[Support] Add LEB128 support to BinaryStreamReader/Writer.

Summary:
This patch adds support for ULEB128 and SLEB128 encoding and decoding to
BinaryStreamWriter and BinaryStreamReader respectively.

Support for ULEB128/SLEB128 will be used for eh-frame parsing in the JITLink
library currently under development (see https://reviews.llvm.org/D58704).

Reviewers: zturner, dblaikie

Subscribers: kristina, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60810

llvm-svn: 358584

1 files changed, 32 insertions, 1 deletions

diff --git a/llvm/lib/Support/BinaryStreamReader.cpp b/llvm/lib/Support/BinaryStreamReader.cpp
index 6f691bf..b177865 100644
--- a/llvm/lib/Support/BinaryStreamReader.cpp
+++ b/llvm/lib/Support/BinaryStreamReader.cpp
@@ -10,6 +10,7 @@
 
 #include "llvm/Support/BinaryStreamError.h"
 #include "llvm/Support/BinaryStreamRef.h"
+#include "llvm/Support/LEB128.h"
 
 using namespace llvm;
 using endianness = llvm::support::endianness;
@@ -40,6 +41,36 @@ Error BinaryStreamReader::readBytes(ArrayRef<uint8_t> &Buffer, uint32_t Size) {
   return Error::success();
 }
 
+Error BinaryStreamReader::readULEB128(uint64_t &Dest) {
+  SmallVector<uint8_t, 10> EncodedBytes;
+  ArrayRef<uint8_t> NextByte;
+
+  // Copy the encoded ULEB into the buffer.
+  do {
+    if (auto Err = readBytes(NextByte, 1))
+      return Err;
+    EncodedBytes.push_back(NextByte[0]);
+  } while (NextByte[0] & 0x80);
+
+  Dest = decodeULEB128(EncodedBytes.begin(), nullptr, EncodedBytes.end());
+  return Error::success();
+}
+
+Error BinaryStreamReader::readSLEB128(int64_t &Dest) {
+  SmallVector<uint8_t, 10> EncodedBytes;
+  ArrayRef<uint8_t> NextByte;
+
+  // Copy the encoded ULEB into the buffer.
+  do {
+    if (auto Err = readBytes(NextByte, 1))
+      return Err;
+    EncodedBytes.push_back(NextByte[0]);
+  } while (NextByte[0] & 0x80);
+
+  Dest = decodeSLEB128(EncodedBytes.begin(), nullptr, EncodedBytes.end());
+  return Error::success();
+}
+
 Error BinaryStreamReader::readCString(StringRef &Dest) {
   uint32_t OriginalOffset = getOffset();
   uint32_t FoundOffset = 0;
@@ -145,4 +176,4 @@ BinaryStreamReader::split(uint32_t Off) const {
   BinaryStreamReader W1{First};
   BinaryStreamReader W2{Second};
   return std::make_pair(W1, W2);
-}
\ No newline at end of file
+}