riscv/rocket-chip
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parameterized multiplier unrolling

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This commit is contained in:
Andrew Waterman 2011-12-20 04:18:28 -08:00
parent 733fc8e65e
commit 38ea10a5f4
1 changed files with 24 additions and 10 deletions
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34
rocket/src/main/scala/multiplier.scala
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@ -23,8 +23,14 @@ class ioMultiplier(width: Int) extends Bundle {
class rocketMultiplier extends Component {
val io = new ioMultiplier(64);
// width must be even (booth).
// we need an extra bit to handle signed vs. unsigned,
// so we need to add a second to keep width even.
val width = 64 + 2
val cycles = width/2
// unroll must divide width/2
val unroll = 3
val cycles = width/unroll/2
val r_val = Reg(resetVal = Bool(false));
val r_dw = Reg { UFix() }
@ -62,17 +68,25 @@ class rocketMultiplier extends Component {
val lhs_sext = Cat(r_lhs(width-2), r_lhs(width-2), r_lhs).toUFix
val lhs_twice = Cat(r_lhs(width-2), r_lhs, Bits(0,1)).toUFix
val addend = Mux(r_prod(0) != r_lsb, lhs_sext,
Mux(r_prod(0) != r_prod(1), lhs_twice,
UFix(0)));
val sub = r_prod(1)
val adder_lhs = Cat(r_prod(width*2-1), r_prod(width*2-1,width)).toUFix
val adder_rhs = Mux(sub, ~addend, addend)
val adder_out = (adder_lhs + adder_rhs + sub.toUFix)(width,0)
var prod = r_prod
var lsb = r_lsb
for (i <- 0 until unroll) {
val addend = Mux(prod(0) != lsb, lhs_sext,
Mux(prod(0) != prod(1), lhs_twice,
UFix(0)));
val sub = prod(1)
val adder_lhs = Cat(prod(width*2-1), prod(width*2-1,width)).toUFix
val adder_rhs = Mux(sub, ~addend, addend)
val adder_out = (adder_lhs + adder_rhs + sub.toUFix)(width,0)
lsb = prod(1)
prod = Cat(adder_out(width), adder_out, prod(width-1,2))
}
when (r_val && (r_cnt != UFix(cycles))) {
r_lsb <== r_prod(1)
r_prod <== Cat(adder_out(width), adder_out, r_prod(width-1,2))
r_lsb <== lsb
r_prod <== prod
r_cnt <== r_cnt + UFix(1)
}