/'b' variables are renamed to 'size' and 'need' to be
more clear.'

1 files changed, 13 insertions, 9 deletions

diff --git a/src/basic/alloc-util.h b/src/basic/alloc-util.h
index 679ba7f398..ceeee519b7 100644
--- a/src/basic/alloc-util.h
+++ b/src/basic/alloc-util.h
@@ -51,25 +51,29 @@ static inline void freep(void *p) {
 
 #define _cleanup_free_ _cleanup_(freep)
 
-_malloc_  _alloc_(1, 2) static inline void *malloc_multiply(size_t a, size_t b) {
-        if (_unlikely_(b != 0 && a > ((size_t) -1) / b))
+static inline bool size_multiply_overflow(size_t size, size_t need) {
+        return _unlikely_(need != 0 && size > (SIZE_MAX / need));
+}
+
+_malloc_  _alloc_(1, 2) static inline void *malloc_multiply(size_t size, size_t need) {
+        if (size_multiply_overflow(size, need))
                 return NULL;
 
-        return malloc(a * b);
+        return malloc(size * need);
 }
 
-_alloc_(2, 3) static inline void *realloc_multiply(void *p, size_t a, size_t b) {
-        if (_unlikely_(b != 0 && a > ((size_t) -1) / b))
+_alloc_(2, 3) static inline void *realloc_multiply(void *p, size_t size, size_t need) {
+        if (size_multiply_overflow(size, need))
                 return NULL;
 
-        return realloc(p, a * b);
+        return realloc(p, size * need);
 }
 
-_alloc_(2, 3) static inline void *memdup_multiply(const void *p, size_t a, size_t b) {
-        if (_unlikely_(b != 0 && a > ((size_t) -1) / b))
+_alloc_(2, 3) static inline void *memdup_multiply(const void *p, size_t size, size_t need) {
+        if (size_multiply_overflow(size, need))
                 return NULL;
 
-        return memdup(p, a * b);
+        return memdup(p, size * need);
 }
 
 void* greedy_realloc(void **p, size_t *allocated, size_t need, size_t size);