Prepare wpiutil for merge into allwpilib.

wpiutil/src/main/native/cpp/support/leb128.cpp

@@ -0,0 +1,120 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2015-2018 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "support/leb128.h"
+
+#include "support/raw_istream.h"
+
+namespace wpi {
+
+/**
+ * Get size of unsigned LEB128 data
+ * @val: value
+ *
+ * Determine the number of bytes required to encode an unsigned LEB128 datum.
+ * The algorithm is taken from Appendix C of the DWARF 3 spec. For information
+ * on the encodings refer to section "7.6 - Variable Length Data". Return
+ * the number of bytes required.
+ */
+uint64_t SizeUleb128(uint64_t val) {
+  size_t count = 0;
+  do {
+    val >>= 7;
+    ++count;
+  } while (val != 0);
+  return count;
+}
+
+/**
+ * Write unsigned LEB128 data
+ * @addr: the address where the ULEB128 data is to be stored
+ * @val: value to be stored
+ *
+ * Encode an unsigned LEB128 encoded datum. The algorithm is taken
+ * from Appendix C of the DWARF 3 spec. For information on the
+ * encodings refer to section "7.6 - Variable Length Data". Return
+ * the number of bytes written.
+ */
+uint64_t WriteUleb128(llvm::SmallVectorImpl<char>& dest, uint64_t val) {
+  size_t count = 0;
+
+  do {
+    unsigned char byte = val & 0x7f;
+    val >>= 7;
+
+    if (val != 0)
+      byte |= 0x80;  // mark this byte to show that more bytes will follow
+
+    dest.push_back(byte);
+    count++;
+  } while (val != 0);
+
+  return count;
+}
+
+/**
+ * Read unsigned LEB128 data
+ * @addr: the address where the ULEB128 data is stored
+ * @ret: address to store the result
+ *
+ * Decode an unsigned LEB128 encoded datum. The algorithm is taken
+ * from Appendix C of the DWARF 3 spec. For information on the
+ * encodings refer to section "7.6 - Variable Length Data". Return
+ * the number of bytes read.
+ */
+uint64_t ReadUleb128(const char* addr, uint64_t* ret) {
+  uint32_t result = 0;
+  int shift = 0;
+  size_t count = 0;
+
+  while (1) {
+    unsigned char byte = *reinterpret_cast<const unsigned char*>(addr);
+    addr++;
+    count++;
+
+    result |= (byte & 0x7f) << shift;
+    shift += 7;
+
+    if (!(byte & 0x80)) break;
+  }
+
+  *ret = result;
+
+  return count;
+}
+
+/**
+ * Read unsigned LEB128 data from a stream
+ * @is: the input stream where the ULEB128 data is to be read from
+ * @ret: address to store the result
+ *
+ * Decode an unsigned LEB128 encoded datum. The algorithm is taken
+ * from Appendix C of the DWARF 3 spec. For information on the
+ * encodings refer to section "7.6 - Variable Length Data". Return
+ * false on stream error, true on success.
+ */
+bool ReadUleb128(raw_istream& is, uint64_t* ret) {
+  uint32_t result = 0;
+  int shift = 0;
+
+  while (1) {
+    unsigned char byte;
+    is.read(reinterpret_cast<char*>(&byte), 1);
+    if (is.has_error()) return false;
+
+    result |= (byte & 0x7f) << shift;
+    shift += 7;
+
+    if (!(byte & 0x80)) break;
+  }
+
+  *ret = result;
+
+  return true;
+}
+
+}  // namespace wpi