#include "instr.h"

// Gets the immediate bits, clearing others and shifting right.
uint32_t get_i(const uint32_t instr) { return instr & IMMEDIATE_BITS; }

// Gets the pattern bits, clearing others and shifting right.
uint32_t get_p(const uint32_t instr) { return (instr & PATTERN_BITS) >> 26; }

// Gets the d bits, clearing others and shifting right.
uint32_t get_d(const uint32_t instr) { return (instr & D_BITS) >> 11; }

// Gets the t bits, clearing others and shifting right.
uint32_t get_t(const uint32_t instr) { return (instr & T_BITS) >> 16; }

// Gets the s bits, clearing others and shifting right.
uint32_t get_s(const uint32_t instr) { return (instr & S_BITS) >> 21; }

// $d = $s + $t.
void mips_add(const uint32_t instr, uint32_t registers[32]) {
    int d = (int16_t)get_d(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[d] = registers[s] + registers[t];
}

// $d = $s - $t.
void mips_sub(const uint32_t instr, uint32_t registers[32]) {
    int d = (int16_t)get_d(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[d] = registers[s] - registers[t];
}
// $d = $s & $t.
void mips_and(const uint32_t instr, uint32_t registers[32]) {
    int d = (int16_t)get_d(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[d] = registers[s] & registers[t];
}

// $d = $s | $t.
void mips_or(const uint32_t instr, uint32_t registers[32]) {
    int d = (int16_t)get_d(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[d] = registers[s] | registers[t];
}

// $d = ($s < $t).
void mips_slt(const uint32_t instr, uint32_t registers[32]) {
    int d = (int16_t)get_d(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[d] = registers[s] < registers[t];
}

// $d = $s * $t.
void mips_mul(const uint32_t instr, uint32_t registers[32]) {
    int d = (int16_t)get_d(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[d] = registers[s] * registers[t];
}

// If ($s == $t) PC += i.
void mips_beq(FILE *const fptr, const uint32_t instr, uint32_t registers[32]) {
    int i = (int16_t)get_i(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    if (registers[s] != registers[t]) {
        return;
    }
    if (i >= 0) {
        for (int j = 0; j <= i; ++j) {
            get_next_instruction(fptr);
        }
    } else {
        for (int j = 0; j <= -1 * i; ++j) {
            goto_previous_instruction(fptr);
        }
    }
}

// If ($s != $t) PC += i.
void mips_bne(FILE *const fptr, const uint32_t instr, uint32_t registers[32]) {
    int i = (int16_t)get_i(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    if (registers[s] == registers[t]) {
        return;
    }
    if (i >= 0) {
        for (int j = 0; j <= i; ++j) {
            get_next_instruction(fptr);
        }
    } else {
        for (int j = 0; j <= -1 * i; ++j) {
            goto_previous_instruction(fptr);
        }
    }
}

// $t = $s + i.
void mips_addi(const uint32_t instr, uint32_t registers[32]) {
    int i = (int16_t)get_i(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[t] = registers[s] + (uint32_t)i;
}

// $t = $s < i.
void mips_slti(const uint32_t instr, uint32_t registers[32]) {
    int i = (int16_t)get_i(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[t] = registers[s] < (uint32_t)i;
}

// $t = $s & i.
void mips_andi(const uint32_t instr, uint32_t registers[32]) {
    int i = (int16_t)get_i(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[t] = registers[s] & (uint32_t)i;
}

// $t = $s | i.
void mips_ori(const uint32_t instr, uint32_t registers[32]) {
    int i = (int16_t)get_i(instr);
    int t = (int16_t)get_t(instr);
    int s = (int16_t)get_s(instr);
    registers[t] = registers[s] | (uint32_t)i;
}

// $t = i << 16u.
void mips_lui(const uint32_t instr, uint32_t registers[32]) {
    int i = (int16_t)get_i(instr);
    int t = (int16_t)get_t(instr);
    registers[t] = (uint32_t)i << 16u;
}

// Syscall function which returns non-zero if execution should stop.
int mips_syscall(uint32_t registers[32]) {
    uint32_t v0 = registers[2];
    uint32_t a0 = registers[4];
    switch (v0) {
    case 1:
        printf("%u", a0);
        break;
    case 11:
        printf("%c", a0 & 0xFFu);
        break;
    case 10:
        return 1;
    default:
        printf("Unknown system call: %d\n", v0);
        return 1;
    }
    return 0;
}