Freestanding bitmap.HEADmaster

Functions for individual and contiguous allocations, fills, and clears

2 files changed, 342 insertions, 0 deletions

diff --git a/bitmap.c b/bitmap.c
new file mode 100644
index 0000000..cdc1b46
--- /dev/null
+++ b/bitmap.c
@@ -0,0 +1,230 @@
+#include "bitmap.h"
+
+#define BITMAP_MASK_FULL (~((bmcell_t)0))
+
+#define BITMAP_CELL_SIZE (sizeof(bmcell_t) * 8)
+#define BITMAP_CELL_SHIFT 6
+#define BITMAP_SUBCELL_SHIFT 3
+
+#define BITMAP_TEST(map, i) (map[i >> BITMAP_CELL_SHIFT] & (((bmcell_t)1) << i))
+#define BITMAP_SET(map, i)  (map[i >> BITMAP_CELL_SHIFT] |= (((bmcell_t)1) << i))
+#define BITMAP_USET(map, i) (map[i >> BITMAP_CELL_SHIFT] &= ~(((bmcell_t)1) << i))
+
+void
+bmvl_setup(struct bitmap_vl *bm, size_t bits)
+{
+    bm->head.length = bm->head.bits_free = bits;
+    bm->head.last_free = 0;
+    for(size_t i = 0; i < (bits / BITMAP_BITS_PER_CELL); i++) {
+        bm->cells[i] = 0;
+    }
+}
+
+bool 
+__bm_test(bmcell_t *cells, size_t i)
+{
+    return BITMAP_TEST(cells, i) != 0;
+}
+
+bm_signed_t
+__bm_take(struct bitmap_head *head, bmcell_t *cells)
+{
+    /*Definitely OOM*/
+    if(head->bits_free == 0) return -1;
+    /*If last_free is already free, we can just return that*/
+    if(BITMAP_TEST(cells, head->last_free) == 0) {
+        BITMAP_SET(cells, head->last_free);
+        return head->last_free++;
+    }
+
+    /*Search all cells after last_free if last_free was taken. 
+     * It could mean we're OOM, or that we've missed a gap somewhere*/
+    for(size_t cell = (head->last_free >> BITMAP_CELL_SHIFT);
+            cell < (head->length >> BITMAP_CELL_SHIFT);
+            cell++)
+    {
+        /*A full bitmask means that every bit in the cell is taken*/
+        if(cells[cell] == BITMAP_MASK_FULL) continue;
+
+        /*We sub-divide the search into bytes, so that we can take advantage
+         * of mask searches*/
+        uint8_t *subcells = (uint8_t*)(&cells[cell]);
+        for(uint8_t subcell = 0; subcell < 8; subcell++) {
+            /*If the byte is full, we search the next byte*/
+            if(subcells[subcell] == 0xFF) continue;
+            /*A per-bit search is necessary to find the exact free bit*/
+            for(uint8_t bit = 0; bit < 8; bit++) {
+                if(subcells[subcell] & (1 << bit)) continue;
+                /*Mark the bit as taken*/
+                subcells[subcell] |= ((bmcell_t)1 << bit);
+
+                /*Because we're operating on pow2, we can use bitshifts to
+                 * simplify 2^x.
+                 * Since subcell and bit can only be 1-7, we can OR it into
+                 * the shifted cell value*/
+                head->last_free =
+                    (cell << BITMAP_CELL_SHIFT) |
+                    (subcell << BITMAP_SUBCELL_SHIFT) |
+                    bit;
+                /*This returns the last_free, then increments so that the next
+                 * call can (possibly) get a free value*/
+                head->bits_free--;
+                return head->last_free++;
+            }
+        }
+    }
+    /*Getting here means the bitmap couldn't find a free bit and we are
+     * presumably OOM*/
+    return -1;
+}
+
+bm_signed_t
+__bm_take_contig(struct bitmap_head *head, bmcell_t *cells, size_t l)
+{
+    /*If the bitmap doesn't have enough free bits for the span, it will never
+     * have enough contiguous bits*/
+    if(head->bits_free < l) return -1;
+    /*Simul completion flag and utility value for calculating offsets for return
+     * value*/
+    size_t left = l;
+    for(size_t cell = (head->last_free >> BITMAP_CELL_SHIFT);
+            cell < (head->length >> BITMAP_CELL_SHIFT);
+            cell++)
+    {
+        /*Return case for breakout when we find the contig span*/
+        if(left == 0) break;
+        /*If the bitmask is full, there won't be room to fit the requested span*/
+        if(cells[cell] == BITMAP_MASK_FULL) {
+            left = l;
+            continue;
+        }
+        /*If the bitmask is 0, there are atleast BITMAP_CELL_SIZE contig bits
+         * in the bitmap starting here*/
+        if(cells[cell] == 0) {
+            /*Only continue the loop if there aren't enough bits in this current
+             * cell.*/
+            if(left > BITMAP_CELL_SIZE) {
+                left -= BITMAP_CELL_SIZE;
+                continue;
+            }
+            /*Because there was room for the rest of the span, we can return
+             * this address without worrying about fetching other bits.
+             * The cell index is subtracted by the inverse of left*/
+            head->last_free = 
+                (cell << BITMAP_CELL_SHIFT) - (l - left);
+            /*Mark left so that we break out of this loop and call the proper
+             * return function*/
+            left = 0;
+            break;
+        }
+        /*Divide search into bytes for faster search of bmcell_t structure*/
+        uint8_t *subcells = (uint8_t*)(&cells[cell]);
+        for(uint8_t subcell = 0; subcell < 8; subcell++) {
+            if(left == 0) break;
+            /*Subcell is full, we refill left and stop searching this subcell*/
+            if(subcells[subcell] == 0xFF) {
+                left = l;
+                continue;
+            }
+            /*Since the subcell is empty, there are atleast 8 contig bits*/
+            if(subcells[subcell] == 0) {
+                /*If we need more than 8 bits, we subtract 8 from left and
+                 * continue*/
+                if(left > 8) {
+                    left -= 8;
+                    continue;
+                }
+                /*Otherwise, we return the index of this particular subcell
+                 * minus the inverse of left*/
+                head->last_free = 
+                    ((cell << BITMAP_CELL_SHIFT) |
+                     (subcell << BITMAP_SUBCELL_SHIFT)) -
+                    (l - left);
+                /*Mark left for proper exit and return*/
+                left = 0;
+                break;
+            }
+            /*Search the entire subcell for free bits.*/
+            for(uint8_t bit = 0; bit < 8; bit++) {
+                /*When we find a taken bit, and there are still bits to fetch,
+                 * then the block will never be contiguous and we need to
+                 * start again*/
+                if(subcells[subcell] & (1 << bit)) {
+                    left = l;
+                    continue;
+                }
+                left--;
+                if(left == 0) {
+                    /*When we have found all the bits we need, we return the
+                     * index to the start of the contig span*/
+                    head->last_free =
+                        ((cell << BITMAP_CELL_SHIFT) |
+                         (subcell << BITMAP_SUBCELL_SHIFT) |
+                         bit) -
+                        (l - left);
+                    break;
+                }
+            }
+        }
+    }
+    /*We didn't find a contiguous span. Either the bitmap is fragmented or
+     * there's not enough free space to fit the span*/
+    if(left != 0) return -1;
+
+    /*Mark all of the bits in the span as taken*/
+    for(size_t i = 0; i < l; i++) {
+        BITMAP_SET(cells, (head->last_free + i));
+    }
+    /*Setup to return last_free, while incrementing last_free by l*/
+    head->last_free += l;
+    head->bits_free -= l;
+    return head->last_free - l;
+    
+}
+
+void
+__bm_reserve(struct bitmap_head *head, bmcell_t *cells, size_t i)
+{
+    /*Take the bit at i and update the bits_free counter*/
+    BITMAP_SET(cells, i);
+    head->bits_free--;
+}
+
+void
+__bm_reserve_contig(
+        struct bitmap_head *head, 
+        bmcell_t *cells, 
+        size_t i, 
+        size_t l)
+{
+    /*For every bit between i and i+l, mark as reserved*/
+    head->bits_free -= l;
+    for(; l != 0; l--, i++) {
+        BITMAP_SET(cells, i);
+    }
+}
+
+void
+__bm_release(struct bitmap_head *head, bmcell_t *cells, size_t i)
+{
+    /*Release the bit at i, update last_free, and update the bits_free counter*/
+    BITMAP_USET(cells, i);
+    if(head->last_free > i) head->last_free = i;
+    head->bits_free++;
+}
+
+void 
+__bm_release_contig(
+        struct bitmap_head *head, 
+        bmcell_t *cells, 
+        size_t i, 
+        size_t l)
+{
+    /*Update the last_free and bits_free counters*/
+    head->bits_free += i;
+    if(head->last_free > i) head->last_free = i;
+    /*For every bit between i and i+l, mark as free*/
+    for(; l != 0; l--, i++) {
+        BITMAP_USET(cells, i);
+    }
+}
diff --git a/bitmap.h b/bitmap.h
new file mode 100644
index 0000000..913f818
--- /dev/null
+++ b/bitmap.h
@@ -0,0 +1,112 @@
+/**
+ * bitmap.h
+ * Copyright (c) 2022 Jon Santmyer <jon@jonsantmyer.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * A freestanding implementation of a variable length bitmap.
+ * Depends on compiler provided header files
+ * stdint, stddef, stdbool
+ *
+ *  Allocation for bitmap_vl is dependent on allocator implementation
+ *  Static length bitmaps can be defined using this example
+ *
+ *  struct bitmap_sl
+ *  {
+ *      struct bitmap_head head;
+ *      bmcell_t cells[BITMAP_CELLS(n)];
+ *  };
+ *  where n is the number of bits you want in the bitmap
+ *  To use said struct, you need to feed bmvl_setup with a cast pointer to
+ *  bitmap_sl and the number of bits you have.
+ *
+ *  For other bit systems, replace the type defined as 
+ *  bm_signed_t and bm_unsigned_t
+ *  with an (u)int_t type of the proper bit length
+ *  
+ *  For using the bitmap, use the functions declared under #define blocks.
+ *  The hidden functions are for genericising other bitmap types following
+ *  the above format.
+ *
+ *  bitmap_head contains a last_free variable which is used to accelerate the
+ *  average allocation times. Instead of iterating through the entire map, the
+ *  allocator can iterate from last_free until length.
+ *  Most bm_take operations will be O(1) because last_free is assumed to mark an
+ *  empty bit in the map
+ */
+
+#ifndef BITMAP_H
+#define BITMAP_H 1
+
+#include <stdint.h>
+#include <stddef.h>
+#include <stdbool.h>
+
+/*Can be changed to int32_t/uint32_t for 32-bit systems*/
+typedef int64_t bm_signed_t;
+typedef uint64_t bm_unsigned_t;
+typedef bm_unsigned_t bmcell_t;
+
+struct bitmap_head
+{
+    size_t length;
+    size_t bits_free;
+    size_t last_free;
+};
+
+struct bitmap_vl
+{
+    struct bitmap_head head;
+    bmcell_t cells[];
+};
+
+#define BITMAP_BITS_PER_CELL (8 * sizeof(bmcell_t))
+#define BITMAP_CELLS(bits) \
+    ((bits + (BITMAP_BITS_PER_CELL - 1)) / (BITMAP_BITS_PER_CELL))
+#define BITMAP_LEN(bits) ((bits / 8) + (sizeof(struct bitmap_head)))
+
+/*Fills a bitmap struct with proper length, and status vars. Zeros the cells*/
+void bmvl_setup(struct bitmap_vl *bm, size_t bits);
+
+/*Check if bit in bitmap is taken*/
+bool __bm_test(bmcell_t *cells, size_t i);
+#define bm_test(bitmap, i) __bm_test(bitmap->cells, i)
+
+/*Functions for taking free bits in the bitmap. Returns -1 if none are
+ * available. Returns the index of the (first) bit if a suitable range is found
+ */
+bm_signed_t __bm_take(struct bitmap_head *head, bmcell_t *cells);
+bm_signed_t __bm_take_contig(struct bitmap_head *head, bmcell_t *cells, size_t l);
+#define bm_take(bitmap) __bm_take(&bitmap->head, bitmap->cells)
+#define bm_take_contig(bitmap, l) \
+    __bm_take_contig(&bitmap->head, bitmap->cells, l)
+
+/* Fills the bit/bits at i. Runs until l if applicable */
+void __bm_reserve(struct bitmap_head *head, bmcell_t *cells, size_t i);
+void __bm_reserve_contig(struct bitmap_head *head, bmcell_t *cells, size_t i, size_t l);
+#define bm_reserve(bitmap, i) __bm_reserve(&bitmap->head, bitmap->cells, i)
+#define bm_reserve_contig(bitmap, i, l) __bm_reserve_contig(&bitmap->head, bitmap->cells, i, l)
+
+/* Clears the bit/bits at i. Runs until l if applicable */
+void __bm_release(struct bitmap_head *head, bmcell_t *cells, size_t i);
+void __bm_release_contig(struct bitmap_head *head, bmcell_t *cells, size_t i, size_t l);
+#define bm_release(bitmap, i) __bm_release(&bitmap->head, bitmap->cells, i)
+#define bm_release_contig(bitmap, i, l) __bm_release_contig(&bitmap->head, bitmap->cells, i, l)
+
+#endif