User guide

202 CHAPTER 11. THE MC PACKAGE
}
AND gencode(n) BE
{ LET all = (1<<n) - 1
mcKKK(mc_entry, n, 3, 0)
mcRK(mc_mv, ld, 0)
mcRK(mc_mv, col, 0)
mcRK(mc_mv, rd, 0)
mcRK(mc_mv, count, 0)
cmpltry(1, n, all) // Compile the outermost call of try
mcRR(mc_mv, mc_a, count) // return count
mcF(mc_rtn)
mcF(mc_endfn)
}
AND cmpltry(i, n, all) BE
{ LET L = mcNextlab()
mcComment("*n// Start of code from try(%n, %n, %n)*n", i, n, all)
mcRR(mc_mv, poss, ld) // LET poss = (~(ld | col | rd)) & all
mcRR(mc_or, poss, col)
mcRR(mc_or, poss, rd)
mcR (mc_not, poss)
mcRK(mc_and, poss, all)
mcRK(mc_cmp, poss, 0) // IF poss DO
TEST n-i<=2
THEN mcJS(mc_jeq, L) // (use a short jump if near the last row)
ELSE mcJL(mc_jeq, L)
TEST i=n
THEN { // We can place a queen in the final row.
mcR(mc_inc, count) // count := count+1
}
ELSE { // We can place queen(s) in a non final row.
LET M = mcNextlab()
mcL (mc_lab, M) // { Start of REPEATWHILE loop
mcRR(mc_mv, p, poss) // LET p = poss & -poss
mcR (mc_neg, p)
mcRR(mc_and, p, poss) // // p is a valid queens position
mcRR(mc_sub, poss, p) // poss := poss - p
mcR (mc_push, ld) // Save current state
mcR (mc_push, col)
mcR (mc_push, rd)
mcR (mc_push, poss)
// Call try((ld+p)<<1, col+p, (rd+p)>>1)
mcRR(mc_add, ld, p)
mcRK(mc_lsh, ld, 1) // ld := (ld+p)<<1