cc_lerp_booth8.v
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////////////////////////////////////////////////////////////////////////
//
// Project Reality
//
// module: cc_lerp_booth8
// description: Pseudo-Booth encoder for lerp for color combine unit.
// Generates bit 8 partial product. This does one partial
// for lerp subtract/multiply. This effectively does the
// subtract without propagating the carries. The negative
// input is first 1's complemented, then the two inputs are
// considered bitwise. If none is set, mask out the multiply
// input. If one bit is set, pass the mpy input as a partial
// product. If both bits are set, shift up one bit.
// This implements the "Akeley" interpretation of the
// subtract inputs. The 9 bit inputs treated as unsigned if
// the 2 msb's are 10, else are sign extended before
// the subtract, and all 10 bits of result are used in the
// multiply by the other 9 bit input.
//
// designer: Phil Gossett
// date: 6/25/94
//
////////////////////////////////////////////////////////////////////////
module cc_lerp_booth8 (x7, x8, y7, y8, a, p);
input x7;
input x8;
input y7;
input y8;
input [8:0] a;
wire [8:0] pp;
output [8:0] p; // pseudo-booth encoded partial product
xo02d1h xor8xx (.z(xx), .a1(x7), .a2(x8)); // Akeley interpretation
xo02d1h xor8yy (.z(yy), .a1(y7), .a2(y8));
fn05d2 mux8s0 (.zn(msel), .a1(yy), .b1(xx)); // msel = (y7^y8) && !(x7^x8)
fn01d2 mux8e0 (.zn(menb), .a1(yy), .b1(xx)); // menb = (y7^y8) || !(x7^x8)
mx21d1h mux8b0 (.s(msel), .i0(a[0]), .i1(1'b0), .z(pp[0]));
mx21d1h mux8b1 (.s(msel), .i0(a[1]), .i1(a[0]), .z(pp[1]));
mx21d1h mux8b2 (.s(msel), .i0(a[2]), .i1(a[1]), .z(pp[2]));
mx21d1h mux8b3 (.s(msel), .i0(a[3]), .i1(a[2]), .z(pp[3]));
mx21d1h mux8b4 (.s(msel), .i0(a[4]), .i1(a[3]), .z(pp[4]));
mx21d1h mux8b5 (.s(msel), .i0(a[5]), .i1(a[4]), .z(pp[5]));
mx21d1h mux8b6 (.s(msel), .i0(a[6]), .i1(a[5]), .z(pp[6]));
mx21d1h mux8b7 (.s(msel), .i0(a[7]), .i1(a[6]), .z(pp[7]));
mx21d1h mux8b8 (.s(msel), .i0(a[8]), .i1(a[7]), .z(pp[8]));
// msb falls off end
nd02d1 and8b0 (.a1(menb), .a2(pp[0]), .zn(p[0]));
nd02d1 and8b1 (.a1(menb), .a2(pp[1]), .zn(p[1]));
nd02d1 and8b2 (.a1(menb), .a2(pp[2]), .zn(p[2]));
nd02d1 and8b3 (.a1(menb), .a2(pp[3]), .zn(p[3]));
nd02d1 and8b4 (.a1(menb), .a2(pp[4]), .zn(p[4]));
nd02d1 and8b5 (.a1(menb), .a2(pp[5]), .zn(p[5]));
nd02d1 and8b6 (.a1(menb), .a2(pp[6]), .zn(p[6]));
nd02d1 and8b7 (.a1(menb), .a2(pp[7]), .zn(p[7]));
nd02d1 and8b8 (.a1(menb), .a2(pp[8]), .zn(p[8]));
endmodule // cc_lerp_booth8