#pragma once

/* DirectoryEntry
 * |31|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |11|  | 9| 8| 7| 6| 5| 4| 3| 2| 1| 0|
 * |   page table 4-kb aligned address                         | avail  | G| S|  | A| C| W| U| R| P| */
struct __attribute__((packed)) DirectoryEntry {
  unsigned present : 1;   /* 0: if set, the page is actually in physical memory */
  unsigned writeable : 1; /* 1: if set, the page is read/write; otherwise the page is read-only */
  unsigned user : 1;      /* 2: if set, then page can be access by all; otherwise only the supervisor can access it */
  unsigned writethrough : 1; /* 3: if set, write-through caching is enabled; otherwise write-back is enabled instead */
  unsigned cachedisable : 1; /* 4: if set, the page will not be cached */
  unsigned accessed : 1;     /* 5: set by the CPU when the page is read from or written to */
  unsigned dirty : 1;        /* 6: used to determine whether a page has been written to */
  unsigned pagesize : 1;     /* 7: page size == 0 */
  unsigned global : 1;
  unsigned int __available__ : 3; /* available to the OS */
  unsigned int address : 20;
};
/* TODO _Static_assert(sizeof(struct DirectoryEntry) == 4, "DirectoryEntry size"); */

/* DirectoryEntry4MB
 * |31|  |  |  |  |  |  |  |  |22|21|20|  |  |  |  |  |  |13|12|11|  | 9| 8| 7| 6| 5| 4| 3| 2| 1| 0|
 * |   bits 31-22 of address     |RS|   bits 39-22 of       |AT| avail  | G|PS| D| A|CD|WT|US|RW| P|
 * |                             |VD|   address */
struct __attribute__((packed)) DirectoryEntry4MB {
  unsigned present : 1;    /* 0: if set, the page is actually in physical memory */
  unsigned writeable : 1;  /* 1: if set, the page is read/write; otherwise the page is read-only */
  unsigned useraccess : 1; /* 2: if set, then page can be access by all; otherwise only the supervisor can access it */
  unsigned writethrough : 1;  /* 3: if set, write-through caching is enabled; otherwise write-back is enabled instead */
  unsigned cachedisable : 1;  /* 4: if set, the page will not be cached */
  unsigned accessed : 1;      /* 5: set by the CPU when the page is read from or written to */
  unsigned dirty : 1;         /* 6: used to determine whether a page has been written to */
  unsigned pagesize : 1;      /* 7: page size == 1 */
  unsigned global : 1;        /* 8: */
  unsigned __available__ : 3; /* 11..9 available to the OS */
  unsigned pat : 1;           /* 12: page attribute table */
  unsigned int address_high : 8;
  unsigned rsvd : 1; /* 21 */
  unsigned int address_low : 10;
};
/* TODO _Static_assert(sizeof(struct DirectoryEntry4MB) == 4, "DirectoryEntry4M size"); */

/* TableEntry
 * |31|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |11|  | 9| 8| 7| 6| 5| 4| 3| 2| 1| 0|
 * |   page table 4-kb aligned address                         | avail  | G|  | D| A| C| W|US|RW| P| */
struct __attribute__((packed)) TableEntry {
  unsigned present : 1;      /* if set, the page is actually in physical memory */
  unsigned writeable : 1;    /* if set, the page is read/write; otherwise the page is read-only */
  unsigned user : 1;         /* if set, then page can be access by all; otherwise only the supervisor can access it */
  unsigned writethrough : 1; /* if set, write-through caching is enabled; otherwise write-back is enabled instead */
  unsigned cachedisable : 1; /* if set, the page will not be cached */
  unsigned accessed : 1;     /* set by the CPU when the page is read from or written to */
  unsigned dirty : 1;        /* used to determine whether a page has been written to */
  unsigned pat : 1;          /* page attribute table? */
  unsigned global : 1;
  unsigned int __available__ : 3; /* available to the OS */
  unsigned int address : 20;
};
/* TODO _Static_assert(sizeof(struct TableEntry) == 4, "TableEntry size"); */