| Line 88... |
Line 88... |
cntlz128Reg u4 (.clk(clk), .ce(ce), .i(bcd), .o(lz) );
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cntlz128Reg u4 (.clk(clk), .ce(ce), .i(bcd), .o(lz) );
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always_comb
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always_comb
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lz4 = lz >> 2'd2;
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lz4 = lz >> 2'd2;
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assign wd = zeroXp - 8'd1 + 8'd25 - lz4 + 8'd9; // constant except for lz
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assign wd = zeroXp - 8'd1 + 8'd25 - lz4 + 8'd7; // constant except for lz
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reg [11:0] xo;
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reg [11:0] xo;
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always_ff @(posedge clk)
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always_ff @(posedge clk)
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xo <= iz ? 'd0 : wd;
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xo <= iz ? 'd0 : wd;
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| Line 102... |
Line 102... |
// right shift is required. There are only about 114 bits of precision, but the
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// right shift is required. There are only about 114 bits of precision, but the
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// incoming number is allowed to be 128-bit.
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// incoming number is allowed to be 128-bit.
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// Rounding is required only when the number needs to be right-shifted.
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// Rounding is required only when the number needs to be right-shifted.
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always_ff @(posedge clk)
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always_ff @(posedge clk)
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if (lz4 < 8'd9)
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if (lz4 < 8'd7)
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simag = bcd1 >> {8'd9 - lz4,2'd0};
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simag = bcd1 >> {8'd7 - lz4,2'd0};
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else
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else
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simag = bcd1 << {lz4 - 8'd9,2'd0};
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simag = bcd1 << {lz4 - 8'd7,2'd0};
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wire g = bcd1[{8'd9 - lz4,2'd0}]; // guard bit (lsb)
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wire g = bcd1[{8'd7 - lz4,2'd0}]; // guard bit (lsb)
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wire r = bcd1[{8'd9 - lz4,2'd0}-1]; // rounding bit
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wire r = bcd1[{8'd7 - lz4,2'd0}-1]; // rounding bit
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wire s = |(bcd1 & (128'd1 << {8'd9 - lz4,2'd0}-2) - 2'd1); // "sticky" bit
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wire s = |(bcd1 & (128'd1 << {8'd7 - lz4,2'd0}-2) - 2'd1); // "sticky" bit
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reg rnd;
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reg rnd;
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// Compute the round bit
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// Compute the round bit
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always_ff @(posedge clk)
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always_ff @(posedge clk)
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if (lz4 < 8'd9)
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if (lz4 < 8'd7)
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case (rmd)
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case (rmd)
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3'd0: rnd = (g & r) | (r & s); // round to nearest even
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3'd0: rnd = (g & r) | (r & s); // round to nearest even
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3'd1: rnd = 0; // round to zero (truncate)
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3'd1: rnd = 0; // round to zero (truncate)
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3'd2: rnd = (r | s) & !so; // round towards +infinity
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3'd2: rnd = (r | s) & !so; // round towards +infinity
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3'd3: rnd = (r | s) & so; // round towards -infinity
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3'd3: rnd = (r | s) & so; // round towards -infinity
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