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fix multiply signed_overflow bug (only for serial multiplier) r1 #107

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fix multiply signed_overflow bug (only for serial multiplier) r1 #107

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0edd737
fix multiply signed_overflow bug (only for serial multiplier)
JaewonHur Dec 19, 2019
374f906
fix multiply signed_overflow bug (only for serial multiplier) r1
JaewonHur Dec 19, 2019
c0843f7
fix multiply signed_overflow bug, handle the case when one of the ope…
JaewonHur Dec 22, 2019
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31 changes: 18 additions & 13 deletions rtl/verilog/mor1kx_execute_alu.v
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Original file line number Diff line number Diff line change
Expand Up @@ -285,6 +285,7 @@ endgenerate

// Can't detect unsigned overflow in this implementation
assign mul_unsigned_overflow = 0;
assign mul_signed_overflow = 0;

end // if (FEATURE_MULTIPLIER=="PIPELINED")
else if (FEATURE_MULTIPLIER=="SERIAL") begin : serialmultiply
Expand Down Expand Up @@ -379,6 +380,7 @@ endgenerate
assign mul_result = 0;
assign mul_valid = 1'b1;
assign mul_unsigned_overflow = 0;
assign mul_signed_overflow = 0;
end
else begin
// Incorrect configuration option
Expand All @@ -390,19 +392,22 @@ endgenerate
end
endgenerate

// One signed overflow detection for all multiplication implmentations
assign mul_signed_overflow = (FEATURE_MULTIPLIER=="NONE") ||
(FEATURE_MULTIPLIER=="PIPELINED") ? 1'b0 :
// Same signs, check for negative result
// (should be positive)
((a[OPTION_OPERAND_WIDTH-1] ==
b[OPTION_OPERAND_WIDTH-1]) &&
mul_result[OPTION_OPERAND_WIDTH-1]) ||
// Differring signs, check for positive result
// (should be negative)
((a[OPTION_OPERAND_WIDTH-1] ^
b[OPTION_OPERAND_WIDTH-1]) &&
!mul_result[OPTION_OPERAND_WIDTH-1]);
// One signed overflow detection for all multiplication implmentations
assign mul_signed_overflow = (FEATURE_MULTIPLIER=="NONE") ||
(FEATURE_MULTIPLIER=="PIPELINED") ? 1'b0 :
// When either a or b is 0, result should not
// be negative
((a == 0 || b == 0) && mul_result[OPTION_OPERAND_WIDTH-1]) ||
// Same signs, check for negative result
// (should be positive)
((a[OPTION_OPERAND_WIDTH-1] ==
b[OPTION_OPERAND_WIDTH-1]) &&
mul_result[OPTION_OPERAND_WIDTH-1]) ||
// Differring signs, check for positive result
// (should be negative)
((a[OPTION_OPERAND_WIDTH-1] ^
b[OPTION_OPERAND_WIDTH-1]) &&
!mul_result[OPTION_OPERAND_WIDTH-1]);

assign mul_result_o = mul_result;

Expand Down