specialized ZAM operators for speeding up cat() operations

src/script_opt/ZAM/BuiltInSupport.h

@@ -0,0 +1,119 @@
+// See the file "COPYING" in the main distribution directory for copyright.
+
+#include "zeek/Desc.h"
+#include "zeek/Expr.h"
+
+namespace zeek::detail
+	{
+
+// Base class for tracking information about a single cat() argument, with
+// optimizations for some common cases.
+class CatArg
+	{
+public:
+	CatArg(std::string _s) : s(std::move(_s)) { max_size = s->size(); }
+
+	virtual ~CatArg() { }
+
+	size_t MaxSize(ZVal* zframe, int slot)
+		{
+		return max_size ? *max_size : ComputeMaxSize(zframe, slot);
+		}
+
+	virtual void RenderInto(ZVal* zframe, int slot, char*& res)
+		{
+		auto n = *max_size;
+		memcpy(res, s->data(), n);
+		res += n;
+		}
+
+protected:
+	CatArg() { }
+	CatArg(size_t _max_size) : max_size(_max_size) { }
+
+	virtual size_t ComputeMaxSize(ZVal* zframe, int slot) { return 0; }
+
+	// Present if max size is known a priori.
+	std::optional<size_t> max_size;
+
+	// Present if the argument is a constant.
+	std::optional<std::string> s;
+	};
+
+class FixedCatArg : public CatArg
+	{
+public:
+	FixedCatArg(const TypePtr& t);
+
+	void RenderInto(ZVal* zframe, int slot, char*& res) override;
+
+protected:
+	const TypePtr& t;
+	char tmp[256];
+	};
+
+class StringCatArg : public CatArg
+	{
+public:
+	StringCatArg() : CatArg() { }
+
+	void RenderInto(ZVal* zframe, int slot, char*& res) override
+		{
+		auto s = zframe[slot].AsString();
+		auto n = s->Len();
+		memcpy(res, s->Bytes(), n);
+		res += n;
+		}
+
+protected:
+	size_t ComputeMaxSize(ZVal* zframe, int slot) override
+		{
+		return zframe[slot].AsString()->Len();
+		}
+	};
+
+class PatternCatArg : public CatArg
+	{
+public:
+	PatternCatArg() : CatArg() { }
+
+	void RenderInto(ZVal* zframe, int slot, char*& res) override
+		{
+		*(res++) = '/';
+		strcpy(res, text);
+		res += n;
+		*(res++) = '/';
+		}
+
+protected:
+	size_t ComputeMaxSize(ZVal* zframe, int slot) override;
+
+	const char* text;
+	size_t n = 0;
+	};
+
+class DescCatArg : public CatArg
+	{
+public:
+	DescCatArg(const TypePtr& _t) : CatArg(), t(_t) { d.SetStyle(RAW_STYLE); }
+
+	void RenderInto(ZVal* zframe, int slot, char*& res) override
+		{
+		auto n = d.Len();
+		memcpy(res, d.Bytes(), n);
+		res += n;
+		d.Clear();
+		}
+
+protected:
+	size_t ComputeMaxSize(ZVal* zframe, int slot) override
+		{
+		zframe[slot].ToVal(t)->Describe(&d);
+		return d.Len();
+		}
+
+	ODesc d;
+	TypePtr t;
+	};
+
+	} // namespace zeek::detail