X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Flib%2Fkernel%2Fbitmap.c;h=77edf2270b35435538fbbb5adeec52096403f50b;hb=468f548e6848498767eb6ac7b55ab9bca06de462;hp=7bbc92868ca9fdf908798c919c168c7b3b44732b;hpb=f2f8875638593bd5365cfd6a5ba7c9578e52322f;p=pintos-anon

diff --git a/src/lib/kernel/bitmap.c b/src/lib/kernel/bitmap.c
index 7bbc928..77edf22 100644
--- a/src/lib/kernel/bitmap.c
+++ b/src/lib/kernel/bitmap.c
@@ -1,6 +1,7 @@
 #include "bitmap.h"
 #include <debug.h>
 #include <limits.h>
+#include <random.h>
 #include <round.h>
 #include <stdio.h>
 #include "threads/malloc.h"
@@ -8,9 +9,28 @@
 #include "filesys/file.h"
 #endif
 
+/* Element type.
+
+   This must be an unsigned integer type at least as wide as int.
+
+   Each bit represents one bit in the bitmap.
+   If bit 0 in an element represents bit K in the bitmap,
+   then bit 1 in the element represents bit K+1 in the bitmap,
+   and so on. */
+typedef unsigned long elem_type;
+
 /* Number of bits in an element. */
 #define ELEM_BITS (sizeof (elem_type) * CHAR_BIT)
 
+/* From the outside, a bitmap is an array of bits.  From the
+   inside, it's an array of elem_type (defined above) that
+   simulates an array of bits. */
+struct bitmap
+  {
+    size_t bit_cnt;     /* Number of bits. */
+    elem_type *bits;    /* Elements that represent bits. */
+  };
+
 /* Returns the index of the element that contains the bit
    numbered BIT_IDX. */
 static inline size_t
@@ -27,18 +47,18 @@ bit_mask (size_t bit_idx)
   return (elem_type) 1 << (bit_idx % ELEM_BITS);
 }
 
-/* Returns the number of elements required for B's bits. */
+/* Returns the number of elements required for BIT_CNT bits. */
 static inline size_t
-elem_cnt (const struct bitmap *b) 
+elem_cnt (size_t bit_cnt)
 {
-  return DIV_ROUND_UP (b->bit_cnt, ELEM_BITS);
+  return DIV_ROUND_UP (bit_cnt, ELEM_BITS);
 }
 
-/* Returns the number of bytes required by B's elements. */
+/* Returns the number of bytes required for BIT_CNT bits. */
 static inline size_t
-byte_cnt (const struct bitmap *b) 
+byte_cnt (size_t bit_cnt)
 {
-  return sizeof (elem_type) * elem_cnt (b);
+  return sizeof (elem_type) * elem_cnt (bit_cnt);
 }
 
 /* Returns a bit mask in which the bits actually used in the last
@@ -50,29 +70,68 @@ last_mask (const struct bitmap *b)
   return last_bits ? ((elem_type) 1 << last_bits) - 1 : (elem_type) -1;
 }
 
-/* Initializes B to be a bitmap of BIT_CNT bits.
-   Returns true if successfalse, false if memory allocation
+/* Creation and destruction. */
+
+/* Initializes B to be a bitmap of BIT_CNT bits
+   and sets all of its bits to false.
+   Returns true if success, false if memory allocation
    failed. */
-bool
-bitmap_init (struct bitmap *b, size_t bit_cnt) 
+struct bitmap *
+bitmap_create (size_t bit_cnt) 
 {
-  b->bit_cnt = bit_cnt;
-  b->bits = malloc (byte_cnt (b));
-  if (b->bits == NULL && bit_cnt > 0) 
-    return false;
+  struct bitmap *b = malloc (sizeof *b);
+  if (b != NULL)
+    {
+      b->bit_cnt = bit_cnt;
+      b->bits = malloc (byte_cnt (bit_cnt));
+      if (b->bits != NULL || bit_cnt == 0)
+        {
+          bitmap_set_all (b, false);
+          return b;
+        }
+      free (b);
+    }
+  return NULL;
+}
 
+/* Creates and returns a bitmap with BIT_CNT bits in the
+   BLOCK_SIZE bytes of storage preallocated at BLOCK.
+   BLOCK_SIZE must be at least bitmap_needed_bytes(BIT_CNT). */
+struct bitmap *
+bitmap_create_in_buf (size_t bit_cnt, void *block, size_t block_size UNUSED)
+{
+  struct bitmap *b = block;
+  
+  ASSERT (block_size >= bitmap_buf_size (bit_cnt));
+
+  b->bit_cnt = bit_cnt;
+  b->bits = (elem_type *) (b + 1);
   bitmap_set_all (b, false);
-  return true;
+  return b;
+}
+
+/* Returns the number of bytes required to accomodate a bitmap
+   with BIT_CNT bits (for use with bitmap_create_in_buf()). */
+size_t
+bitmap_buf_size (size_t bit_cnt) 
+{
+  return sizeof (struct bitmap) + byte_cnt (bit_cnt);
 }
 
-/* Destroys bitmap B, freeing its storage. */
+/* Destroys bitmap B, freeing its storage.
+   Not for use on bitmaps created by
+   bitmap_create_preallocated(). */
 void
 bitmap_destroy (struct bitmap *b) 
 {
-  ASSERT (b);
-  
-  free (b->bits);
+  if (b != NULL) 
+    {
+      free (b->bits);
+      free (b);
+    }
 }
+
+/* Bitmap size. */
 
 /* Returns the number of bits in B. */
 size_t
@@ -80,58 +139,60 @@ bitmap_size (const struct bitmap *b)
 {
   return b->bit_cnt;
 }
+
+/* Setting and testing single bits. */
 
-/* Sets the bit numbered IDX in B to VALUE. */
+/* Atomically sets the bit numbered IDX in B to VALUE. */
 void
 bitmap_set (struct bitmap *b, size_t idx, bool value) 
 {
   ASSERT (b != NULL);
   ASSERT (idx < b->bit_cnt);
   if (value)
-    b->bits[elem_idx (idx)] |= bit_mask (idx);
+    bitmap_mark (b, idx);
   else
-    b->bits[elem_idx (idx)] &= ~bit_mask (idx);
+    bitmap_reset (b, idx);
 }
 
-/* Sets all bits in B to VALUE. */
+/* Atomically sets the bit numbered BIT_IDX in B to true. */
 void
-bitmap_set_all (struct bitmap *b, bool value) 
+bitmap_mark (struct bitmap *b, size_t bit_idx) 
 {
-  size_t i;
-  
-  ASSERT (b != NULL);
+  size_t idx = elem_idx (bit_idx);
+  elem_type mask = bit_mask (bit_idx);
 
-  if (b->bit_cnt > 0)
-    {
-      for (i = 0; i < elem_cnt (b); i++)
-        b->bits[i] = value ? (elem_type) -1 : 0;
-      b->bits[elem_cnt (b) - 1] &= last_mask (b); 
-    }
+  /* This is equivalent to `b->bits[idx] |= mask' except that it
+     is guaranteed to be atomic on a uniprocessor machine.  See
+     the description of the OR instruction in [IA32-v2b]. */
+  asm ("orl %1, %0" : "=m" (b->bits[idx]) : "r" (mask) : "cc");
 }
 
-/* Sets the bit numbered IDX in B to true. */
+/* Atomically sets the bit numbered BIT_IDX in B to false. */
 void
-bitmap_mark (struct bitmap *b, size_t idx) 
+bitmap_reset (struct bitmap *b, size_t bit_idx) 
 {
-  bitmap_set (b, idx, true);
-}
+  size_t idx = elem_idx (bit_idx);
+  elem_type mask = bit_mask (bit_idx);
 
-/* Sets the bit numbered IDX in B to false. */
-void
-bitmap_reset (struct bitmap *b, size_t idx) 
-{
-  bitmap_set (b, idx, false);
+  /* This is equivalent to `b->bits[idx] &= ~mask' except that it
+     is guaranteed to be atomic on a uniprocessor machine.  See
+     the description of the AND instruction in [IA32-v2a]. */
+  asm ("andl %1, %0" : "=m" (b->bits[idx]) : "r" (~mask) : "cc");
 }
 
-/* Toggles the bit numbered IDX in B;
+/* Atomically toggles the bit numbered IDX in B;
    that is, if it is true, makes it false,
    and if it is false, makes it true. */
 void
-bitmap_flip (struct bitmap *b, size_t idx) 
+bitmap_flip (struct bitmap *b, size_t bit_idx) 
 {
-  ASSERT (b != NULL);
-  ASSERT (idx < b->bit_cnt);
-  b->bits[elem_idx (idx)] ^= bit_mask (idx);
+  size_t idx = elem_idx (bit_idx);
+  elem_type mask = bit_mask (bit_idx);
+
+  /* This is equivalent to `b->bits[idx] ^= mask' except that it
+     is guaranteed to be atomic on a uniprocessor machine.  See
+     the description of the XOR instruction in [IA32-v2b]. */
+  asm ("xorl %1, %0" : "=m" (b->bits[idx]) : "r" (mask) : "cc");
 }
 
 /* Returns the value of the bit numbered IDX in B. */
@@ -142,159 +203,176 @@ bitmap_test (const struct bitmap *b, size_t idx)
   ASSERT (idx < b->bit_cnt);
   return (b->bits[elem_idx (idx)] & bit_mask (idx)) != 0;
 }
+
+/* Setting and testing multiple bits. */
 
-/* Returns the smallest index of a bit set to VALUE in B.
-   If no bits in B are set to VALUE, returns BITMAP_ERROR. */
-size_t
-bitmap_scan (const struct bitmap *b, bool value) 
+/* Sets all bits in B to VALUE. */
+void
+bitmap_set_all (struct bitmap *b, bool value) 
 {
-  elem_type ignore = value ? 0 : (elem_type) -1;
-  size_t idx;
-  
   ASSERT (b != NULL);
-  for (idx = 0; idx < elem_cnt (b); idx++)
-    {
-      elem_type e = b->bits[idx];
-      if (e != ignore)
-        {
-          idx *= ELEM_BITS;
-
-          while ((e & 1) != value)
-            {
-              e >>= 1;
-              idx++;
-            }
 
-          return idx < b->bit_cnt ? idx : BITMAP_ERROR;
-        }
-    }
-  return BITMAP_ERROR;
+  bitmap_set_multiple (b, 0, bitmap_size (b), value);
 }
 
-/* Finds the smallest index of a bit set to false in B,
-   sets it to true, and returns the index.
-   If no bits in B are set to false, changes no bits and
-   returns BITMAP_ERROR. */
-size_t
-bitmap_find_and_set (struct bitmap *b) 
+/* Sets the CNT bits starting at START in B to VALUE. */
+void
+bitmap_set_multiple (struct bitmap *b, size_t start, size_t cnt, bool value) 
 {
-  size_t idx = bitmap_scan (b, false);
-  if (idx != BITMAP_ERROR) 
-    bitmap_mark (b, idx);
-  return idx;
-}
+  size_t i;
+  
+  ASSERT (b != NULL);
+  ASSERT (start <= b->bit_cnt);
+  ASSERT (start + cnt <= b->bit_cnt);
 
-/* Finds the smallest index of a bit set to true in B,
-   sets it to false, and returns the index.
-   If no bits in B are set to true, changes no bits and
-   returns BITMAP_ERROR. */
-size_t
-bitmap_find_and_clear (struct bitmap *b) 
-{
-  size_t idx = bitmap_scan (b, true);
-  if (idx != BITMAP_ERROR) 
-    bitmap_reset (b, idx);
-  return idx;
+  for (i = 0; i < cnt; i++)
+    bitmap_set (b, start + i, value);
 }
 
-/* Returns the number of bits in B set to true. */
+/* Returns the number of bits in B between START and START + CNT,
+   exclusive, that are set to VALUE. */
 size_t
-bitmap_set_cnt (const struct bitmap *b) 
+bitmap_count (const struct bitmap *b, size_t start, size_t cnt, bool value) 
 {
-  size_t cnt;
-  size_t i;
+  size_t i, value_cnt;
 
   ASSERT (b != NULL);
-  cnt = 0;
-  for (i = 0; i < elem_cnt (b); i++)
-    {
-      elem_type e = b->bits[i];
-      while (e != 0) 
-        {
-          cnt++;
-          e &= e - 1;
-        }
-    }
-  return cnt;
+  ASSERT (start <= b->bit_cnt);
+  ASSERT (start + cnt <= b->bit_cnt);
+
+  value_cnt = 0;
+  for (i = 0; i < cnt; i++)
+    if (bitmap_test (b, start + i) == value)
+      value_cnt++;
+  return value_cnt;
 }
 
-/* Returns true if any bits in B are set to true,
-   and false otherwise.*/
+/* Returns true if any bits in B between START and START + CNT,
+   exclusive, are set to VALUE, and false otherwise. */
 bool
-bitmap_any (const struct bitmap *b) 
+bitmap_contains (const struct bitmap *b, size_t start, size_t cnt, bool value) 
 {
   size_t i;
-
+  
   ASSERT (b != NULL);
-  for (i = 0; i < elem_cnt (b); i++)
-    if (b->bits[i])
+  ASSERT (start <= b->bit_cnt);
+  ASSERT (start + cnt <= b->bit_cnt);
+
+  for (i = 0; i < cnt; i++)
+    if (bitmap_test (b, start + i) == value)
       return true;
   return false;
 }
 
-/* Returns the number of bits in B set to false. */
+/* Returns true if any bits in B between START and START + CNT,
+   exclusive, are set to true, and false otherwise.*/
 bool
-bitmap_clear_cnt (const struct bitmap *b) 
+bitmap_any (const struct bitmap *b, size_t start, size_t cnt) 
 {
-  return b->bit_cnt - bitmap_set_cnt (b);
+  return bitmap_contains (b, start, cnt, true);
 }
 
-/* Returns true if no bits in B are set to true,
-   and false otherwise.*/
+/* Returns true if no bits in B between START and START + CNT,
+   exclusive, are set to true, and false otherwise.*/
 bool
-bitmap_none (const struct bitmap *b) 
+bitmap_none (const struct bitmap *b, size_t start, size_t cnt) 
 {
-  return !bitmap_any (b); 
+  return !bitmap_contains (b, start, cnt, true);
 }
 
-/* Returns true if every bit in B is set to true,
-   and false otherwise. */
+/* Returns true if every bit in B between START and START + CNT,
+   exclusive, is set to true, and false otherwise. */
 bool
-bitmap_all (const struct bitmap *b) 
+bitmap_all (const struct bitmap *b, size_t start, size_t cnt) 
 {
-  size_t i;
+  return !bitmap_contains (b, start, cnt, false);
+}
+
+/* Finding set or unset bits. */
 
+/* Finds and returns the starting index of a group of CNT
+   consecutive bits in B at or after START that are all set to
+   VALUE.
+   If there is no such group, returns BITMAP_ERROR. */
+size_t
+bitmap_scan (const struct bitmap *b, size_t start, size_t cnt, bool value) 
+{
   ASSERT (b != NULL);
+  ASSERT (start <= b->bit_cnt);
 
-  if (b->bit_cnt == 0)
-    return true;
-  
-  for (i = 0; i < elem_cnt (b) - 1; i++)
-    if (b->bits[i] != (elem_type) -1)
-      return false;
-  return b->bits[i] == last_mask (b);
+  if (cnt <= b->bit_cnt) 
+    {
+      size_t last = b->bit_cnt - cnt;
+      size_t middle = start + random_ulong () % (last - start + 1); 
+      size_t i = middle;
+      do
+        {
+          if (!bitmap_contains (b, i, cnt, !value))
+            return i; 
+          i = i != last ? i + 1 : start;
+        }
+      while (i != middle);
+    }
+  return BITMAP_ERROR;
+}
+
+/* Finds a group of CNT consecutive bits in B at or after
+   START that are all set to VALUE, flips them all to !VALUE,
+   and returns the index of the first bit in the group.
+   If there is no such group, returns BITMAP_ERROR.
+   If CNT is zero, returns 0.
+   Bits are set atomically, but testing bits is not atomic with
+   setting them. */
+size_t
+bitmap_scan_and_flip (struct bitmap *b, size_t start, size_t cnt, bool value)
+{
+  size_t idx = bitmap_scan (b, start, cnt, value);
+  if (idx != BITMAP_ERROR) 
+    bitmap_set_multiple (b, idx, cnt, !value);
+  return idx;
 }
+
+/* File input and output. */
 
 #ifdef FILESYS
 /* Returns the number of bytes needed to store B in a file. */
 size_t
 bitmap_file_size (const struct bitmap *b) 
 {
-  return byte_cnt (b);
+  return byte_cnt (b->bit_cnt);
 }
 
-/* Reads FILE into B, ignoring errors. */
-void
+/* Reads B from FILE.  Returns true if successful, false
+   otherwise. */
+bool
 bitmap_read (struct bitmap *b, struct file *file) 
 {
+  bool success = true;
   if (b->bit_cnt > 0) 
     {
-      file_read_at (file, b->bits, byte_cnt (b), 0);
-      b->bits[elem_cnt (b) - 1] &= last_mask (b);
+      off_t size = byte_cnt (b->bit_cnt);
+      success = file_read_at (file, b->bits, size, 0) == size;
+      b->bits[elem_cnt (b->bit_cnt) - 1] &= last_mask (b);
     }
+  return success;
 }
 
-/* Writes FILE to B, ignoring errors. */
-void
+/* Writes B to FILE.  Return true if successful, false
+   otherwise. */
+bool
 bitmap_write (const struct bitmap *b, struct file *file)
 {
-  file_write_at (file, b->bits, byte_cnt (b), 0);
+  off_t size = byte_cnt (b->bit_cnt);
+  return file_write_at (file, b->bits, size, 0) == size;
 }
 #endif /* FILESYS */
+
+/* Debugging. */
 
 /* Dumps the contents of B to the console as hexadecimal. */
 void
 bitmap_dump (const struct bitmap *b) 
 {
-  hex_dump (b->bits, byte_cnt (b), false);
+  hex_dump (0, b->bits, byte_cnt (b->bit_cnt), false);
 }
+