Fix findnext on BitArrays

Author: kmsquire

base/bitarray.jl

@@ -1449,7 +1449,16 @@ end
 # returns the index of the next non-zero element, or 0 if all zeros
 function findnext(B::BitArray, start::Integer)
     Bc = B.chunks
-    for i = div(start-1,64)+1:length(Bc)
+
+    chunk_start = div(start-1, 64)+1
+    within_chunk_start = start-1-chunk_start*64
+    mask = _msk64-((1<<within_chunk_start)-1)
+
+    if Bc[chunk_start] & mask != 0
+        return (chunk_start-1) << 6 + trailing_zeros(Bc[chunk_start] & mask) + 1
+    end
+
+    for i = chunk_start+1:length(Bc)
         if Bc[i] != 0
             return (i-1) << 6 + trailing_zeros(Bc[i]) + 1
         end
@@ -1465,7 +1474,16 @@ function findnextnot(B::BitArray, start::Integer)
     if l == 0
         return 0
     end
-    for i = div(start-1,64)+1:l-1
+
+    chunk_start = div(start-1, 64)+1
+    within_chunk_start = start-1-chunk_start*64
+    mask = (1<<within_chunk_start)-1
+
+    if Bc[chunk_start] | mask != _msk64
+        return (chunk_start-1) << 6 + trailing_ones(Bc[chunk_start] | mask) + 1
+    end
+
+    for i = chunk_start+1:l-1
         if Bc[i] != _msk64
             return (i-1) << 6 + trailing_ones(Bc[i]) + 1
         end

test/bitarray.jl

@@ -521,6 +521,20 @@ b1 = randbool(v1)
 
 @check_bit_operation find Vector{Int} (b1,)
 
+b1 = trues(v1)
+for i = 0:v1-1
+    @test findfirst(b1 >> i) == i+1
+    @test Base.findfirstnot(~(b1 >> i)) == i+1
+end
+
+for i = 3:v1-1
+    for j = 2:i
+        submask = b1 << (v1-j+1)
+        @test findnext((b1 >> i) | submask,j) == i+1
+        @test Base.findnextnot((~(b1 >> i)) $ submask,j) == i+1
+    end
+end
+
 b1 = randbool(n1, n2)
 @check_bit_operation findn_nzs (Vector{Int}, Vector{Int}, BitArray) (b1,)