kvisc/vm/pc/exec.c

// 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>

#define rfx R(RFX)

bool eval_cond(uint cond)
{
    bool neg = cond & (1 << 4);
    bool ok;
    
    cond &= ~(1 << 4);
    
    switch (cond)
    {
        case CD_NONE: ok = 1;   break;

        case CD_C: ok = rfx&CF; break;
        case CD_O: ok = rfx&OF; break;
        case CD_Z: ok = rfx&ZF; break;
        case CD_S: ok = rfx&SF; break;
        case CD_P: ok = rfx&PF; break;

        case CD_BE: ok = rfx&CF || rfx&ZF;                      break;
        case CD_L:  ok = !(rfx&SF) != !(rfx&OF);                break;
        case CD_LE: ok = rfx&ZF || (!(rfx&SF) != !(rfx&OF));    break;

        case CD_AXZ: ok = !R(RAX); break;
        case CD_BXZ: ok = !R(RBX); break;
        case CD_CXZ: ok = !R(RCX); break;
        case CD_DXZ: ok = !R(RDX); break;

        default:
            _except(E_ILL, "Invalid COND value: 0x%x", (neg?cond|(1<<4):cond));
    }
    
    return neg ? !ok : !!ok;
}

#define OUTPUT(p, r) {                                                      \
    if (p->type == A_REG)                                                   \
        R(p->reg) = r;                                                      \
    else if (ACC_IS_MEM(p))                                                 \
        writemem(r, p->addr, p->mlen);                                      \
    else _except(E_ACC, "Trying to output to an IMM");                      \
    }

//
// Executes an instruction
//
void exec_instr(instr_t *in,
                acc_t *p1,
                acc_t *p2, 
                acc_t *p3, 
                bool lock,
                bool rep)
{
    uint out;
    ulong r1 = 0, r2 = 0, r3 = 0;

    // Global instruction counter
    ctx->ninstrs++;

    //
    // For REPs we evaluate the condition AFTER running the instruction,
    // in a do ... while(cond) fashion
    //
    if (ctx->cond && in->func != i_b)     // 'B' instruction is special
        if (!rep && !eval_cond(ctx->cond))
            return;

    if (ctx->dumpsw)
        dump_instr(in, p1, p2, p3, lock, rep);

do_rep:
    out = in->func(p1, p2, p3, &r1, &r2, &r3);

    if (out)
    {
        OUTPUT(p1, r1);
        if (out >= 2) OUTPUT(p2, r2);
        if (out >= 3) OUTPUT(p3, r3);
        R(RZX) = 0;
    }

    if (rep)
    {
        // RCX remains untouched when condition fails
        if (!eval_cond(ctx->cond))
            return;

        if (R(RCX) > 0)
            R(RCX)--;

        if (R(RCX) == 0)
            return;

        // Should we really count REP's in instruction count?
        ctx->ninstrs++;
#if 0
        // Show that we're REP'ing
        if (ctx->dumpsw)
            dump_instr(in, p1, p2, p3, lock, rep);
#endif

        goto do_rep;
    }
}