--- /dev/null
+/*
+
+Copyright © 2018-2019 Simon Forman
+
+This file is part of Thun
+
+Thun is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+Thun is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with Thun. If not see <http://www.gnu.org/licenses/>.
+
+The Joy interpreter that this implements is pretty crude. the only types
+are 16-bit integers and linked lists. The lists are 32-bit words divided
+into two 16-bit fields. The high half is the node value and the low half
+points directly (not offset) to the next cell, zero terminates the list.
+
+The expression is expected to be already written in RAM as a linked list at
+the time the mainloop starts. As yet there is no support for actually doing
+this. Both the new stack and expression cells are written to the same heap
+intermixed. The stack and expression pointers never decrease, the whole
+history of the computation is recorded in RAM. If the computation of the
+expression overruns the end of RAM (or 16-bits whichever comes first) the
+machine crashes.
+
+At the moment, functions are recognized by setting high bit, but I don't
+think I remembered to set the bits during compilation, so it won't work
+at all right now. Er... Boo. Anyhow, the whole thing is very crude and
+not at all what I am hoping eventually to build.
+
+But it's a start, and I feel good about emitting machine code (even if the
+program doesn't do anything useful yet.)
+
+*/
+:- use_module(library(assoc)).
+:- use_module(library(clpfd)).
+
+
+do :- Program = [
+ ヲ,∅,⟴,ヵ,メ,ョ,
+ [グ,ケ,ゲ,ド,ゴ,サ],ヮ(cons),
+ [ザ,シ],ヮ(dup),
+ [グ,ス,[],[ジ,ス,[ズ,セ,ス,[ゼ,ソ],[タ,ゾ],ヰ,ヂ],ヱ],ヰ,チ],ヮ(i),
+ [ヶ,ペ],ワ(new),
+ [ナ,ズ,セ,ネ,ヒ,ド,ャ,ペ],ワ(swap),
+ [new,cons],≡(unit),
+ [dup,i],≡(x),
+ [swap,cons],≡(swons)
+ ],
+compile_program(Program, Binary),
+write_binary('joy_asm.bin', Binary).
+
+
+compile_program(Program, Binary) :-
+ phrase((init, ⦾(Program, IR)), [], [Context]),
+ phrase(⟐(IR), ASM),
+ phrase(linker(ASM), EnumeratedASM),
+ foo(Context),
+ phrase(asm(EnumeratedASM), Binary).
+
+foo(Context) :-
+ get_assoc(dictionary, Context, D),
+ assoc_to_list(D, Dictionary),
+ portray_clause(Dictionary).
+
+
+/*
+
+This first stage ⦾//2 converts the Joy description into a kind of intermediate
+representation that models the Joy interpreter on top of the machine but doesn't
+actually use assembly instructions. It also manages the named registers and
+memory locations so thet don't appear in the program.
+
+The idea here is to extract the low-level "primitives" needed to define the Joy
+interpreter to make it easier to think about (and maybe eventually retarget other
+CPUs.)
+
+ */
+
+⦾([], []) --> [].
+
+⦾([ヲ|Terms], Ts) --> % Preamble.
+ % Initialize context/state/symbol table.
+ set(dict_ptr, 11), % Reg 11 is a pointer used during func lookup.
+ set(dict_top, 12), % Reg 12 points to top of dictionary.
+ set(dict, 0), % Address of top of dict during compilation.
+ set(done, _DONE), % DONE label (logic variable.)
+ set(expr, 4), % Reg 4 points to expression.
+ set(halt, _HALT), % HALT label (logic variable.)
+ set(main, _MAIN), % MAIN label (logic variable.)
+ set(reset, _Reset), % Reset label (logic variable.)
+ set(sp, 2), % Reg 2 points to just under top of stack.
+ set(temp0, 6), % Reg 6 is a temp var.
+ set(temp1, 7), % Reg 7 is a temp var.
+ set(temp2, 8), % Reg 8 is a temp var.
+ set(temp3, 9), % Reg 9 is a temp var.
+ set(term, 5), % Reg 4 holds current term.
+ set(tos, 3), % Reg 3 holds Top of Stack.
+ ⦾(Terms, Ts).
+
+⦾([ヵ|Terms], [ % Initialization.
+ jump(Over), % Oberon bootloader writes MemLim to RAM[12] and
+ asm(allocate(_, 16)), % stackOrg to RAM[24], we don't need these
+ label(Over), % but they must not be allowed to corrupt our code.
+ set_reg_const(0, 0), % zero out the root cell.
+ write_ram(0, 0),
+ set_reg_const(SP, 0x1000),
+ set_reg_const(EXPR, 0x500),
+ set_reg_label(DICT_TOP, LastWord),
+ set_reg_const(TOS, 0),
+ set_reg_const(TERM, 0),
+ asm(store_word(TOS, SP, 0)) % RAM[SP] := 0
+ |Ts]) -->
+ get([dict_top, DICT_TOP, expr, EXPR, sp, SP, term, TERM, tos, TOS]),
+ ⦾(Terms, Ts), get(dict, LastWord).
+
+⦾([メ|Terms], [ % Mainloop.
+ label(MAIN),
+ if_zero(EXPR, HALT),
+ deref(EXPR),
+ split_word(TERM, EXPR),
+ if_literal(TERM, PUSH),
+ lookup(DICT_PTR, DICT_TOP, TERM, HALT), % Jump to command or if not found halt.
+ label(PUSH), push(TOS, TERM, SP), % stack = TERM, stack
+ label(DONE), write_ram(SP, TOS), % RAM[SP] := TOS
+ jump(MAIN)
+ |Ts]) -->
+ get([dict_ptr, DICT_PTR, dict_top, DICT_TOP, done, DONE, expr, EXPR,
+ halt, HALT, main, MAIN, sp, SP, term, TERM, tos, TOS]),
+ ⦾(Terms, Ts).
+
+⦾([Body, ≡(NameAtom)|Terms], [defi(Name, B, Prev, I, SP, TOS)|Ts]) -->
+ get(dict, Prev), set(dict, Name), get([sp, SP, tos, TOS]),
+ inscribe(NameAtom, Name), ⦾(Terms, Ts), lookup(i, I), lookup(Body, B).
+
+⦾([Body, ヮ(NameAtom)|Terms], [definition(Name, DONE, B, Prev)|Ts]) -->
+ get(dict, Prev), set(dict, Name), inscribe(NameAtom, Name),
+ get(done, DONE), ⦾([Body, Terms], [B, Ts]).
+
+⦾([Body, ワ(NameAtom)|Terms], [definition(Name, MAIN, B, Prev)|Ts]) -->
+ get(dict, Prev), set(dict, Name), inscribe(NameAtom, Name),
+ get(main, MAIN), ⦾([Body, Terms], [B, Ts]).
+
+⦾([P, T, E, ヰ|Terms], [br(Predicate, Then, Else)|Ts]) -->
+ ⦾([P, T, E, Terms], [Predicate, Then, Else, Ts]).
+
+⦾([P, B, ヱ|Terms], [repeat_until(Predicate, Body)|Ts]) -->
+ ⦾([P, B, Terms], [Predicate, Body, Ts]).
+
+⦾([Term|Terms], [T|Ts]) --> ⦾(Term, T), ⦾(Terms, Ts).
+
+⦾(∅, dw(0)) --> [].
+⦾(⟴, label(Reset)) --> get(reset, Reset).
+⦾(ョ, halt(HALT)) --> get(halt, HALT).
+⦾(グ, pop(TEMP0, TOS)) --> get(temp0, TEMP0), get(tos, TOS).
+⦾(シ, push(TOS, TOS, SP)) --> get(tos, TOS), get(sp, SP).
+⦾(ケ, high_half(TEMP1, TOS)) --> get(temp1, TEMP1), get(tos, TOS).
+⦾(サ, merge(SP, TOS)) --> get(tos, TOS), get(sp, SP).
+⦾(ザ, swap_halves(TOS)) --> get(tos, TOS).
+⦾(ズ, deref(TEMP0)) --> get(temp0, TEMP0).
+⦾(ス, if_zero(TEMP0)) --> get(temp0, TEMP0).
+⦾(ソ, asm(mov(EXPR, TEMP3))) --> get(expr, EXPR), get(temp3, TEMP3).
+⦾(ャ, asm(ior(TOS, TEMP1, SP))) --> get(tos, TOS), get(temp1, TEMP1), get(sp, SP).
+⦾(タ, add_const(TEMP2, SP, 8)) --> get(temp2, TEMP2), get(sp, SP).
+⦾(ジ, add_const(TEMP3, SP, 4)) --> get(temp3, TEMP3), get(sp, SP).
+⦾(チ, add_const(SP, SP, 4)) --> get(sp, SP).
+⦾(セ, chop_word(TEMP1, TEMP0)) --> get(temp0, TEMP0), get(temp1, TEMP1).
+⦾(ト, chop_word(TEMP0, TOS)) --> get(temp0, TEMP0), get(tos, TOS).
+⦾(ネ, chop_word(TEMP2, TOS)) --> get(temp2, TEMP2), get(tos, TOS).
+⦾(ゼ, or_inplace(TEMP1, EXPR)) --> get(expr, EXPR), get(temp1, TEMP1).
+⦾(ゲ, or_inplace(TEMP0, TEMP1)) --> get(temp0, TEMP0), get(temp1, TEMP1).
+⦾(ヒ, or_inplace(TEMP0, TEMP2)) --> get(temp0, TEMP0), get(temp2, TEMP2).
+⦾(ゾ, or_inplace(TEMP1, TEMP2)) --> get(temp1, TEMP1), get(temp2, TEMP2).
+⦾(ド, write_cell(TEMP0, SP)) --> get(temp0, TEMP0), get(sp, SP).
+⦾(ヂ, write_cell(TEMP1, SP)) --> get(temp1, TEMP1), get(sp, SP).
+⦾(ペ, write_cell(TOS, SP)) --> get(tos, TOS), get(sp, SP).
+⦾(ゴ, low_half(TOS)) --> get(tos, TOS).
+⦾(ナ, low_half(TEMP0, TOS)) --> get(temp0, TEMP0), get(tos, TOS).
+⦾(ヶ, low_half(TOS, SP)) --> get(sp, SP), get(tos, TOS).
+
+
+/*
+
+Context (state) manipulation for the ⦾//2 relation.
+
+Association lists are used to keep a kind of symbol table as well as a dictionary
+of name atoms to address logic variables for defined Joy functions.
+
+*/
+
+init, [Context] -->
+ {empty_assoc(C), empty_assoc(Dictionary),
+ put_assoc(dictionary, C, Dictionary, Context)}.
+
+get([]) --> !.
+get([Key, Value|Ts]) --> !, get(Key, Value), get(Ts).
+
+get(Key, Value) --> state(Context), {get_assoc(Key, Context, Value)}.
+set(Key, Value) --> state(ContextIn, ContextOut),
+ {put_assoc(Key, ContextIn, Value, ContextOut)}.
+
+inscribe(NameAtom, Label) --> state(ContextIn, ContextOut),
+ {get_assoc(dictionary, ContextIn, Din),
+ put_assoc(NameAtom, Din, Label, Dout),
+ put_assoc(dictionary, ContextIn, Dout, ContextOut)}.
+
+lookup([], []) --> !.
+lookup([T|Ts], [V|Vs]) --> !, lookup(T, V), lookup(Ts, Vs).
+lookup(NameAtom, Label) --> state(Context),
+ {get_assoc(dictionary, Context, D), get_assoc(NameAtom, D, Label)}.
+
+state(S), [S] --> [S].
+state(S0, S), [S] --> [S0].
+
+
+/*
+
+This second stage ⟐//1 converts the intermediate representation to assembly
+language.
+
+*/
+
+⟐([]) --> [].
+⟐([Term|Terms]) --> ⟐(Term), ⟐(Terms).
+
+⟐(if_literal(Reg, Label)) --> % commands marked by setting high bit.
+ [and_imm(0, Reg, 0x8000), % 1 << 15
+ eq_offset(Label)].
+
+% if reg = 0 jump to label.
+⟐(if_zero(Reg, Label)) --> [sub_imm(Reg, Reg, 0), eq_offset(Label)].
+
+⟐(set_reg_const(Reg, Immediate)) --> {Immediate >= -(2^15), Immediate < 2^16}, !,
+ [mov_imm(Reg, Immediate)].
+
+⟐(set_reg_const(Reg, Immediate)) --> {Immediate >= 0, Immediate < 2^33}, !, % FIXME: handle negative numbers.
+ {high_half_word(Immediate, HighHalf), low_half_word(Immediate, LowHalf)},
+ [ mov_imm_with_shift(Reg, HighHalf), ior_imm(Reg, Reg, LowHalf)].
+
+⟐(set_reg_label(Reg, Label)) --> [mov_imm(Reg, Label)].
+
+⟐( noop) --> [mov(0, 0)].
+⟐( halt(Halt)) --> [label(Halt), do_offset(Halt)].
+⟐( asm(ASM)) --> [ASM].
+⟐(label(Label)) --> [label(Label)].
+⟐( jump(Label)) --> [do_offset(Label)].
+⟐( dw(Int)) --> [word(Int)].
+
+⟐( low_half(Reg)) --> [and_imm(Reg, Reg, 0xffff)].
+⟐( low_half(To, From)) --> [and_imm(To, From, 0xffff)].
+⟐( high_half(Reg)) --> [mov_imm_with_shift(0, 0xffff), and(Reg, Reg, 0)].
+⟐(high_half(To, From)) --> [mov_imm_with_shift(0, 0xffff), and(To, From, 0)].
+
+⟐(swap_halves(Register)) --> [ror_imm(Register, Register, 16)].
+⟐(swap_halves(To, From)) --> [ror_imm( To, From, 16)].
+
+⟐(high_half_to(To, From)) --> ⟐([swap_halves(To, From), low_half(To)]).
+
+⟐(split_word(To, From)) --> ⟐([high_half_to(To, From), low_half(From)]).
+
+⟐(chop_word(To, From)) --> ⟐([high_half(To, From), low_half(From)]).
+
+⟐(merge(SP, TOS)) -->
+ [lsl_imm(0, SP, 16),
+ ior(TOS, TOS, 0),
+ add_imm(SP, SP, 4)].
+
+⟐(push(TOS, TERM, SP)) -->
+ [lsl_imm(TOS, TERM, 16), % TOS := TERM << 16
+ ior(TOS, TOS, SP), % TOS := TOS | SP
+ add_imm(SP, SP, 4)]. % SP += 1 (word, not byte)
+
+⟐( write_ram(To, From)) --> [store_word(From, To, 0)].
+⟐(write_cell(From, SP)) --> [add_imm(SP, SP, 4), store_word(From, SP, 0)].
+
+⟐(deref(Reg)) --> [load_word(Reg, Reg, 0)].
+
+⟐(or_inplace(To, From)) --> [ior(To, To, From)].
+
+⟐(definition(Label, Exit, Body, Prev)) -->
+ ⟐([
+ dw(Prev),
+ label(Label),
+ Body,
+ jump(Exit)
+ ]).
+
+⟐(defi(Label, Body, Prev, I, SP, TOS)) -->
+ ⟐([dw(Prev),
+ label(Label),
+ defi_def(BodyLabel, SP, TOS),
+ jump(I)]),
+ dexpr(Body, BodyLabel).
+
+⟐(defi_def(Label, SP, TOS)) -->
+ [mov_imm_with_shift(TOS, Label),
+ ior(TOS, TOS, SP)],
+ ⟐(write_cell(TOS, SP)).
+
+⟐(lookup(PTR, TOP, TERM, Exit)) -->
+ [mov(PTR, TOP), % point to the top of the dictionary.
+ label(Lookup),
+ sub(0, TERM, PTR), eq(PTR), % if the term is found jump to it,
+ sub_imm(PTR, PTR, 4), % else load the next pointer.
+ load_word(PTR, PTR, 0),
+ sub_imm(PTR, PTR, 0), eq_offset(Exit), % exit if it's zero.
+ do_offset(Lookup)]. % loop to the top.
+
+⟐(repeat_until(Condition, Body)) -->
+ {add_label(Condition, End, ConditionL)},
+ ⟐([
+ label(Loop),
+ Body,
+ ConditionL,
+ jump(Loop),
+ label(End)
+ ]).
+
+⟐(br(Condition, [], Else)) --> !,
+ {add_label(Condition, END, ConditionL)},
+ ⟐([ConditionL, Else, label(END)]).
+
+⟐(br(Condition, Then, Else)) -->
+ {add_label(Condition, THEN, ConditionL)},
+ ⟐([
+ ConditionL, Else, jump(END),
+ label(THEN), Then, label(END)
+ ]).
+
+⟐(add_const(To, From, Immediate)) --> [add_imm(To, From, Immediate)].
+
+⟐(pop(Reg, TOS)) --> ⟐([split_word(Reg, TOS), deref(TOS)]).
+
+
+/*
+
+Support for ⟐//1 second stage.
+
+The dexpr//2 DCG establishes a sequence of labeled expr_cell/2 pseudo-assembly
+memory locations as a linked list that encodes a Prolog list of Joy function
+labels comprising e.g. the body of some Joy definition.
+
+*/
+
+dexpr([], 0) --> [].
+dexpr([Func|Rest], ThisCell) -->
+ [label(ThisCell), expr_cell(Func, NextCell)],
+ dexpr(Rest, NextCell).
+
+/*
+
+The add_label/3 relation is a meta-logical construct that accepts a comparision
+predicate (e.g. if_zero/2) and "patches" it by adding the Label logic variable
+to the end.
+
+*/
+
+add_label(CmpIn, Label, CmpOut) :-
+ CmpIn =.. F,
+ append(F, [Label], G),
+ CmpOut =.. G.
+
+/*
+
+Two simple masking predicates.
+
+*/
+
+high_half_word(I, HighHalf) :- HighHalf is I >> 16 /\ 0xFFFF.
+low_half_word( I, LowHalf) :- LowHalf is I /\ 0xFFFF.
+
+
+/*
+
+Linker
+
+*/
+
+linker(ASM) --> enumerate_asm(ASM, 0, _).
+
+enumerate_asm( [], N, N) --> !, [].
+enumerate_asm( [Term|Terms], N, M) --> !, enumerate_asm(Term, N, O), enumerate_asm(Terms, O, M).
+enumerate_asm( label(N) , N, N) --> !, [].
+enumerate_asm(allocate(N, Bytes), N, M) --> !, {Bits is 8 * Bytes}, [skip(Bits)], {align(N, Bytes, M)}.
+enumerate_asm( Instr, N, M) --> [(Z, Instr)], {align(N, 0, Z), align(Z, 4, M)}.
+
+align(_, Bytes, _) :- (Bytes < 0 -> write('Align negative number? No!')), !, fail.
+align(N, 1, M) :- !, M is N + 1.
+align(N, Bytes, M) :- N mod 4 =:= 0, !, M is N + Bytes.
+align(N, Bytes, M) :- Padding is 4 - (N mod 4), M is N + Bytes + Padding.
+
+
+/*
+
+Assembler
+
+*/
+
+asm([]) --> !, [].
+asm([ skip(Bits)|Rest]) --> !, skip(Bits), asm(Rest).
+asm([(N, Instruction)|Rest]) --> !, asm(N, Instruction), asm(Rest).
+
+asm(_, expr_cell(Func, NextCell)) --> !,
+ {Data is (Func << 16) \/ NextCell}, asm(_, word(Data)).
+
+asm(_, word(Word)) --> !, {binary_number(Bits, Word)}, collect(32, Bits).
+
+asm(_, load_word(A, B, Offset)) --> !, instruction_format_F2(0, 0, A, B, Offset).
+asm(_, load_byte(A, B, Offset)) --> !, instruction_format_F2(0, 1, A, B, Offset).
+asm(_, store_word(A, B, Offset)) --> !, instruction_format_F2(1, 0, A, B, Offset).
+asm(_, store_byte(A, B, Offset)) --> !, instruction_format_F2(1, 1, A, B, Offset).
+
+asm(_, mov(A, C)) --> instruction_format_F0(0, A, 0, mov, C).
+asm(_, mov_with_shift(A, C)) --> instruction_format_F0(1, A, 0, mov, C).
+
+asm(_, mov_imm_with_shift(A, Imm)) --> {pos_int16(Imm)}, !, instruction_format_F1(1, 0, A, 0, mov, Imm).
+asm(_, mov_imm_with_shift(A, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(1, 0, A, 0, mov, Imm).
+asm(_, mov_imm_with_shift(_, _)) --> {write('Immediate value out of bounds'), fail}.
+
+asm(_, mov_imm(A, Imm) ) --> {pos_int16(Imm)}, !, instruction_format_F1(0, 0, A, 0, mov, Imm).
+asm(_, mov_imm(A, Imm) ) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, 0, mov, Imm).
+asm(_, mov_imm(_, _) ) --> {write('Immediate value out of bounds'), fail}.
+
+asm(_, add(A, B, C)) --> instruction_format_F0(0, A, B, add, C).
+asm(_, add_carry(A, B, C)) --> instruction_format_F0(1, A, B, add, C).
+asm(_, sub(A, B, C)) --> instruction_format_F0(0, A, B, sub, C).
+asm(_, sub_carry(A, B, C)) --> instruction_format_F0(1, A, B, sub, C).
+
+asm(_, add_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, add, Imm).
+asm(_, add_imm(A, B, Imm)) --> {pos_int15(Imm)}, !, instruction_format_F1(0, 0, A, B, add, Imm).
+asm(_, add_imm_carry(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(1, 1, A, B, add, Imm).
+asm(_, add_imm_carry(A, B, Imm)) --> {pos_int15(Imm)}, !, instruction_format_F1(1, 0, A, B, add, Imm).
+asm(_, sub_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, sub, Imm).
+asm(_, sub_imm(A, B, Imm)) --> {pos_int15(Imm)}, !, instruction_format_F1(0, 0, A, B, sub, Imm).
+asm(_, sub_imm_carry(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(1, 1, A, B, sub, Imm).
+asm(_, sub_imm_carry(A, B, Imm)) --> {pos_int15(Imm)}, !, instruction_format_F1(1, 0, A, B, sub, Imm).
+
+asm(_, mul(A, B, C)) --> instruction_format_F0(0, A, B, mul, C).
+asm(_, mul_unsigned(A, B, C)) --> instruction_format_F0(1, A, B, mul, C).
+asm(_, mul_imm(A, B, Imm, U)) --> {neg_int15(Imm)}, !, instruction_format_F1(U, 1, A, B, mul, Imm).
+asm(_, mul_imm(A, B, Imm, U)) --> {pos_int15(Imm)}, !, instruction_format_F1(U, 0, A, B, mul, Imm).
+
+asm(_, and(A, B, C)) --> instruction_format_F0(0, A, B, and, C).
+asm(_, ann(A, B, C)) --> instruction_format_F0(0, A, B, ann, C).
+asm(_, asr(A, B, C)) --> instruction_format_F0(0, A, B, asr, C).
+asm(_, div(A, B, C)) --> instruction_format_F0(0, A, B, div, C).
+asm(_, ior(A, B, C)) --> instruction_format_F0(0, A, B, ior, C).
+asm(_, lsl(A, B, C)) --> instruction_format_F0(0, A, B, lsl, C).
+asm(_, ror(A, B, C)) --> instruction_format_F0(0, A, B, ror, C).
+asm(_, xor(A, B, C)) --> instruction_format_F0(0, A, B, xor, C).
+
+asm(_, and_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, and, Imm).
+asm(_, and_imm(A, B, Imm)) --> {pos_int16(Imm)}, !, instruction_format_F1(0, 0, A, B, and, Imm).
+asm(_, ann_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, ann, Imm).
+asm(_, ann_imm(A, B, Imm)) --> {pos_int16(Imm)}, !, instruction_format_F1(0, 0, A, B, ann, Imm).
+asm(_, asr_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, asr, Imm).
+asm(_, asr_imm(A, B, Imm)) --> {pos_int16(Imm)}, !, instruction_format_F1(0, 0, A, B, asr, Imm).
+asm(_, div_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, div, Imm).
+asm(_, div_imm(A, B, Imm)) --> {pos_int16(Imm)}, !, instruction_format_F1(0, 0, A, B, div, Imm).
+asm(_, ior_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, ior, Imm).
+asm(_, ior_imm(A, B, Imm)) --> {pos_int16(Imm)}, !, instruction_format_F1(0, 0, A, B, ior, Imm).
+asm(_, lsl_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, lsl, Imm).
+asm(_, lsl_imm(A, B, Imm)) --> {pos_int16(Imm)}, !, instruction_format_F1(0, 0, A, B, lsl, Imm).
+asm(_, ror_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, ror, Imm).
+asm(_, ror_imm(A, B, Imm)) --> {pos_int16(Imm)}, !, instruction_format_F1(0, 0, A, B, ror, Imm).
+asm(_, xor_imm(A, B, Imm)) --> {neg_int15(Imm)}, !, instruction_format_F1(0, 1, A, B, xor, Imm).
+asm(_, xor_imm(A, B, Imm)) --> {pos_int16(Imm)}, !, instruction_format_F1(0, 0, A, B, xor, Imm).
+
+asm(_, cc(C)) --> instruction_format_F3a(0, cc, C).
+asm(N, cc_offset(Label)) --> instruction_format_F3b(0, cc, Label, N).
+asm(_, cc_link(C)) --> instruction_format_F3a(1, cc, C).
+asm(N, cc_link_offset(Label)) --> instruction_format_F3b(1, cc, Label, N).
+asm(_, cs(C)) --> instruction_format_F3a(0, cs, C).
+asm(N, cs_offset(Label)) --> instruction_format_F3b(0, cs, Label, N).
+asm(_, cs_link(C)) --> instruction_format_F3a(1, cs, C).
+asm(N, cs_link_offset(Label)) --> instruction_format_F3b(1, cs, Label, N).
+asm(_, do(C)) --> instruction_format_F3a(0, do, C).
+asm(N, do_offset(Label)) --> instruction_format_F3b(0, do, Label, N).
+asm(_, do_link(C)) --> instruction_format_F3a(1, do, C).
+asm(N, do_link_offset(Label)) --> instruction_format_F3b(1, do, Label, N).
+asm(_, eq(C)) --> instruction_format_F3a(0, eq, C).
+asm(N, eq_offset(Label)) --> instruction_format_F3b(0, eq, Label, N).
+asm(_, eq_link(C)) --> instruction_format_F3a(1, eq, C).
+asm(N, eq_link_offset(Label)) --> instruction_format_F3b(1, eq, Label, N).
+asm(_, ge(C)) --> instruction_format_F3a(0, ge, C).
+asm(N, ge_offset(Label)) --> instruction_format_F3b(0, ge, Label, N).
+asm(_, ge_link(C)) --> instruction_format_F3a(1, ge, C).
+asm(N, ge_link_offset(Label)) --> instruction_format_F3b(1, ge, Label, N).
+asm(_, gt(C)) --> instruction_format_F3a(0, gt, C).
+asm(N, gt_offset(Label)) --> instruction_format_F3b(0, gt, Label, N).
+asm(_, gt_link(C)) --> instruction_format_F3a(1, gt, C).
+asm(N, gt_link_offset(Label)) --> instruction_format_F3b(1, gt, Label, N).
+asm(_, hi(C)) --> instruction_format_F3a(0, hi, C).
+asm(N, hi_offset(Label)) --> instruction_format_F3b(0, hi, Label, N).
+asm(_, hi_link(C)) --> instruction_format_F3a(1, hi, C).
+asm(N, hi_link_offset(Label)) --> instruction_format_F3b(1, hi, Label, N).
+asm(_, le(C)) --> instruction_format_F3a(0, le, C).
+asm(N, le_offset(Label)) --> instruction_format_F3b(0, le, Label, N).
+asm(_, le_link(C)) --> instruction_format_F3a(1, le, C).
+asm(N, le_link_offset(Label)) --> instruction_format_F3b(1, le, Label, N).
+asm(_, ls(C)) --> instruction_format_F3a(0, ls, C).
+asm(N, ls_offset(Label)) --> instruction_format_F3b(0, ls, Label, N).
+asm(_, ls_link(C)) --> instruction_format_F3a(1, ls, C).
+asm(N, ls_link_offset(Label)) --> instruction_format_F3b(1, ls, Label, N).
+asm(_, lt(C)) --> instruction_format_F3a(0, lt, C).
+asm(N, lt_offset(Label)) --> instruction_format_F3b(0, lt, Label, N).
+asm(_, lt_link(C)) --> instruction_format_F3a(1, lt, C).
+asm(N, lt_link_offset(Label)) --> instruction_format_F3b(1, lt, Label, N).
+asm(_, mi(C)) --> instruction_format_F3a(0, mi, C).
+asm(N, mi_offset(Label)) --> instruction_format_F3b(0, mi, Label, N).
+asm(_, mi_link(C)) --> instruction_format_F3a(1, mi, C).
+asm(N, mi_link_offset(Label)) --> instruction_format_F3b(1, mi, Label, N).
+asm(_, ne(C)) --> instruction_format_F3a(0, ne, C).
+asm(N, ne_offset(Label)) --> instruction_format_F3b(0, ne, Label, N).
+asm(_, ne_link(C)) --> instruction_format_F3a(1, ne, C).
+asm(N, ne_link_offset(Label)) --> instruction_format_F3b(1, ne, Label, N).
+asm(_, nv(C)) --> instruction_format_F3a(0, nv, C). % NeVer.
+asm(N, nv_offset(Label)) --> instruction_format_F3b(0, nv, Label, N).
+asm(_, nv_link(C)) --> instruction_format_F3a(1, nv, C).
+asm(N, nv_link_offset(Label)) --> instruction_format_F3b(1, nv, Label, N).
+asm(_, pl(C)) --> instruction_format_F3a(0, pl, C).
+asm(N, pl_offset(Label)) --> instruction_format_F3b(0, pl, Label, N).
+asm(_, pl_link(C)) --> instruction_format_F3a(1, pl, C).
+asm(N, pl_link_offset(Label)) --> instruction_format_F3b(1, pl, Label, N).
+asm(_, vc(C)) --> instruction_format_F3a(0, vc, C).
+asm(N, vc_offset(Label)) --> instruction_format_F3b(0, vc, Label, N).
+asm(_, vc_link(C)) --> instruction_format_F3a(1, vc, C).
+asm(N, vc_link_offset(Label)) --> instruction_format_F3b(1, vc, Label, N).
+asm(_, vs(C)) --> instruction_format_F3a(0, vs, C).
+asm(N, vs_offset(Label)) --> instruction_format_F3b(0, vs, Label, N).
+asm(_, vs_link(C)) --> instruction_format_F3a(1, vs, C).
+asm(N, vs_link_offset(Label)) --> instruction_format_F3b(1, vs, Label, N).
+
+% This is the core of the assembler where the instruction formats are specified.
+
+instruction_format_F0(U, A, B, Op, C ) --> [0, 0, U, 0], reg(A), reg(B), operation(Op), skip(12), reg(C).
+instruction_format_F1(U, V, A, B, Op, Im) --> [0, 1, U, V], reg(A), reg(B), operation(Op), immediate(Im).
+instruction_format_F2(U, V, A, B, Offset) --> [1, 0, U, V], reg(A), reg(B), offset(Offset).
+instruction_format_F3a(V, Cond, C ) --> [1, 1, 0, V], cond(Cond), skip(20), reg(C).
+instruction_format_F3b(V, Cond, To, Here) --> [1, 1, 1, V], cond(Cond), encode_jump_offset(To, Here).
+
+immediate(Imm) --> encode_int(16, Imm), !.
+offset(Offset) --> encode_int(20, Offset), !.
+
+skip(N) --> collect(N, Zeros), {Zeros ins 0..0}.
+
+encode_jump_offset(To, Here) --> {Offset is ((To - Here) >> 2) - 1}, encode_int(24, Offset).
+
+encode_int(Width, I) --> {I >= 0}, !, collect(Width, Bits), { binary_number(Bits, I) }, !.
+encode_int(Width, I) --> {I < 0}, !, collect(Width, Bits), {twos_compliment(Bits, I, Width)}, !.
+
+collect(N, []) --> {N =< 0}.
+collect(N, [X|Rest]) --> {N > 0, N0 is N - 1}, [X], collect(N0, Rest).
+
+reg( 0) --> [0, 0, 0, 0].
+reg( 1) --> [0, 0, 0, 1].
+reg( 2) --> [0, 0, 1, 0].
+reg( 3) --> [0, 0, 1, 1].
+reg( 4) --> [0, 1, 0, 0].
+reg( 5) --> [0, 1, 0, 1].
+reg( 6) --> [0, 1, 1, 0].
+reg( 7) --> [0, 1, 1, 1].
+reg( 8) --> [1, 0, 0, 0].
+reg( 9) --> [1, 0, 0, 1].
+reg(10) --> [1, 0, 1, 0].
+reg(11) --> [1, 0, 1, 1].
+reg(12) --> [1, 1, 0, 0].
+reg(13) --> [1, 1, 0, 1].
+reg(14) --> [1, 1, 1, 0].
+reg(15) --> [1, 1, 1, 1].
+
+operation(mov) --> [0, 0, 0, 0].
+operation(lsl) --> [0, 0, 0, 1].
+operation(asr) --> [0, 0, 1, 0].
+operation(ror) --> [0, 0, 1, 1].
+operation(and) --> [0, 1, 0, 0].
+operation(ann) --> [0, 1, 0, 1].
+operation(ior) --> [0, 1, 1, 0].
+operation(xor) --> [0, 1, 1, 1].
+operation(add) --> [1, 0, 0, 0].
+operation(sub) --> [1, 0, 0, 1].
+operation(mul) --> [1, 0, 1, 0].
+operation(div) --> [1, 0, 1, 1].
+operation(fad) --> [1, 1, 0, 0].
+operation(fsb) --> [1, 1, 0, 1].
+operation(fml) --> [1, 1, 1, 0].
+operation(fdv) --> [1, 1, 1, 1].
+
+cond(mi) --> [0, 0, 0, 0].
+cond(eq) --> [0, 0, 0, 1].
+cond(cs) --> [0, 0, 1, 0].
+cond(vs) --> [0, 0, 1, 1].
+cond(ls) --> [0, 1, 0, 0].
+cond(lt) --> [0, 1, 0, 1].
+cond(le) --> [0, 1, 1, 0].
+cond(do) --> [0, 1, 1, 1].
+cond(pl) --> [1, 0, 0, 0].
+cond(ne) --> [1, 0, 0, 1].
+cond(cc) --> [1, 0, 1, 0].
+cond(vc) --> [1, 0, 1, 1].
+cond(hi) --> [1, 1, 0, 0].
+cond(ge) --> [1, 1, 0, 1].
+cond(gt) --> [1, 1, 1, 0].
+cond(nv) --> [1, 1, 1, 1].
+
+pos_int16(I) :- I >= 0, I < 2^16.
+pos_int15(I) :- I >= 0, I < 2^15.
+neg_int15(I) :- I < 0, I >= -(2^15).
+int15(I) :- pos_int15(I) ; neg_int15(I).
+
+
+invert([], []).
+invert([1|Tail], [0|Lait]) :- invert(Tail, Lait).
+invert([0|Tail], [1|Lait]) :- invert(Tail, Lait).
+
+twos_compliment(Bits, Number, Width) :-
+ X is abs(Number),
+ binary_number(B, X),
+ length(B, Width),
+ invert(B, Antibits),
+ binary_number(Antibits, Y),
+ Z is Y+1,
+ length(Bits, Width),
+ binary_number(Bits, Z).
+
+% https://stackoverflow.com/a/28015816
+
+canonical_binary_number([0], 0).
+canonical_binary_number([1], 1).
+canonical_binary_number([1|Bits], Number):-
+ when(ground(Number),
+ (Number > 1,
+ Pow is floor(log(Number) / log(2)),
+ Number1 is Number - 2 ^ Pow,
+ ( Number1 > 1
+ -> Pow1 is floor(log(Number1) / log(2)) + 1
+ ; Pow1 = 1
+ ))),
+ length(Bits, Pow),
+ between(1, Pow, Pow1),
+ length(Bits1, Pow1),
+ append(Zeros, Bits1, Bits),
+ maplist(=(0), Zeros),
+ canonical_binary_number(Bits1, Number1),
+ Number is Number1 + 2 ^ Pow.
+
+binary_number( Bits , Number) :- canonical_binary_number(Bits, Number).
+binary_number([0|Bits], Number) :- binary_number(Bits, Number).
+
+
+% Helper code to write the list of bits as a binary file.
+
+for_serial(Binary, Ser) :-
+ length(Binary, LengthInBits),
+ LengthInBytes is LengthInBits >> 3,
+ skip(32, Caboose, []), % zero word to signal EOF to bootloader.
+ append(Binary, Caboose, B),
+ skip(32, G, B), % Address is zero.
+ binary_number(Bits, LengthInBytes),
+ collect(32, Bits, Ser, G).
+
+write_binary(Name, Binary) :-
+ open(Name, write, Stream, [type(binary)]),
+ for_serial(Binary, Ser),
+ phrase(write_binary_(Stream), Ser),
+ close(Stream).
+
+write_binary_(Stream) -->
+ % Handle "Endian-ness".
+ collect(8, Bits3), collect(8, Bits2), collect(8, Bits1), collect(8, Bits0), !,
+ {wb(Bits0, Stream), wb(Bits1, Stream), wb(Bits2, Stream), wb(Bits3, Stream)},
+ write_binary_(Stream).
+write_binary_(_) --> [].
+
+wb(Bits, Stream) :- binary_number(Bits, Byte), put_byte(Stream, Byte).
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