Check a quoted field for inner quotes with one vector compare

src/core.jl

@@ -526,6 +526,14 @@ function findcontent(buf::Vector{UInt8}, i::Int, j::Int,
     k = i + 1
     escaped = false
     if escape == closequote
+        # The common quoted field ends with its close quote and holds no other
+        # close quote: one 64-byte compare proves it for up to 63 content bytes.
+        n = j - i - 1
+        if 0 <= n <= 63 && i + 64 <= length(buf) && @inbounds(buf[j]) == closequote
+            m = GC.@preserve buf byte_mask_vec(pointer(buf, i + 1), closequote)
+            m & ((one(UInt64) << n) - one(UInt64)) == zero(UInt64) &&
+                return (i + 1, n, false, Parsers.RC_OK)
+        end
         GC.@preserve buf begin
             p = pointer(buf)
             @inbounds while k <= j

test/kernel.jl

@@ -741,6 +741,41 @@ end
 
 # ---------------------------------------------------------------------------
 
+@testset "quoted field content around the 64-byte check" begin
+    # A clean quoted field of up to 63 content bytes with 64 bytes of buffer
+    # after its start is decided by one vector compare; every other field takes
+    # the byte loop. Both must give the exact rule's answer.
+    q = UInt8('"')
+    function reference(buf, i, j)
+        k = i + 1
+        esc = false
+        while k <= j
+            if buf[k] == q
+                if k < j && buf[k + 1] == q
+                    esc = true
+                    k += 2
+                    continue
+                end
+                return (i + 1, j - i - 1, esc, k == j ? Parsers.RC_OK : Parsers.RC_INVALID)
+            end
+            k += 1
+        end
+        return (i + 1, j - i, esc, Parsers.RC_INVALID)
+    end
+    for n in (0, 1, 7, 8, 62, 63, 64, 65, 130), tail in (0, 1, 62, 63, 64, 65),
+        inner in (:none, :lone_first, :lone_last, :doubled_first, :doubled_last)
+        content = fill(UInt8('a'), n)
+        inner === :lone_first && n >= 1 && (content[1] = q)
+        inner === :lone_last && n >= 1 && (content[n] = q)
+        inner === :doubled_first && n >= 2 && (content[1:2] .= q)
+        inner === :doubled_last && n >= 2 && (content[n-1:n] .= q)
+        field = [q; content; q]
+        buf = [UInt8('x'); field; fill(UInt8('y'), tail)]
+        i, j = 2, 1 + length(field)
+        @test K.findcontent(buf, i, j, q, q, q) == reference(buf, i, j)
+    end
+end
+
 @testset "Parsers 3 integration" begin
     quotechar = UInt8('"')
     quoted = Vector{UInt8}(codeunits("\"a\"\"b\""))