+ * The following macros optimize certain frequently calculated
+ * quantities by using shifts and masks in place of divisions
+ * modulos and multiplications.
+ */
+#define blkoff(fs, loc) /* calculates (loc % fs->fs_bsize) */ \
+ ((loc) & ~(fs)->fs_bmask)
+#define fragoff(fs, loc) /* calculates (loc % fs->fs_fsize) */ \
+ ((loc) & ~(fs)->fs_fmask)
+#define lblkno(fs, loc) /* calculates (loc / fs->fs_bsize) */ \
+ ((loc) >> (fs)->fs_bshift)
+#define numfrags(fs, loc) /* calculates (loc / fs->fs_fsize) */ \
+ ((loc) >> (fs)->fs_fshift)
+#define blkroundup(fs, size) /* calculates roundup(size, fs->fs_bsize) */ \
+ (((size) + (fs)->fs_bsize - 1) & (fs)->fs_bmask)
+#define fragroundup(fs, size) /* calculates roundup(size, fs->fs_fsize) */ \
+ (((size) + (fs)->fs_fsize - 1) & (fs)->fs_fmask)
+#define fragstoblks(fs, frags) /* calculates (frags / fs->fs_frag) */ \
+ ((frags) >> (fs)->fs_fragshift)
+#define blkstofrags(fs, blks) /* calculates (blks * fs->fs_frag) */ \
+ ((blks) << (fs)->fs_fragshift)
+#define fragnum(fs, fsb) /* calculates (fsb % fs->fs_frag) */ \
+ ((fsb) & ((fs)->fs_frag - 1))
+#define blknum(fs, fsb) /* calculates rounddown(fsb, fs->fs_frag) */ \
+ ((fsb) &~ ((fs)->fs_frag - 1))
+
+/*
+ * Determine the number of available frags given a
+ * percentage to hold in reserve
+ */
+#define freespace(fs, percentreserved) \
+ (blkstofrags((fs), (fs)->fs_cstotal.cs_nbfree) + \
+ (fs)->fs_cstotal.cs_nffree - ((fs)->fs_dsize * (percentreserved) / 100))
+
+/*
+ * Determining the size of a file block in the file system.