Initial Spring 2016 commit.

kern/lib/bitmap.c

@@ -0,0 +1,176 @@
+/*
+ * Copyright (c) 2000, 2001, 2002
+ *	The President and Fellows of Harvard College.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * Fixed-size array of bits. (Intended for storage management.)
+ */
+
+#include <types.h>
+#include <kern/errno.h>
+#include <lib.h>
+#include <bitmap.h>
+
+/*
+ * It would be a lot more efficient on most platforms to use uint32_t
+ * or unsigned long as the base type for holding bits. But we don't,
+ * because if one uses any data type more than a single byte wide,
+ * bitmap data saved on disk becomes endian-dependent, which is a
+ * severe nuisance.
+ */
+#define BITS_PER_WORD   (CHAR_BIT)
+#define WORD_TYPE       unsigned char
+#define WORD_ALLBITS    (0xff)
+
+struct bitmap {
+        unsigned nbits;
+        WORD_TYPE *v;
+};
+
+
+struct bitmap *
+bitmap_create(unsigned nbits)
+{
+        struct bitmap *b;
+        unsigned words;
+
+        words = DIVROUNDUP(nbits, BITS_PER_WORD);
+        b = kmalloc(sizeof(struct bitmap));
+        if (b == NULL) {
+                return NULL;
+        }
+        b->v = kmalloc(words*sizeof(WORD_TYPE));
+        if (b->v == NULL) {
+                kfree(b);
+                return NULL;
+        }
+
+        bzero(b->v, words*sizeof(WORD_TYPE));
+        b->nbits = nbits;
+
+        /* Mark any leftover bits at the end in use */
+        if (words > nbits / BITS_PER_WORD) {
+                unsigned j, ix = words-1;
+                unsigned overbits = nbits - ix*BITS_PER_WORD;
+
+                KASSERT(nbits / BITS_PER_WORD == words-1);
+                KASSERT(overbits > 0 && overbits < BITS_PER_WORD);
+
+                for (j=overbits; j<BITS_PER_WORD; j++) {
+                        b->v[ix] |= ((WORD_TYPE)1 << j);
+                }
+        }
+
+        return b;
+}
+
+void *
+bitmap_getdata(struct bitmap *b)
+{
+        return b->v;
+}
+
+int
+bitmap_alloc(struct bitmap *b, unsigned *index)
+{
+        unsigned ix;
+        unsigned maxix = DIVROUNDUP(b->nbits, BITS_PER_WORD);
+        unsigned offset;
+
+        for (ix=0; ix<maxix; ix++) {
+                if (b->v[ix]!=WORD_ALLBITS) {
+                        for (offset = 0; offset < BITS_PER_WORD; offset++) {
+                                WORD_TYPE mask = ((WORD_TYPE)1) << offset;
+
+                                if ((b->v[ix] & mask)==0) {
+                                        b->v[ix] |= mask;
+                                        *index = (ix*BITS_PER_WORD)+offset;
+                                        KASSERT(*index < b->nbits);
+                                        return 0;
+                                }
+                        }
+                        KASSERT(0);
+                }
+        }
+        return ENOSPC;
+}
+
+static
+inline
+void
+bitmap_translate(unsigned bitno, unsigned *ix, WORD_TYPE *mask)
+{
+        unsigned offset;
+        *ix = bitno / BITS_PER_WORD;
+        offset = bitno % BITS_PER_WORD;
+        *mask = ((WORD_TYPE)1) << offset;
+}
+
+void
+bitmap_mark(struct bitmap *b, unsigned index)
+{
+        unsigned ix;
+        WORD_TYPE mask;
+
+        KASSERT(index < b->nbits);
+        bitmap_translate(index, &ix, &mask);
+
+        KASSERT((b->v[ix] & mask)==0);
+        b->v[ix] |= mask;
+}
+
+void
+bitmap_unmark(struct bitmap *b, unsigned index)
+{
+        unsigned ix;
+        WORD_TYPE mask;
+
+        KASSERT(index < b->nbits);
+        bitmap_translate(index, &ix, &mask);
+
+        KASSERT((b->v[ix] & mask)!=0);
+        b->v[ix] &= ~mask;
+}
+
+
+int
+bitmap_isset(struct bitmap *b, unsigned index)
+{
+        unsigned ix;
+        WORD_TYPE mask;
+
+        bitmap_translate(index, &ix, &mask);
+        return (b->v[ix] & mask);
+}
+
+void
+bitmap_destroy(struct bitmap *b)
+{
+        kfree(b->v);
+        kfree(b);
+}