/* capsule.c -- a capsule of F18 code.  See capsule.h.
 *
 * Nothing here uses the C library.
 */
#include "v4/capsule.h"
#include "v4/iword.h"
#include "v4/opcode.h"

/* A stretch of zeros shorter than this, between words that are not zero, is
 * sent with them: starting a new stretch costs four words. */
#define GAP 4u

static v4_cell words_of(unsigned a, unsigned b, unsigned c, unsigned d)
{
    unsigned op[V4_SLOT_COUNT];
    unsigned k;
    op[0] = a; op[1] = b; op[2] = c; op[3] = d;
    for (k = 4; k < V4_SLOT_COUNT; k++) op[k] = V4_OP_NOP;
    return (v4_cell)v4_iword_assemble(op, 0);
}

/* `jump addr`, the jump in the first slot so that its address is as wide as
 * an address can be */
static v4_cell jump_to(v4_cell addr)
{
    v4_ucell mask = (v4_ucell)v4_iword_slot_mask(0);
    v4_ucell word = (v4_ucell)words_of(V4_OP_JUMP, V4_OP_NOP, V4_OP_NOP, V4_OP_NOP);
    return (v4_cell)((word & ~mask) | ((v4_ucell)addr & mask));
}

unsigned v4_capsule_write(const v4_node *n, v4_cell start,
                          void (*out)(void *self, v4_cell word), void *self)
{
    unsigned k = 0, written = 0;

    while (k < V4_NODE_WORDS) {
        unsigned first, last, zeros, i;

        if (n->mem[k] == 0) { k++; continue; }
        first = last = k;
        zeros = 0;
        for (i = k + 1; i < V4_NODE_WORDS && zeros < GAP; i++) {
            if (n->mem[i] != 0) { last = i; zeros = 0; } else zeros++;
        }
        out(self, words_of(V4_OP_FETCH_P, V4_OP_BANG_A, V4_OP_FETCH_P, V4_OP_PUSH));
        out(self, (v4_cell)first);
        out(self, (v4_cell)(last - first));
        out(self, words_of(V4_OP_FETCH_P, V4_OP_STORE_INC, V4_OP_UNEXT, V4_OP_NOP));
        for (i = first; i <= last; i++) out(self, n->mem[i]);
        written += 4u + (last - first + 1u);
        k = last + 1;
    }
    out(self, jump_to(start));
    return written + 1u;
}