riscv/rocket-chip
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Added popcount util

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Henry Cook 2012-02-24 16:25:36 -08:00
parent a1600d95db
commit 4fa31b300b
1 changed files with 35 additions and 0 deletions
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35
rocket/src/main/scala/util.scala
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@ -32,6 +32,41 @@ object FillInterleaved
}
}
// http://aggregate.ee.engr.uky.edu/MAGIC/#Population%20Count%20%28Ones%20Count%29
// http://bits.stephan-brumme.com/countBits.html
object PopCount
{
def apply(in: Bits) =
{
require(in.width <= 32)
val w = log2up(in.width+1)
var x = in
if(in.width == 2) {
x = x - ((x >> UFix(1)) & Bits("h_5555_5555"))
} else if(in.width <= 4) {
x = x - ((x >> UFix(1)) & Bits("h_5555_5555"))
x = (((x >> UFix(2)) & Bits("h_3333_3333")) + (x & Bits("h_3333_3333")))
} else if(in.width <= 8) {
x = x - ((x >> UFix(1)) & Bits("h_5555_5555"))
x = (((x >> UFix(2)) & Bits("h_3333_3333")) + (x & Bits("h_3333_3333")))
x = ((x >> UFix(4)) + x)
} else {
// count bits of each 2-bit chunk
x = x - ((x >> UFix(1)) & Bits("h_5555_5555"))
// count bits of each 4-bit chunk
x = (((x >> UFix(2)) & Bits("h_3333_3333")) + (x & Bits("h_3333_3333")))
// count bits of each 8-bit chunk
x = ((x >> UFix(4)) + x)
// mask junk in upper bits
x = x & Bits("h_0f0f_0f0f")
// add all four 8-bit chunks
x = x + (x >> UFix(8))
x = x + (x >> UFix(16))
}
x(w-1,0)
}
}
object Reverse
{
def apply(in: Bits) =