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// -*- verilog -*-
//
// USRP - Universal Software Radio Peripheral
//
// Copyright (C) 2011 Matt Ettus
//
//
// Rounding "macro"
// Keeps the topmost bits, does proper 2s comp round to zero (unbiased truncation)
module round
#(parameter bits_in=0,
parameter bits_out=0,
parameter round_to_zero=0, // original behavior
parameter round_to_nearest=1, // lowest noise
parameter trunc=0) // round to negative infinity
(input [bits_in-1:0] in,
output [bits_out-1:0] out,
output [bits_in-bits_out:0] err);
wire round_corr,round_corr_trunc,round_corr_rtz,round_corr_nearest,round_corr_nearest_safe;
assign round_corr_trunc = 0;
assign round_corr_rtz = (in[bits_in-1] & |in[bits_in-bits_out-1:0]);
assign round_corr_nearest = in[bits_in-bits_out-1];
generate
if(bits_in-bits_out > 1)
assign round_corr_nearest_safe = (~in[bits_in-1] & (&in[bits_in-2:bits_out])) ? 0 :
round_corr_nearest;
else
assign round_corr_nearest_safe = round_corr_nearest;
endgenerate
assign round_corr = round_to_nearest ? round_corr_nearest_safe :
trunc ? round_corr_trunc :
round_to_zero ? round_corr_rtz :
0; // default to trunc
assign out = in[bits_in-1:bits_in-bits_out] + round_corr;
assign err = in - {out,{(bits_in-bits_out){1'b0}}};
endmodule // round
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