adjustToWorstCaseAlignment() simplify

Add some STATIC_ASSERT to check assumptions.

Only in-tree use is freeListLib to ensure chunks in
a malloc()'d block are aligned.

modules/libcom/src/misc/adjustment.c

@@ -15,40 +15,25 @@
 #include <stdlib.h>
 #include <stddef.h>
 
-/* Up to now epicsShareThings have been declared as imports
- *   (Appropriate for other stuff)
- * After setting the following they will be declared as exports
- *   (Appropriate for what we implement)
- */
+#include <epicsAssert.h>
 #include "adjustment.h"
 
-LIBCOM_API size_t adjustToWorstCaseAlignment(size_t size)
+size_t adjustToWorstCaseAlignment(size_t size)
 {
-    int align_size, adjust;
-    struct test_long_word { char c; long lw; };
-    struct test_double { char c; double d; };
-    struct test_ptr { char c; void *p; };
-    int test_long_size = sizeof(struct test_long_word) - sizeof(long);
-    int test_double_size = sizeof(struct test_double) - sizeof(double);
-    int test_ptr_size = sizeof(struct test_ptr) - sizeof(void *);
-    size_t adjusted_size = size;
+    union aline {
+        /* largest primative types (so far...) */
+        double dval;
+        size_t uval;
+        char *ptr;
+    };
 
-    /*
-     * Use Jeff's alignment tests to determine worst case of long,
-     * double or pointer alignment requirements.
-    */
-    align_size = test_long_size > test_ptr_size ?
-                  test_long_size : test_ptr_size;
+    /* assert that alignment size is a power of 2 */
+    STATIC_ASSERT((sizeof(union aline) & (sizeof(union aline)-1))==0);
 
-    align_size = align_size > test_double_size ?
-                  align_size : test_double_size;
+    /* round up to aligment size */
+    size--;
+    size |= sizeof(union aline)-1;
+    size++;
 
-    /*
-     * Increase the size to fit worst case alignment if not already
-     * properly aligned.
-     */
-    adjust = align_size - size%align_size;
-    if (adjust != align_size) adjusted_size += adjust;
-
-    return (adjusted_size);
+    return size;
 }