/* Copyright (c) 2024 Freya Murphy */

#ifndef __MIPS32_H__
#define __MIPS32_H__

#include <stddef.h>
#include <stdint.h>
#include <mlimits.h>

/* all mips registers $0-$31 */
enum mips32_register {
	MIPS32_REG_ZERO =  0,
	MIPS32_REG_AT   =  1,
	MIPS32_REG_V0   =  2,
	MIPS32_REG_V1   =  3,
	MIPS32_REG_A0   =  4,
	MIPS32_REG_A1   =  5,
	MIPS32_REG_A2   =  6,
	MIPS32_REG_A3   =  7,
	MIPS32_REG_T0   =  8,
	MIPS32_REG_T1   =  9,
	MIPS32_REG_T2   = 10,
	MIPS32_REG_T3   = 11,
	MIPS32_REG_T4   = 12,
	MIPS32_REG_T5   = 13,
	MIPS32_REG_T6   = 14,
	MIPS32_REG_T7   = 15,
	MIPS32_REG_S0   = 16,
	MIPS32_REG_S1   = 17,
	MIPS32_REG_S2   = 18,
	MIPS32_REG_S3   = 19,
	MIPS32_REG_S4   = 20,
	MIPS32_REG_S5   = 21,
	MIPS32_REG_S6   = 22,
	MIPS32_REG_S7   = 23,
	MIPS32_REG_T8   = 24,
	MIPS32_REG_T9   = 25,
	MIPS32_REG_K0   = 26,
	MIPS32_REG_K1   = 27,
	MIPS32_REG_GP   = 28,
	MIPS32_REG_SP   = 29,
	MIPS32_REG_FP   = 30,
	MIPS32_REG_RA   = 31,
};

/* mips instruction */
union mips32_instruction {
	/* raw ins */
	uint32_t raw            : 32;
	/* register type */
	struct {
		uint32_t funct  : 6;
		uint32_t shamt  : 5;
		uint32_t rd     : 5;
		uint32_t rt     : 5;
		uint32_t rs     : 5;
		uint32_t op     : 6;
	};
	/* immediate type */
	struct {
		uint32_t immd   : 16;
		uint32_t        : 16;
	};
	/* jump type */
	struct {
		uint32_t target : 26;
		uint32_t        :  6;
	};
	/* branch compact */
	struct {
		 int32_t offs26 : 26;
		uint32_t        :  6;
	};
	/* branch */
	struct {
		 int32_t offset : 16;
		uint32_t bfunct :  5;
		uint32_t        : 11;
	};
} __attribute__((packed));

/// grammer syntax:
///
/// ... the grammer takes entries parsed from the instruction,
/// and updates the instructions with values based on the type
/// of entry. i.e. immd would require a immd in the next argument,
/// and update the low 16bits of the instruction.
///
/// GRAMMER -> ENTRIES
/// GRAMMER -> ε
/// ENTRIES -> ENTRIES, ENTRY
/// ENTRY   -> rd           // i.e. $at
/// ENTRY   -> rs
/// ENTRY   -> rt
/// ENTRY   -> immd         // i.e. 0x80
/// ENTRY   -> offset       // i.e. main (16bits)
/// ENTRY   -> offest(base) // i.e. 4($sp)
/// ENTRY   -> target       // i.e. main (28bits shifted)
///
/// // grammer entries are always defined onto themselves... meaning the
/// // name of their type directly corresponds to the mips field in the
/// // instruction
///
/// pseudo grammer syntax:
///
/// ... psuedo entries represents what values should be placed where
/// in each of the pseudo instructions. psuedo grammer is extended such
/// that hardcoded values can be returned. i.e. setting rt=$at
///
/// GRAMMER  -> ENTRIES
/// GRAMMER  -> ε
/// ENTREIS  -> ENTRIES, ENTRYSET
/// ENTRYSET -> ENTRY | SET
/// SET      -> ENTRY = <REGISTER>
/// ENTRY    -> <GRAMMER: ENTRY> // i.e. any valid entry from grammer synax
/// ENTRY    -> hi // high 16bits of <target> into <immd>
/// ENTRY    -> lo // low 16bits of <target> into <immd>

/* mips grammer */
struct mips32_grammer {
	// the name of the ins
	char *name;
	// the grammer of the ins
	char *grammer;
	// the index of the ins (if real)
	int enum_index;

	// for pseudo instructions only
	int pseudo_len;
	struct mips32__pseudo_grammer {
		// what instruction is this
		// part in the pseudo instruction
		int enum_index;
		// what parts of the instruction
		// to update with values from
		// grammer
		char *update;

	} pseudo_grammer[MAX_ARG_LENGTH];
};

#endif /* __MIPS32_H__ */