src/compiler/translator/ImmutableStringBuilder.h

//
// Copyright 2018 The ANGLE Project Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// ImmutableStringBuilder.h: Stringstream-like utility for building pool allocated strings where the
// maximum length is known in advance.
//

#ifndef COMPILER_TRANSLATOR_IMMUTABLESTRINGBUILDER_H_
#define COMPILER_TRANSLATOR_IMMUTABLESTRINGBUILDER_H_

#include <cstring>

#include "compiler/translator/ImmutableString.h"

namespace sh
{

class ImmutableStringBuilder
{
  public:
    ImmutableStringBuilder(size_t maxLength)
        : mPos(0u), mMaxLength(maxLength), mData(AllocateEmptyPoolCharArray(maxLength))
    {}

    ImmutableStringBuilder &operator<<(const ImmutableString &str);
    ImmutableStringBuilder &operator<<(const char *str) { return *this << ImmutableString(str); }
    ImmutableStringBuilder &operator<<(char c);
    ImmutableStringBuilder &operator<<(int i) { return *this << static_cast<int64_t>(i); }
    ImmutableStringBuilder &operator<<(unsigned i) { return *this << static_cast<uint64_t>(i); }
    ImmutableStringBuilder &operator<<(int64_t i);
    ImmutableStringBuilder &operator<<(uint64_t i);

    // This invalidates the ImmutableStringBuilder, so it should only be called once.
    operator ImmutableString();

    template <typename T>
    void appendHex(T number)
    {
        ASSERT(mData != nullptr);
        ASSERT(mPos + sizeof(T) * 2u <= mMaxLength);
        int index = static_cast<int>(sizeof(T)) * 2 - 1;
        // Loop through leading zeroes.
        while (((number >> (index * 4)) & 0xfu) == 0 && index > 0)
        {
            --index;
        }
        // Write the rest of the hex digits.
        while (index >= 0)
        {
            char digit     = static_cast<char>((number >> (index * 4)) & 0xfu);
            char digitChar = (digit < 10) ? (digit + '0') : (digit + ('a' - 10));
            mData[mPos++]  = digitChar;
            --index;
        }
    }

    template <typename T>
    static constexpr size_t GetHexCharCount()
    {
        return sizeof(T) * 2;
    }

  private:
    inline static char *AllocateEmptyPoolCharArray(size_t strLength)
    {
        size_t requiredSize = strLength + 1u;
        return static_cast<char *>(GetGlobalPoolAllocator()->allocate(requiredSize));
    }

    size_t mPos;
    size_t mMaxLength;
    char *mData;
};

// GLSL ES 3.00.6 section 3.9: the maximum length of an identifier is 1024 characters.
constexpr unsigned int kESSLMaxIdentifierLength = 1024u;

namespace impl
{

constexpr inline size_t GetCharCount(uint64_t x)
{
    size_t digits = 1;
    uint64_t max  = 10;
    for (; digits < 19; ++digits)
    {
        if (x < max)
            break;
        max *= 10;
    }
    return digits;
}

constexpr inline size_t GetCharCount(int64_t x)
{
    if (x == INT64_MIN)
    {
        return 19 + 1;
    }
    if (x < 0)
    {
        return GetCharCount(static_cast<uint64_t>(-x)) + 1;
    }
    return GetCharCount(static_cast<uint64_t>(x));
}

constexpr inline size_t GetCharCount(int x)
{
    return GetCharCount(static_cast<int64_t>(x));
}

constexpr inline size_t GetCharCount(unsigned x)
{
    return GetCharCount(static_cast<int64_t>(x));
}

constexpr inline size_t GetCharCount(const ImmutableString &str)
{
    return str.length();
}

constexpr inline size_t GetCharCount(const char *str)
{
    return angle::ConstStrLen(str);
}

constexpr inline size_t GetCharCount(char)
{
    return 1;
}

}  // namespace impl

template <typename... Args>
ImmutableString BuildConcatenatedImmutableString(Args... args)
{
    ImmutableStringBuilder builder((impl::GetCharCount(args) + ...));
    (builder << ... << args);
    return builder;
}

}  // namespace sh

#endif  // COMPILER_TRANSLATOR_IMMUTABLESTRINGBUILDER_H_