/* Rflags Register */

/// Carry flag.
pub const RFLAGS_CF: u64 = 1 << 0;
/// Parity flag.
pub const RFLAGS_PF: u64 = 1 << 2;
/// Adjust flag.
pub const RFLAGS_AF: u64 = 1 << 4;
/// Zero flag.
pub const RFLAGS_ZF: u64 = 1 << 6;
/// Sign flag.
pub const RFLAGS_SF: u64 = 1 << 7;
/// Sign flag.
pub const RFLAGS_IF: u64 = 1 << 9;
/// Direction flag.
pub const RFLAGS_DF: u64 = 1 << 10;
/// Overflow flag.
pub const RFLAGS_OF: u64 = 1 << 11;
/// I/O privilege level.
pub const RFLAGS_IOPL: u64 = 0b11 << 12;
/// Alignment check.
pub const RFLAGS_AC: u64 = 1 << 18;

pub const fn rflags_cf(r: u64) -> u64   { (r & RFLAGS_CF)   >> 0 }
pub const fn rflags_pf(r: u64) -> u64   { (r & RFLAGS_PF)   >> 2 }
pub const fn rflags_af(r: u64) -> u64   { (r & RFLAGS_AF)   >> 4 }
pub const fn rflags_zf(r: u64) -> u64   { (r & RFLAGS_ZF)   >> 6 }
pub const fn rflags_sf(r: u64) -> u64   { (r & RFLAGS_SF)   >> 7 }
pub const fn rflags_if(r: u64) -> u64   { (r & RFLAGS_IF)   >> 9 }
pub const fn rflags_df(r: u64) -> u64   { (r & RFLAGS_DF)   >> 10 }
pub const fn rflags_of(r: u64) -> u64   { (r & RFLAGS_OF)   >> 11 }
pub const fn rflags_iopl(r: u64) -> u64 { (r & RFLAGS_IOPL) >> 12 }
pub const fn rflags_ac(r: u64) -> u64   { (r & RFLAGS_AC)   >> 18 }

/* Segment Selector */

/// Requested privilege level.
///
/// Privilege level of the segment selector, where `0` is the most privileged mode and `3` the
/// least.
pub const SEG_SELECTOR_RPL : u16 = 0b11 << 0;
/// Table indicator.
///
/// | TI | Table |
/// |----|-------|
/// | 0  | GDT   |
/// | 1  | LDT   |
pub const SEG_SELECTOR_TI : u16 = 1 << 2;
/// Table index.
///
/// Index into the `GDT` or `LDT` table to select the segment descriptor. `GDT.base + 8 * index`
/// gives the address of the segment descriptor (times `8` because every segment descriptor is `8
/// byte`).
pub const SEG_SELECTOR_INDEX : u16 = 0x1fff << 3;

pub const fn seg_selector_rpl(s : u16) -> u16   { (s & SEG_SELECTOR_RPL)   >> 0 }
pub const fn seg_selector_ti(s : u16) -> u16    { (s & SEG_SELECTOR_TI)    >> 2 }
pub const fn seg_selector_index(s : u16) -> u16 { (s & SEG_SELECTOR_INDEX) >> 3 }

/* Control Register CR0 (operation mode & state of the processor) */

/// Protection Enable.
///
/// Enables `protected mode` when set and `real-address mode` when cleared. This enables
/// `segment-level protection` not paging.
pub const CR0_PE: u64 = 1 << 0;
/// Monitor Coprocessor.
pub const CR0_MP: u64 = 1 << 1;
/// Emulation.
///
/// When set indicates the process does not have a FPU. FPU instructions will generate an exception
/// that software can emulate the instruction.
pub const CR0_EM: u64 = 1 << 2;
/// Task Switched.
pub const CR0_TS: u64 = 1 << 3;
/// Extension Type.
pub const CR0_ET: u64 = 1 << 4;
/// Numeric Error.
pub const CR0_NE: u64 = 1 << 5;
/// Write Protect.
///
/// When set supervisor-level procedures can't write to read-only pages.
pub const CR0_WP: u64 = 1 << 16;
/// Alignment Mask.
///
/// Enables alignment check for `CPL=3`, check is only done if the [AC
/// bit](crate::x86_64::RFLAGS_AC) of the `rflags` register ist set.
pub const CR0_AM: u64 = 1 << 18;
/// Not Write-Torugh.
pub const CR0_NW: u64 = 1 << 29;
/// Cachine disable.
pub const CR0_CD: u64 = 1 << 30;
/// Paging.
///
/// Enables paging when set, requires [CR0_PE](crate::x86_64::CR0_PE) to be set as well.
pub const CR0_PG: u64 = 1 << 31;

/* Control Register CR3 (paging information)
 *
 * Holds the physical base address of the first paging structure. The 12 lower bytes of the base
 * address are assumed to be 0 and hence the first paging structure must be aligned to a 4K
 * boundary.
 */

/// Mask for physical base address of paging structure.
pub const CR3_PAGE_BASE_MASK: u64 = 0xffff_ffff_ffff_0000;

/// Page-level Write-Through.
pub const CR3_PWT: u64 = 1 << 3;
/// Page-level Cache Disable.
pub const CR3_PCD: u64 = 1 << 4;

/* Control Register CR4 (flags for arch extenstions processor capabilities) */

/// Physical Address Extenstion.
///
/// When set enables paging to produce physicall addresses with more than 32 bits. Required before
/// entering `long mode`.
pub const CR4_PAE: u64 = 1 << 5;
/// 57-bit Linear Addresses.
///
/// When set in `long mode` enables `5-level` paging to translate `57-bit` linear addresses. When
/// cleared use `4-level` paging to translate `48-bit` linear addresses.
pub const CR4_LA57: u64 = 1 << 5;

/* Extended Feature Enable Register (EFER) */

pub const MSR_EFER: u64 = 0xc000_0080;

/// Long Mode Enable.
///
/// When set enables long mode operations.
pub const EFER_LME: u64 = 1 << 8;
/// Long Mode Active (readonly).
///
/// When set indicates long mode is active.
pub const EFER_LMA: u64 = 1 << 10;

/* Paging */

/// Page entry present.
pub const PAGE_ENTRY_PRESENT : u64 = 1 << 0;
/// Page region read/write.
///
/// If set, region reference by paging entry is writeable.
pub const PAGE_RENTRY_RW : u64 = 1 << 1;