112 lines
3.9 KiB
C++
112 lines
3.9 KiB
C++
#ifndef UTIL_FAKE_OSTREAM_H
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#define UTIL_FAKE_OSTREAM_H
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#include "util/float_to_string.hh"
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#include "util/integer_to_string.hh"
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#include "util/string_piece.hh"
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#include <cassert>
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#include <limits>
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#include <stdint.h>
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namespace util {
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/* Like std::ostream but without being incredibly slow.
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* Supports most of the built-in types except for long double.
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*
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* The FakeOStream class is intended to be inherited from. The inherting class
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* should provide:
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* public:
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* Derived &flush();
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* Derived &write(const void *data, std::size_t length);
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*
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* private: or protected:
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* friend class FakeOStream;
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* char *Ensure(std::size_t amount);
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* void AdvanceTo(char *to);
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*
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* The Ensure function makes enough space for an in-place write and returns
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* where to write. The AdvanceTo function happens after the write, saying how
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* much was actually written.
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*
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* Precondition:
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* amount <= kToStringMaxBytes for in-place writes.
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*/
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template <class Derived> class FakeOStream {
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public:
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FakeOStream() {}
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// This also covers std::string and char*
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Derived &operator<<(StringPiece str) {
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return C().write(str.data(), str.size());
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}
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// Handle integers by size and signedness.
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private:
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template <class Arg> struct EnableIfKludge {
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typedef Derived type;
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};
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template <class From, unsigned Length = sizeof(From), bool Signed = std::numeric_limits<From>::is_signed, bool IsInteger = std::numeric_limits<From>::is_integer> struct Coerce {};
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template <class From> struct Coerce<From, 2, false, true> { typedef uint16_t To; };
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template <class From> struct Coerce<From, 4, false, true> { typedef uint32_t To; };
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template <class From> struct Coerce<From, 8, false, true> { typedef uint64_t To; };
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template <class From> struct Coerce<From, 2, true, true> { typedef int16_t To; };
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template <class From> struct Coerce<From, 4, true, true> { typedef int32_t To; };
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template <class From> struct Coerce<From, 8, true, true> { typedef int64_t To; };
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public:
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template <class From> typename EnableIfKludge<typename Coerce<From>::To>::type &operator<<(const From value) {
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return CallToString(static_cast<typename Coerce<From>::To>(value));
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}
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// Character types that get copied as bytes instead of displayed as integers.
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Derived &operator<<(char val) { return put(val); }
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Derived &operator<<(signed char val) { return put(static_cast<char>(val)); }
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Derived &operator<<(unsigned char val) { return put(static_cast<char>(val)); }
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Derived &operator<<(bool val) { return put(val + '0'); }
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// enums will fall back to int but are not caught by the template.
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Derived &operator<<(int val) { return CallToString(static_cast<typename Coerce<int>::To>(val)); }
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Derived &operator<<(float val) { return CallToString(val); }
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Derived &operator<<(double val) { return CallToString(val); }
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// This is here to catch all the other pointer types.
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Derived &operator<<(const void *value) { return CallToString(value); }
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// This is here because the above line also catches const char*.
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Derived &operator<<(const char *value) { return *this << StringPiece(value); }
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Derived &operator<<(char *value) { return *this << StringPiece(value); }
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Derived &put(char val) {
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char *c = C().Ensure(1);
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*c = val;
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C().AdvanceTo(++c);
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return C();
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}
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char widen(char val) const { return val; }
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private:
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// References to derived class for convenience.
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Derived &C() {
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return *static_cast<Derived*>(this);
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}
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const Derived &C() const {
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return *static_cast<const Derived*>(this);
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}
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// This is separate to prevent an infinite loop if the compiler considers
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// types the same (i.e. gcc std::size_t and uint64_t or uint32_t).
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template <class T> Derived &CallToString(const T value) {
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C().AdvanceTo(ToString(value, C().Ensure(ToStringBuf<T>::kBytes)));
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return C();
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}
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};
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} // namespace
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#endif // UTIL_FAKE_OSTREAM_H
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