RosettaCodeData/Task/N-queens-problem/BCPL/n-queens-problem-2.bcpl

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GET "libhdr.h"
GET "mc.h"
MANIFEST {
lo=1; hi=16
dlevel=#b0000
// Register mnemonics
ld = mc_a
row = mc_b
rd = mc_c
poss = mc_d
p = mc_e
count = mc_f
}
LET start() = VALOF
{ // Load the dynamic code generation package
LET mcseg = globin(loadseg("mci386"))
LET mcb = 0
UNLESS mcseg DO
{ writef("Trouble with MC package: mci386*n")
GOTO fin
}
// Create an MC instance for hi functions with a data space
// of 10 words and code space of 40000
mcb := mcInit(hi, 10, 40000)
UNLESS mcb DO
{ writef("Unable to create an mci386 instance*n")
GOTO fin
}
mc := 0 // Currently no selected MC instance
mcSelect(mcb)
mcK(mc_debug, dlevel) // Set the debugging level
FOR n = lo TO hi DO
{ mcComment("*n*n// Code for a %nx%n board*n", n, n)
gencode(n) // Compile the code for an nxn board
}
mcF(mc_end) // End of code generation
writef("Code generation complete*n")
FOR n = lo TO hi DO
{ LET k = mcCall(n)
writef("Number of solutions to %i2-queens is %i9*n", n, k)
}
fin:
IF mc DO mcClose()
IF mcseg DO unloadseg(mcseg)
writef("*n*nEnd of run*n")
}
AND gencode(n) BE
{ LET all = (1<<n) - 1
mcKKK(mc_entry, n, 3, 0)
mcRK(mc_mv, ld, 0)
mcRK(mc_mv, row, 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 | row | rd)) & all
mcRR(mc_or, poss, row)
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, row)
mcR (mc_push, rd)
mcR (mc_push, poss)
// Call try((ld+p)<<1, row+p, (rd+p)>>1)
mcRR(mc_add, ld, p)
mcRK(mc_lsh, ld, 1) // ld := (ld+p)<<1
mcRR(mc_add, row, p) // row := row+p
mcRR(mc_add, rd, p)
mcRK(mc_rsh, rd, 1) // rd := (rd+p)>>1
cmpltry(i+1, n, all) // Compile code for row i+1
mcR (mc_pop, poss) // Restore the state
mcR (mc_pop, rd)
mcR (mc_pop, row)
mcR (mc_pop, ld)
mcRK(mc_cmp, poss, 0)
mcJL(mc_jne, M) // } REPEATWHILE poss
}
mcL(mc_lab, L)
mcComment("// End of code from try(%n, %n, %n)*n*n",
i, n, all)
}