Fix bounds errors when resampling with some arbitrary ratios (#539)

In some cases when `filt(::FIRFilter{FIRArbitrary}, x)` is called
with certain values of `x`, `filt!(buffer, ::FIRFilter{FIRArbitrary}, x)`
tries to write one sample too many to the buffer and a `BoundsError`
is thrown.  Add one extra sample to the buffer to catch these
exceptional cases.

(This code is really a hack and simply works around the deeper problem
of calculating the correct output buffer length; this should instead be
addressed properly in a future change.)

Closes #317.

src/Filters/stream_filt.jl

@@ -629,6 +629,19 @@ end
 
 function filt(self::FIRFilter{Tk}, x::AbstractVector{Tx}) where {Th,Tx,Tk<:FIRKernel{Th}}
     bufLen         = outputlength(self, length(x))
+    # In some cases when `filt(::FIRFilter{FIRArbitrary}, x)` is called
+    # with certain values of `x`, `filt!(buffer, ::FIRFilter{FIRArbitrary}, x)`
+    # tries to write one sample too many to the buffer and a `BoundsError`
+    # is thrown.  Add one extra sample to catch these exceptional cases.
+    #
+    # See https://github.com/JuliaDSP/DSP.jl/issues/317
+    #
+    # FIXME: Remove this if and when the code in
+    #        `filt!(buffer, ::FIRFilter{FIRArbitrary}, x)`
+    #        is updated to properly account for pathological arbitrary rates.
+    if Tk <: FIRArbitrary
+        bufLen += 1
+    end
     buffer         = Vector{promote_type(Th,Tx)}(undef, bufLen)
     samplesWritten = filt!(buffer, self, x)
 

test/resample.jl

@@ -97,6 +97,16 @@ end
     @test all(map(delta -> abs(delta) < 0.005, yDelta))
 end
 
+@testset "arbitrary ratio" begin
+    # https://github.com/JuliaDSP/DSP.jl/issues/317
+    @testset "Buffer length calculation" begin
+        @test length(resample(sin.(1:1:35546),  1/55.55)) == 641
+        @test length(resample(randn(1822), 0.9802414928649835)) == 1787
+        @test length(resample(1:16_367_000*2, 10_000_000/16_367_000)) == 20_000_001
+        @test resample(zeros(1000), 0.012) == zeros(13)
+    end
+end
+
 @testset "resample_filter" begin
     @testset "decimation" begin
         ratio = 1//2