test for gaussian_bitblast_sample

src/dist/number/fix.jl

@@ -688,6 +688,7 @@ A modified version of the function bitblast that works with the assumption of lo
 function bitblast_sample(::Type{DistFix{W,F}}, dist::ContinuousUnivariateDistribution, 
     numpieces::Int, start::Float64, stop::Float64, offset::Float64, width::Float64) where {W,F}
 
+    @show start, stop, numpieces, offset, width
     # count bits and pieces
     @assert -(2^(W-F-1)) <= start < stop <= 2^(W-F-1)
     f_range_bits = log2((stop - start)*2^F)
@@ -710,6 +711,8 @@ function bitblast_sample(::Type{DistFix{W,F}}, dist::ContinuousUnivariateDistrib
         piece_probs[i] = 0
         # Warning: A potential source of high runtime
         for j=1:intervals_per_piece
+            @show firstinter + offset + width + (j-1)/2^F
+            @show firstinter + offset + (j-1)/2^F
             piece_probs[i] += cdf(dist, firstinter + offset + width + (j-1)/2^F) - cdf(dist, firstinter + offset + (j-1)/2^F)
         end
         total_prob += piece_probs[i]
@@ -719,6 +722,10 @@ function bitblast_sample(::Type{DistFix{W,F}}, dist::ContinuousUnivariateDistrib
         linear_piece_probs[i] = (border_probs[i][1] + border_probs[i][2])/2 * 2^(bits_per_piece)
     end
 
+
+    @show piece_probs
+    @show total_prob
+
     PieceChoice = DistUInt{max(1,Int(log2(numpieces)))}
     piecechoice = discrete(PieceChoice, piece_probs ./ total_prob) # selector variable for pieces
     slope_flips = Vector(undef, numpieces)

src/util.jl

@@ -131,16 +131,16 @@ The functions takes as input lower order bits for a gaussian distribution and re
 """
 function gaussian_bitblast_sample(::Type{DistFix{W, F}}, mean::Float64, std::Float64, numpieces::Int64, start::Float64, stop::Float64, lsb::Vector{Bool}) where {W, F}
     distribution = Normal(mean, std)
-    nbits = length(lsbs)
+    nbits = length(lsb)
     DFiP = DistFix{W-nbits, F-nbits}
     width = 1/2^F
     offset = 0.0
     for i in 1:nbits
-        if lsbs[i]
-            offset += 2^(F-nbits+i)
+        if lsb[i]
+            offset += 1/2^(F-nbits+i)
         end
     end
 
     sub_gaussian = bitblast_sample(DFiP, distribution, numpieces, start, stop, offset, width)
-    DistFix{W, F}([sub_gaussian.mantissa.number.bits..., lsbs...])
+    DistFix{W, F}([sub_gaussian.mantissa.number.bits..., lsb...])
 end

test/util_test.jl

@@ -104,3 +104,17 @@ end
         └── Leaf
         """
 end
+
+# TODO: test for negative F
+@testset "gaussian_bitblast_sample" begin
+    x1 = gaussian_bitblast_sample(DistFix{3, 1}, 0.0, 1.0, 2, -1.0, 1.0, [false])
+    x2 = gaussian_bitblast_sample(DistFix{3, 1}, 0.0, 1.0, 2, -1.0, 1.0, [true])
+    x = ifelse(flip(0.5), x1, x2)
+    p1 = pr(x)
+
+    y = bitblast(DistFix{3, 1}, Normal(0, 1), 4, -1.0, 1.0)
+    p2 = pr(y)
+    for i in keys(p1)
+        @test p1[i] ≈ p2[i]
+    end
+end