// The OS/K Team licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#include <pc/arch.h>

//
// Read the "DECD" file before reading this code
//

static void check_param_type(ctx_t *ctx, instr_t *in,
                             uint prm, uchar fmt, int which)
{
    bool ok;

    if (prm == P_REG)
        ok = (fmt == A_REG);

    else if (prm == P_IMM)
        ok = (fmt == A_IMM64);

    else /* if (prm == P_MEM) */
        ok = ACC_FMT_IS_MEM(fmt);

    if (!ok)
        _except(ctx, E_ILL,
            "FT%d not matching %s's expected parameter types: "
            "fmt=0x%x prm=0x%x", which, in->full, fmt, prm);
}

//
// Verify that access to a certain register is legal
//
static void checkreg(ctx_t *ctx, uint reg, bool inv_is_ok)
{
    if (reg >= NREGS)
        _except(ctx, E_ILL, "Inexistent register: %u", reg);

    if (reg == INV)
    {
        if (!inv_is_ok)
            _except(ctx, E_ILL, "INV dereference");
        else
            return;
    }

    if (ctx->r[reg].flags & (RES | CTL))
        //_except(ctx, E_ACC, "Reserved REG: %u", reg);

    if (ctx->r[reg].flags & SYS)
        if (cr0 & UF)
            _except(ctx, E_SYS, "User access to SYS REG: %u", reg);
}

//
// Extract operand according to fmt
//
void extract_param(ctx_t *ctx, acc_t *p, uchar fmt)
{
    uint mlen, mfmt;
    ushort temp;

    p->type = fmt;

    if (fmt == A_REG)
    {
        p->reg = ctx->get(ctx);
        checkreg(ctx, p->reg, 0);

        p->val = R(p->reg);
        
        return;
    }

    else if (fmt == A_IMM64)
    {
        p->val = ctx->get(ctx);
        p->val |= (ulong)ctx->get(ctx) << 16;
        p->val |= (ulong)ctx->get(ctx) << 32;
        p->val |= (ulong)ctx->get(ctx) << 48;
        
        return;
    }

    assert(ACC_FMT_IS_MEM(fmt));

    //
    // Handle a memory access
    //

    mlen = fmt & AM_MLEN_MASK;
    mfmt = fmt & AM_MFMT_MASK;

    p->mlen = (mlen == AM_8ACC ? 1
            : (mlen == AM_16ACC ? 2
            : (mlen == AM_32ACC ? 4
            : (mlen == AM_64ACC ? 8 : 0))));

    if (p->mlen == 0)
        _except(ctx, E_ILL, "Invalid MLEN for access: %x", fmt);
    
    switch (mfmt)
    {
        case AM_IMM64:
            p->addr = ctx->get(ctx);
            p->addr |= (ulong)ctx->get(ctx) << 16;
            p->addr |= (ulong)ctx->get(ctx) << 32;
            p->addr |= (ulong)ctx->get(ctx) << 48;
            break;
        
        case AM_RR:
        case AM_RRI:
        case AM_RRII:
            temp = ctx->get(ctx);
            p->reg1 = temp >> 8;
            p->reg2 = temp & 0xFF;
            
            checkreg(ctx, p->reg1, 1);
            checkreg(ctx, p->reg2, 1);
            
            if (mfmt == AM_RRI)
            {
                p->imm1 = 1;
                p->imm2 = ctx->get(ctx);
            }
            
            else if (mfmt == AM_RRII)
            {
                p->imm1 = ctx->get(ctx);
                p->imm2 = ctx->get(ctx);
            }
            
            else
            {
                p->imm1 = 1;
                p->imm2 = 0;
            }

            p->addr = R(p->reg1) + R(p->reg2)
                        * (long)(short)p->imm1
                        + (long)(short)p->imm2;
            
            break;
            
        default:
            _except(ctx, E_ILL, "Invalid MFMT for access: %x", fmt);
    }
}

void decode(ctx_t *ctx)
{
    instr_t *in;

    acc_t p1 = { 0 };
    acc_t p2 = { 0 };
    acc_t p3 = { 0 };

    bool rep = 0;
    bool lock, nomore;

    ushort w1, w2;
    uchar f1 = 0, f2 = 0, f3 = 0;

    rpc = rip;

    //
    // Process the first word of the instruction
    //
    w1 = ctx->get(ctx);

    // Extract first word flags

    lock = !!(w1 & SUFF_LOCK);
    nomore = !!(w1 & SUFF_NOMORE);

    if (w1 & SUFF_COND)
        ctx->cond = ctx->get(ctx);
    else
        ctx->cond = 0;

    w1 &= ~(SUFF_LOCK|SUFF_NOMORE|SUFF_COND);

    // Find instruction

    if (w1 >= NINSTRS)
    {
        _except(ctx, E_ILL, "No such INSTR: 0x%hX", w1);
    }

    in = &ctx->i[w1];
    ctx->cur_in = in;

    if (!nomore)
    {
        //
        // Process second word
        //

        w2 = ctx->get(ctx);

        // REP and COND
        rep = !!(w2 & SUFF_REP);

        // Fn
        f3 = (w2 >> F3_SHIFT) & Fx_MASK;
        f2 = (w2 >> F2_SHIFT) & Fx_MASK;
        f1 = w2 & Fx_MASK;
    }

    //
    // Deal with operand 1
    //

    if (in->prm1 == NOPRM)
    {
        if (f1 || f2 || f3)
        {
            _except(ctx, E_ILL,
                "FTn (%u,%u,%u) filled for 0-param INSTR '%s'",
                    f1, f2, f3, in->full);
        }

        exec_instr(ctx, in, NULL, NULL, NULL, lock, rep);
        return;
    }

    check_param_type(ctx, in, in->prm1, f1, 1);
    extract_param(ctx, &p1, f1);

    //
    // Deal with operand 2
    //

    if (in->prm2 == NOPRM)
    {
        if (f2 || f3)
        {
            _except(ctx, E_ILL,
                "FT3/FT2 (%u,%u,%u) filled for 1-param INSTR '%s'",
                    f1, f2, f3, in->full);
        }

        exec_instr(ctx, in, &p1, NULL, NULL, lock, rep);
        return;
    }

    check_param_type(ctx, in, in->prm2, f2, 2);
    extract_param(ctx, &p2, f2);

    //
    // Deal with operand 3
    //

    if (in->prm3 == NOPRM)
    {
        if (f3)
        {
            _except(ctx, E_ILL,
                "FT3 (%u,%u,%u) filled for 2-param INSTR '%s'",
                    f1, f2, f3, in->full);
        }

        exec_instr(ctx, in, &p1, &p2, NULL, lock, rep);
        return;
    }

    check_param_type(ctx, in, in->prm3, f3, 3);
    extract_param(ctx, &p3, f3);

    exec_instr(ctx, in, &p1, &p2, &p3, lock, rep);
}