add offset test

test/offset.c

@@ -0,0 +1,38 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static const unsigned size_classes[] = {
+    /* large */ 4 * 1024 * 1024,
+    /* 0 */ 0,
+    /* 16 */ 16, 32, 48, 64, 80, 96, 112, 128,
+    /* 32 */ 160, 192, 224, 256,
+    /* 64 */ 320, 384, 448, 512,
+    /* 128 */ 640, 768, 896, 1024,
+    /* 256 */ 1280, 1536, 1792, 2048,
+    /* 512 */ 2560, 3072, 3584, 4096,
+    /* 1024 */ 5120, 6144, 7168, 8192,
+    /* 2048 */ 10240, 12288, 14336, 16384
+};
+
+#define N_SIZE_CLASSES (sizeof(size_classes) / sizeof(size_classes[0]))
+
+int main(void) {
+    void *p[N_SIZE_CLASSES];
+    for (unsigned i = 0; i < N_SIZE_CLASSES; i++) {
+        unsigned size = size_classes[i];
+        p[i] = malloc(size);
+        if (!p) {
+            return 1;
+        }
+        void *q = malloc(size);
+        if (!q) {
+            return 1;
+        }
+        printf("%zu to %zu: %zd\n", size, size, q - p[i]);
+        if (i != 0) {
+            printf("%zu to %zu: %zd\n", size_classes[i - 1], size, p[i - 1] - p[i]);
+        }
+    }
+    return 0;
+}