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fix approximate compression
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@hansemandse
hansemandse committed Aug 31, 2023
1 parent 999cf7d commit 3b21a7e
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Showing 2 changed files with 48 additions and 44 deletions.
2 changes: 1 addition & 1 deletion src/main/scala/approx/multiplication/comptree/CompressorTree.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -218,7 +218,7 @@ private[comptree] class CompressorTree(val sig: Signature, context: Context) ext
} else {
// Otherwise, take approximate counters into account too
context.approx match {
case Miscounting(width) if cntr.approximate =>
case Miscounting(width) if isApproximate(cntr) =>
inSig.zipWithIndex.forall { case (cnt, col) =>
col <= width && inBits.colCount(lsCol + col) >= cnt }
case _ =>
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90 changes: 47 additions & 43 deletions src/main/scala/approx/multiplication/comptree/Counters.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,20 @@ private[comptree] object Counters {
*/
private[Counters] abstract class Atom(val luts: Int = -1)

/** Represents the type of a generic counter
*
* We consider two different types:
* - Exact counters that compute proper sums and carries
* - Approximate counters that compute inexact sums and carries
*/
private[Counters] abstract trait CounterType

/** Represents an exact `CounterType` */
private[Counters] trait Exact extends CounterType

/** Represents an approximate `CounterType` */
private[Counters] trait Approximate extends CounterType

/** Abstract counter class
*
* @param sig the signature of the counter
Expand All @@ -39,6 +53,8 @@ private[comptree] object Counters {
* also possess signatures that define their connectivity.
*/
abstract class Counter(val sig: (Array[Int], Array[Int]), cost: Int = -1) {
this: CounterType =>

/** The strength of the counter
*
* We use the definition by Preusser [2017]
Expand All @@ -51,28 +67,12 @@ private[comptree] object Counters {
* Intel FPGAs and ASICs.
*/
val efficiency: Double = if (cost == -1) Double.MinValue else (sig._1.sum - sig._2.sum).toDouble / cost
}

/** Whether the counter is approximation
*
* We compute and compare the needed output widths of the input and
* output signatures.
*/
lazy val approximate: Boolean = {
def computeW(signature: Array[Int]): Int = {
var sum = signature.zipWithIndex.foldLeft(BigInt(0)) { case (acc, (count, log2Weight)) =>
acc + Array.fill(count) { BigInt(0).setBit(log2Weight) }.sum
}

// Return the MSB's position
var pos = 0
while (sum > 0) {
pos += 1
sum >>= 1
}
pos
}
computeW(sig._1) == computeW(sig._2)
}
/** Returns true iff the counter mixes in `Approximate` */
def isApproximate(ctr: Counter): Boolean = ctr match {
case _: Counter with Approximate => true
case _ => false
}

/** Abstract hardware counter class
Expand Down Expand Up @@ -126,43 +126,43 @@ private[comptree] object Counters {
*/
object ASIC extends Library {
/** Counter (2 : 1,1] (half adder) */
private[ASIC] class Counter2_11 extends Counter((Array(2), Array(1, 1)), 2)
private[ASIC] class Counter2_11 extends Counter((Array(2), Array(1, 1)), 2) with Exact

/** Counter (3 : 1,1] (full adder) */
private[ASIC] class Counter3_11 extends Counter((Array(3), Array(1, 1)), 3)
private[ASIC] class Counter3_11 extends Counter((Array(3), Array(1, 1)), 3) with Exact

/** Counter (5 : 2,1] */
private[ASIC] class Counter4_21 extends Counter((Array(4), Array(1, 2)), 6)
private[ASIC] class Counter4_21 extends Counter((Array(4), Array(1, 2)), 6) with Exact

/** Approximate counter (5 : 2,1] (4:2 compressor)
*
* Implementation of the counter (design 1) from Momeni et al. [2014]
*/
private[ASIC] class Counter4_21Momeni extends Counter((Array(5), Array(1, 2)), 5)
private[ASIC] class Counter4_21Momeni extends Counter((Array(5), Array(1, 2)), 5) with Approximate

/** Approximate counter (5 : 1,1] (4:2 compressor)
*
* Implementation of the counter (design 2) from Momeni et al. [2014]
*/
private[ASIC] class Counter4_11Momeni extends Counter((Array(5), Array(1, 1)), 4)
private[ASIC] class Counter4_11Momeni extends Counter((Array(5), Array(1, 1)), 4) with Approximate

/** Approximate counter (5 : 2,1] (4:2 compressor)
*
* Implementation of the counter from Moaiyeri et al. [2017]
*/
private[ASIC] class Counter4_21Moaiyeri extends Counter((Array(5), Array(1, 2)), 4)
private[ASIC] class Counter4_21Moaiyeri extends Counter((Array(5), Array(1, 2)), 4) with Approximate

/** Counter (5 : 1,1,1] (4:2 compressor) */
private[ASIC] class Counter5_111 extends Counter((Array(5), Array(1, 1, 1)), 8)
private[ASIC] class Counter5_111 extends Counter((Array(5), Array(1, 1, 1)), 8) with Exact

/** Counter (7 : 1,1,1] */
private[ASIC] class Counter7_111 extends Counter((Array(7), Array(1, 1, 1)), 12)
private[ASIC] class Counter7_111 extends Counter((Array(7), Array(1, 1, 1)), 12) with Exact

/** Approximate counter (8 : 1,1,1]
*
* Implementation of the counter from Boroumand and Brisk [2019]
*/
private[ASIC] class Counter8_111 extends Counter((Array(8), Array(1, 1, 1)), 11)
private[ASIC] class Counter8_111 extends Counter((Array(8), Array(1, 1, 1)), 11) with Approximate

/** Collection of exact counters */
lazy val exactCounters: Seq[Counter] = Seq(
Expand Down Expand Up @@ -288,6 +288,8 @@ private[comptree] object Counters {
* - (3 : 1,1]
* - (2,5 : 1,2,1]
* - (8 : 1,1,1] (approximate)
*
* @todo Extend to support approximate compound counters.
*/
object SevenSeries extends Library {
/** Use an Atom class specific to this library to simplify type checking */
Expand All @@ -304,22 +306,22 @@ private[comptree] object Counters {
private[SevenSeries] class Atom06(val inSig: Array[Int] = Array(6, 0)) extends SevenSeriesAtom(2)

/** Counter (2 : 1,1] (half adder) */
private[SevenSeries] class Counter2_11 extends Counter((Array(2), Array(1, 1)), 1)
private[SevenSeries] class Counter2_11 extends Counter((Array(2), Array(1, 1)), 1) with Exact

/** Counter (3 : 1,1] (full adder) */
private[SevenSeries] class Counter3_11 extends Counter((Array(3), Array(1, 1)), 1)
private[SevenSeries] class Counter3_11 extends Counter((Array(3), Array(1, 1)), 1) with Exact

/** Counter (2,5 : 1,2,1]
*
* Implementation of the counter from Preusser [2017]
*/
private[SevenSeries] class Counter25_121 extends Counter((Array(5, 2), Array(1, 2, 1)), 2)
private[SevenSeries] class Counter25_121 extends Counter((Array(5, 2), Array(1, 2, 1)), 2) with Exact

/** Approximate counter (8 : 1,1,1]
*
* Implementation of the counter from Boroumand and Brisk [2019]
*/
private[SevenSeries] class Counter8_111 extends Counter((Array(8), Array(1,1,1)), 4)
private[SevenSeries] class Counter8_111 extends Counter((Array(8), Array(1,1,1)), 4) with Approximate

/** Function to compute the signature for a composed counter
*
Expand All @@ -343,7 +345,7 @@ private[comptree] object Counters {
* @param atom2 the second atom
*/
private[SevenSeries] class ComposedCounter(val atom1: SevenSeriesAtom, val atom2: SevenSeriesAtom)
extends Counter(compose(atom1, atom2), atom1.luts + atom2.luts)
extends Counter(compose(atom1, atom2), atom1.luts + atom2.luts) with Exact

/** Collection of exact counters */
lazy val exactCounters: Seq[Counter] = Seq(
Expand Down Expand Up @@ -673,6 +675,8 @@ private[comptree] object Counters {
* - (3 : 1,1]
* - (7 : 1,1,1]
* - (8 : 1,1,1] (approximate)
*
* @todo Extend to support approximate compound counters.
*/
object Versal extends Library {
/** Use an Atom class specific to this library to simplify type checking */
Expand All @@ -682,19 +686,19 @@ private[comptree] object Counters {
}

/** Counter (2 : 1,1] (half adder) */
private[Versal] class Counter2_11 extends Counter((Array(2), Array(1, 1)), 1)
private[Versal] class Counter2_11 extends Counter((Array(2), Array(1, 1)), 1) with Exact

/** Counter (3 : 1,1] (full adder) */
private[Versal] class Counter3_11 extends Counter((Array(3), Array(1, 1)), 1)
private[Versal] class Counter3_11 extends Counter((Array(3), Array(1, 1)), 1) with Exact

/** Counter (7 : 1,1,1] */
private[Versal] class Counter7_111 extends Counter((Array(7), Array(1, 1, 1)), 3)
private[Versal] class Counter7_111 extends Counter((Array(7), Array(1, 1, 1)), 3) with Exact

/** Approximate counter (8 : 1,1,1]
*
* Adaptation of the counter from Boroumand and Brisk [2019]
*/
private[Versal] class Counter8_111 extends Counter((Array(8), Array(1,1,1)), 3)
private[Versal] class Counter8_111 extends Counter((Array(8), Array(1,1,1)), 3) with Approximate

/** Function to compute the signature for a composed counter
*
Expand All @@ -718,7 +722,7 @@ private[comptree] object Counters {
* @param atom2 the second atom
*/
private[Versal] class ComposedCounter(val atom1: VersalAtom, val atom2: VersalAtom)
extends Counter(compose(atom1, atom2), atom1.luts + atom2.luts)
extends Counter(compose(atom1, atom2), atom1.luts + atom2.luts) with Exact

/** Collection of exact counters */
lazy val exactCounters: Seq[Counter] = Seq(
Expand Down Expand Up @@ -908,16 +912,16 @@ private[comptree] object Counters {
*/
object Intel extends Library {
/** Counter (2 : 1,1] (half adder) */
private[Intel] class Counter2_11 extends Counter((Array(2), Array(1, 1)), 1)
private[Intel] class Counter2_11 extends Counter((Array(2), Array(1, 1)), 1) with Exact

/** Counter (3 : 1,1] (full adder) */
private[Intel] class Counter3_11 extends Counter((Array(3), Array(1, 1)), 2)
private[Intel] class Counter3_11 extends Counter((Array(3), Array(1, 1)), 2) with Exact

/** Approximate counter (8 : 1,1,1]
*
* Implementation of the counter from Boroumand and Brisk [2019]
*/
private[Intel] class Counter8_111 extends Counter((Array(8), Array(1, 1, 1)), 4)
private[Intel] class Counter8_111 extends Counter((Array(8), Array(1, 1, 1)), 4) with Approximate

/** Collection of exact counters */
lazy val exactCounters: Seq[Counter] = Seq(
Expand Down

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