From f1e9c36f004febb4d983b37acd0c8c34a3fd5101 Mon Sep 17 00:00:00 2001
From: gibbed <rick@gibbed.us>
Date: Fri, 19 Jun 2015 09:50:54 -0500
Subject: [PATCH] Better ringbuffer implementation.

---
 src/xenia/base/ring_buffer.cc | 88 +++++++++++++++++++----------------
 src/xenia/base/ring_buffer.h  | 33 ++++++++++---
 2 files changed, 74 insertions(+), 47 deletions(-)

diff --git a/src/xenia/base/ring_buffer.cc b/src/xenia/base/ring_buffer.cc
index 7d9de5289..45225325b 100644
--- a/src/xenia/base/ring_buffer.cc
+++ b/src/xenia/base/ring_buffer.cc
@@ -9,59 +9,65 @@
 
 #include "xenia/base/ring_buffer.h"
 
+#include <algorithm>
 #include <cstring>
 
 namespace xe {
 
-RingBuffer::RingBuffer(uint8_t *raw_buffer, size_t size, size_t write_offset)
-    : raw_buffer_(raw_buffer),
-      size_(size),
-      write_offset_(write_offset) {}
+RingBuffer::RingBuffer(uint8_t* raw_buffer, size_t size, size_t read_offset, size_t write_offset)
+    : raw_buffer_(raw_buffer)
+    , size_(size)
+    , read_offset_(read_offset)
+    , write_offset_(write_offset) {}
 
-size_t RingBuffer::Write(uint8_t *buffer, size_t num_bytes) {
-  size_t bytes_written = 0;
-  size_t input_offset = 0;
-  size_t bytes_to_write = 0;
-
-  // write offset -> end
-  bytes_to_write =
-        num_bytes < size_ - write_offset_ ? num_bytes : size_ - write_offset_;
-
-  std::memcpy(raw_buffer_ + write_offset_, buffer, bytes_to_write);
-  input_offset = bytes_to_write;
-  write_offset_ += bytes_to_write;
-
-  bytes_written += bytes_to_write;
-
-  // Wraparound (begin -> num_bytes)
-  if (input_offset < num_bytes) {
-    bytes_to_write = num_bytes - input_offset;
-
-    std::memcpy(raw_buffer_, buffer + input_offset, bytes_to_write);
-    write_offset_ = bytes_to_write;
-
-    bytes_written += bytes_to_write;
+size_t RingBuffer::Skip(size_t num_bytes) {
+  num_bytes = std::min(read_size(), num_bytes);
+  if (read_offset_ + num_bytes < size_) {
+    read_offset_ += num_bytes;
+  } else {
+    read_offset_ = num_bytes - (size_ - read_offset_);
   }
-
-  return bytes_written;
+  return num_bytes;
 }
 
-size_t RingBuffer::DistanceToOffset(size_t offset) {
-  // Make sure the offset is in range.
-  if (offset > size_) {
-    offset %= size_;
+size_t RingBuffer::Read(uint8_t* buffer, size_t num_bytes) {
+  num_bytes = std::min(read_size(), num_bytes);
+  if (!num_bytes) {
+    return 0;
   }
 
-  if (offset < size_ && offset >= write_offset_) {
-    // Doesn't wraparound.
-    return offset - write_offset_;
+  if (read_offset_ + num_bytes < size_) {
+    std::memcpy(buffer, raw_buffer_ + read_offset_, num_bytes);
+    read_offset_ += num_bytes;
   } else {
-    // Wraparound.
-    size_t dist = size_ - write_offset_;
-    dist += offset;
-
-    return dist;
+    size_t left_half = size_ - read_offset_;
+    size_t right_half = size_ - left_half;
+    std::memcpy(buffer, raw_buffer_ + read_offset_, left_half);
+    std::memcpy(buffer + left_half, raw_buffer_, right_half);
+    read_offset_ = right_half;
   }
+
+  return num_bytes;
+}
+
+size_t RingBuffer::Write(uint8_t* buffer, size_t num_bytes) {
+  num_bytes = std::min(num_bytes, write_size());
+  if (!num_bytes) {
+    return 0;
+  }
+
+  if (write_offset_ + num_bytes < size_) {
+    std::memcpy(raw_buffer_ + write_offset_, buffer, num_bytes);
+    write_offset_ += num_bytes;
+  } else {
+    size_t left_half = size_ - write_offset_;
+    size_t right_half = size_ - left_half;
+    std::memcpy(raw_buffer_ + write_offset_, buffer, left_half);
+    std::memcpy(raw_buffer_, buffer + left_half, right_half);
+    write_offset_ = right_half;
+  }
+
+  return num_bytes;
 }
 
 } // namespace xe
diff --git a/src/xenia/base/ring_buffer.h b/src/xenia/base/ring_buffer.h
index 50c3e52f1..4d3830195 100644
--- a/src/xenia/base/ring_buffer.h
+++ b/src/xenia/base/ring_buffer.h
@@ -18,18 +18,39 @@ namespace xe {
 
 class RingBuffer {
   public:
-    RingBuffer(uint8_t *raw_buffer, size_t size, size_t write_offset = 0);
+    RingBuffer(uint8_t* raw_buffer, size_t size, size_t read_offset, size_t write_offset);
 
-    size_t Write(uint8_t *buffer, size_t num_bytes);
+    size_t Read(uint8_t* buffer, size_t num_bytes);
+    size_t Skip(size_t num_bytes);
+    size_t Write(uint8_t* buffer, size_t num_bytes);
 
-    size_t DistanceToOffset(size_t offset);
-
-    void set_write_offset(size_t write_offset) { write_offset_ = write_offset; }
+    size_t read_offset() { return read_offset_; }
     size_t write_offset() { return write_offset_; }
 
+    size_t read_size() {
+      if (read_offset_ == write_offset_) {
+        return 0;
+      }
+      if (read_offset_ < write_offset_) {
+        return write_offset_ - read_offset_;
+      }
+      return (size_ - read_offset_) + write_offset_;
+    }
+
+    size_t write_size() {
+      if (write_offset_ == read_offset_) {
+        return size_;
+      }
+      if (write_offset_ < read_offset_) {
+        return read_offset_ - write_offset_;
+      }
+      return (size_ - write_offset_) + read_offset_;
+    }
+
   private:
-    uint8_t *raw_buffer_;
+    uint8_t* raw_buffer_;
     size_t size_;
+    size_t read_offset_;
     size_t write_offset_;
 };