riscv/rocket-chip
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simplify and improve multiplier

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This commit is contained in:
Andrew Waterman 2012-10-06 17:32:01 -07:00
parent 1864e41361
commit 27ddff1adb
2 changed files with 17 additions and 40 deletions
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2
rocket/src/main/scala/dpath.scala
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@ -252,7 +252,7 @@ class rocketDpath extends Component
io.ctrl.div_result_val := div.io.resp_val io.ctrl.div_result_val := div.io.resp_val
// multiplier // multiplier
var mul_io = new rocketMultiplier().io var mul_io = new rocketMultiplier(unroll = 6).io
if (HAVE_VEC) if (HAVE_VEC)
{ {
val vu_mul = new rocketVUMultiplier(nwbq = 1) val vu_mul = new rocketVUMultiplier(nwbq = 1)

55
rocket/src/main/scala/multiplier.scala
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@ -61,17 +61,12 @@ class rocketVUMultiplier(nwbq: Int) extends Component {
io.vu.req <> io.cpu.req io.vu.req <> io.cpu.req
} }
class rocketMultiplier extends Component { class rocketMultiplier(unroll: Int = 1) extends Component {
val io = new ioMultiplier val io = new ioMultiplier
// w must be even (booth).
// we need an extra bit to handle signed vs. unsigned,
// so we need to add a second to keep w even.
val w = 64 + 2
val unroll = 3
require(w % 2 == 0 && (w/2) % unroll == 0) val w0 = io.req.bits.in0.getWidth
val w = (w0+1+unroll-1)/unroll*unroll
val cycles = w/unroll/2 val cycles = w/unroll
val r_val = Reg(resetVal = Bool(false)); val r_val = Reg(resetVal = Bool(false));
val r_dw = Reg { Bits() } val r_dw = Reg { Bits() }
@ -85,15 +80,15 @@ class rocketMultiplier extends Component {
val dw = io.req.bits.fn(io.req.bits.fn.width-1) val dw = io.req.bits.fn(io.req.bits.fn.width-1)
val fn = io.req.bits.fn(io.req.bits.fn.width-2,0) val fn = io.req.bits.fn(io.req.bits.fn.width-2,0)
val lhs_msb = Mux(dw === DW_64, io.req.bits.in0(63), io.req.bits.in0(31)).toBool val lhs_msb = Mux(dw === DW_64, io.req.bits.in0(w0-1), io.req.bits.in0(w0/2-1)).toBool
val lhs_sign = ((fn === MUL_H) || (fn === MUL_HSU)) && lhs_msb val lhs_sign = ((fn === MUL_H) || (fn === MUL_HSU)) && lhs_msb
val lhs_hi = Mux(dw === DW_64, io.req.bits.in0(63,32), Fill(32, lhs_sign)) val lhs_hi = Mux(dw === DW_64, io.req.bits.in0(w0-1,w0/2), Fill(w0/2, lhs_sign))
val lhs_in = Cat(lhs_sign, lhs_hi, io.req.bits.in0(31,0)) val lhs_in = Cat(lhs_sign, lhs_hi, io.req.bits.in0(w0/2-1,0))
val rhs_msb = Mux(dw === DW_64, io.req.bits.in1(63), io.req.bits.in1(31)).toBool val rhs_msb = Mux(dw === DW_64, io.req.bits.in1(w0-1), io.req.bits.in1(w0/2-1)).toBool
val rhs_sign = (fn === MUL_H) && rhs_msb val rhs_sign = (fn === MUL_H) && rhs_msb
val rhs_hi = Mux(dw === DW_64, io.req.bits.in1(63,32), Fill(32, rhs_sign)) val rhs_hi = Mux(dw === DW_64, io.req.bits.in1(w0-1,w0/2), Fill(w0/2, rhs_sign))
val rhs_in = Cat(rhs_sign, rhs_sign, rhs_hi, io.req.bits.in1(31,0)) val rhs_in = Cat(Fill(w-w0, rhs_sign), rhs_hi, io.req.bits.in1(w0/2-1,0))
val do_kill = io.req_kill && r_cnt === UFix(0) // can only kill on 1st cycle val do_kill = io.req_kill && r_cnt === UFix(0) // can only kill on 1st cycle
@ -111,34 +106,16 @@ class rocketMultiplier extends Component {
r_val := Bool(false) r_val := Bool(false)
} }
val lhs_sext = Cat(r_lhs(w-2), r_lhs(w-2), r_lhs).toUFix val sum = r_prod(2*w-1,w).toFix + r_prod(unroll-1,0).toFix * r_lhs.toFix + Mux(r_lsb, r_lhs.toFix, Fix(0))
val lhs_twice = Cat(r_lhs(w-2), r_lhs, Bits(0,1)).toUFix
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(w*2-1), prod(w*2-1,w)).toUFix
val adder_rhs = Mux(sub, ~addend, addend)
val adder_out = (adder_lhs + adder_rhs + sub.toUFix)(w,0)
lsb = prod(1)
prod = Cat(adder_out(w), adder_out, prod(w-1,2))
}
when (r_val && (r_cnt != UFix(cycles))) { when (r_val && (r_cnt != UFix(cycles))) {
r_lsb := lsb r_lsb := r_prod(unroll-1)
r_prod := prod r_prod := Cat(sum, r_prod(w-1,unroll)).toFix
r_cnt := r_cnt + UFix(1) r_cnt := r_cnt + UFix(1)
} }
val mul_output64 = Mux(r_fn === MUL_LO, r_prod(63,0), r_prod(127,64)) val mul_output64 = Mux(r_fn === MUL_LO, r_prod(w0-1,0), r_prod(2*w0-1,w0))
val mul_output32 = Mux(r_fn === MUL_LO, r_prod(31,0), r_prod(63,32)) val mul_output32 = Mux(r_fn === MUL_LO, r_prod(w0/2-1,0), r_prod(w0-1,w0/2))
val mul_output32_ext = Cat(Fill(32, mul_output32(31)), mul_output32) val mul_output32_ext = Cat(Fill(32, mul_output32(w0/2-1)), mul_output32)
val mul_output = Mux(r_dw === DW_64, mul_output64, mul_output32_ext) val mul_output = Mux(r_dw === DW_64, mul_output64, mul_output32_ext)