From ad081e698a463ed943327ee6a4457f92e9434dd1 Mon Sep 17 00:00:00 2001
From: Bruno de Oliveira Abinader <bruno@mapbox.com>
Date: Thu, 30 Jun 2016 17:34:26 +0300
Subject: [core] Added CharArrayBuffer

Implements a custom std::streambuf to avoid creating temporary
std::string objects and thus optimizing image decode.

Suggested by @artemp in
https://github.com/mapbox/mapbox-gl-native/pull/5417#issuecomment-227700063.
---
 include/mbgl/util/char_array_buffer.hpp | 55 +++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 include/mbgl/util/char_array_buffer.hpp

(limited to 'include/mbgl/util')

diff --git a/include/mbgl/util/char_array_buffer.hpp b/include/mbgl/util/char_array_buffer.hpp
new file mode 100644
index 0000000000..177f005477
--- /dev/null
+++ b/include/mbgl/util/char_array_buffer.hpp
@@ -0,0 +1,55 @@
+#pragma once
+
+#include <streambuf>
+
+namespace mbgl {
+namespace util {
+
+// ref https://artofcode.wordpress.com/2010/12/12/deriving-from-stdstreambuf/
+
+class CharArrayBuffer : public std::streambuf
+{
+public:
+    CharArrayBuffer(char const* data, std::size_t size)
+        : begin_(data), end_(data + size), current_(data) {}
+
+private:
+    int_type underflow() final {
+        if (current_ == end_) {
+            return traits_type::eof();
+        }
+        return traits_type::to_int_type(*current_);
+    }
+
+    int_type uflow() final {
+        if (current_ == end_) {
+            return traits_type::eof();
+        }
+        return traits_type::to_int_type(*current_++);
+    }
+
+    int_type pbackfail(int_type ch) final {
+        if (current_ == begin_ || (ch != traits_type::eof() && ch != current_[-1])) {
+            return traits_type::eof();
+        }
+        return traits_type::to_int_type(*--current_);
+    }
+
+    std::streamsize showmanyc() final {
+        return end_ - current_;
+    }
+
+    pos_type seekoff(off_type off, std::ios_base::seekdir dir, std::ios_base::openmode) final {
+        if (dir == std::ios_base::beg) current_ = std::min(begin_ + off, end_);
+        else if (dir == std::ios_base::cur) current_ = std::min(current_ + off, end_);
+        else current_ = std::max(end_ - off, begin_); // dir == std::ios_base::end
+        return pos_type(off_type(current_ - begin_));
+    }
+
+    char const * const begin_;
+    char const * const end_;
+    char const * current_;
+};
+
+} // namespace util
+} // namespace mbgl
-- 
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