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Merge pull request #886 from diffblue/xnor1
Verilog: implement xnor gates
2 parents 003138b + 13d7d6a commit 268e27e

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8 files changed

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‎regression/verilog/primitive_gates/xnor1.desc‎

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CORE broken-smt-backend
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xnor1.sv
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--bound 0
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^\[main\.xnor_ok\] always !\(xor\(xor\(main\.xnor_in1, main\.xnor_in2\), main\.xnor_in3\)\) == main\.xnor_out: PROVED up to bound 0$
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^\[main\.xnor_fail\] always main\.xnor_in1 == main\.xnor_in2 == main\.xnor_in3 == main\.xnor_out: REFUTED$
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^\[main\.xnor_is_reduction_xnor\] always ~\^\{ main\.xnor_in1, main\.xnor_in2, main\.xnor_in3 \} == main\.xnor_out: PROVED up to bound 0$
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^EXIT=10$
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^SIGNAL=0$
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--
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^warning: ignoring
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--

‎regression/verilog/primitive_gates/xnor1.sv‎

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module main(output xnor_out, input xnor_in1, xnor_in2, xnor_in3);
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// An 'xnor' with three inputs.
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// 1800-2017 28.4 says that these "shall have a natural extension".
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xnor x1(xnor_out, xnor_in1, xnor_in2, xnor_in3);
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// should pass
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`ifndef __ICARUS__
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xnor_ok: assert final (!(xnor_in1 ^ xnor_in2 ^ xnor_in3)==xnor_out);
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`endif
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// should fail -- not the same as using a chain of binary xnors
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`ifndef __ICARUS__
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xnor_fail: assert final ((xnor_in1 ~^ xnor_in2 ~^ xnor_in3)==xnor_out);
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`endif
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// should pass -- xnor is the same as reduction xnor
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`ifndef __ICARUS__
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xnor_is_reduction_xnor: assert final (~^{xnor_in1, xnor_in2, xnor_in3}==xnor_out);
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`endif
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endmodule
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// To check simulator behavior
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module xnor_tb;
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wire xnor_out;
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reg xnor_in1, xnor_in2, xnor_in3;
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main m(xnor_out, xnor_in1, xnor_in2, xnor_in3);
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task print;
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begin
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$display("input: ", xnor_in1, xnor_in2, xnor_in3);
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$display(" xnor gate: ", xnor_out);
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$display(" reduction-xnor: ", ~^{xnor_in1, xnor_in2, xnor_in3});
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$display(" !reduction-xor: ", !(^{xnor_in1, xnor_in2, xnor_in3}));
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$display(" !xor: ", !(xnor_in1 ^ xnor_in2 ^ xnor_in3));
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$display(" binary xnors: ", xnor_in1 ~^ xnor_in2 ~^ xnor_in3);
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end
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endtask
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initial begin
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{xnor_in1, xnor_in2, xnor_in3} = 'b000;
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#1;
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print();
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{xnor_in1, xnor_in2, xnor_in3} = 'b100;
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#1;
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print();
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{xnor_in1, xnor_in2, xnor_in3} = 'b110;
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#1;
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print();
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{xnor_in1, xnor_in2, xnor_in3} = 'b111;
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#1;
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print();
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{xnor_in1, xnor_in2, xnor_in3} = 'b101;
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#1;
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print();
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end
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endmodule

‎regression/verilog/primitive_gates/xnor2.desc‎

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CORE broken-smt-backend
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xnor2.sv
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--bound 0
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^\[main\.xnor_ok\] always !main\.xnor_in1 == main\.xnor_out: PROVED up to bound 0$
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^\[main\.xnor_is_reduction_xnor\] always ~\^\{ main\.xnor_in1 \} == main\.xnor_out: PROVED up to bound 0$
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^EXIT=0$
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^SIGNAL=0$
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--
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^warning: ignoring
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--

‎regression/verilog/primitive_gates/xnor2.sv‎

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module main(output xnor_out, input xnor_in1);
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// An 'xnor' with just one input. These negate.
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xnor x1(xnor_out, xnor_in1);
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// should pass
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`ifndef __ICARUS__
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xnor_ok: assert final (!xnor_in1==xnor_out);
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`endif
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// should pass -- xnor is the same as reduction xnor
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`ifndef __ICARUS__
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xnor_is_reduction_xnor: assert final (~^{xnor_in1}==xnor_out);
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`endif
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endmodule
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// To check simulator behavior
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module xnor_tb;
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wire xnor_out;
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reg xnor_in1;
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main m(xnor_out, xnor_in1);
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task print;
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begin
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$display("input: ", xnor_in1);
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$display(" xnor gate: ", xnor_out);
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$display(" reduction-xnor: ", ~^{xnor_in1});
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$display(" !reduction-xor: ", !(^{xnor_in1}));
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$display(" !: ", !xnor_in1);
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end
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endtask
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initial begin
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{xnor_in1} = 'b0;
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#1;
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print();
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{xnor_in1} = 'b1;
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#1;
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print();
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end
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endmodule

‎regression/verilog/primitive_gates/xnor3.desc‎

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CORE broken-smt-backend
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xnor3.sv
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--bound 0
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^\[main\.xnor_ok\] always main\.xnor_in1 ~\^ main\.xnor_in2 == main\.xnor_out: PROVED up to bound 0$
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^EXIT=0$
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^SIGNAL=0$
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--
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^warning: ignoring
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--

‎regression/verilog/primitive_gates/xnor3.sv‎

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module main(output [31:0] xnor_out, input [31:0] xnor_in1, xnor_in2);
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// An 'xnor' with two inputs, 32 bits each.
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xnor x1[31:0](xnor_out, xnor_in1, xnor_in2);
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// should pass
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`ifndef __ICARUS__
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xnor_ok: assert final (xnor_in1 ~^ xnor_in2==xnor_out);
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`endif
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endmodule

‎src/verilog/parser.y‎

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@@ -2724,7 +2724,7 @@ n_input_gatetype:
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| TOK_NAND { init($$, ID_nand); }
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| TOK_NOR { init($$, ID_nor); }
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| TOK_OR { init($$, ID_or); }
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| TOK_XNOR { init($$, ID_nor); }
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| TOK_XNOR { init($$, ID_xnor); }
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| TOK_XOR { init($$, ID_xor); }
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;
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‎src/verilog/verilog_synthesis.cpp‎

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@@ -1516,12 +1516,9 @@ void verilog_synthesist::synth_module_instance_builtin(
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assert(trans.operands().size()==3);
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trans.invar().add_to_operands(std::move(constraint));
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}
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else if(module==ID_and ||
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module==ID_nand ||
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module==ID_or ||
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module==ID_nor ||
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module==ID_xor ||
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module==ID_xnor)
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else if(
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module == ID_and || module == ID_nand || module == ID_or ||
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module == ID_nor || module == ID_xor)
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{
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// 1800-2017 28.4 and, nand, nor, or, xor, and xnor gates
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DATA_INVARIANT(
@@ -1549,6 +1546,41 @@ void verilog_synthesist::synth_module_instance_builtin(
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equal_exprt constraint{output, op};
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trans.invar().add_to_operands(std::move(constraint));
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}
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else if(module == ID_xnor)
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{
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// Our solver does not have ID_xnor, hence use the negation of ID_xor
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// ID_bitxor.
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// With one operand, or with more than three operands, the result is
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// ambiguous. The semantics of bitxnor do not match when using one
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// or more than two operands.
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DATA_INVARIANT(
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instance.connections().size() >= 2,
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"binary primitive gates should have at least two connections");
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// One output, one or more inputs.
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auto &connections = instance.connections();
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auto &output = connections[0];
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exprt::operandst operands;
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// iterate over the module inputs
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for(std::size_t i = 1; i < connections.size(); i++)
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{
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operands.push_back(connections[i]);
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}
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exprt op;
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if(instance.type().id() == ID_bool)
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op = not_exprt{
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multi_ary_exprt{ID_xor, std::move(operands), instance.type()}};
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else
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op = bitnot_exprt{
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multi_ary_exprt{ID_bitxor, std::move(operands), instance.type()}};
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equal_exprt constraint{output, std::move(op)};
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trans.invar().add_to_operands(std::move(constraint));
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}
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else if(module==ID_buf)
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{
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assert(instance.connections().size() >= 2);

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