1//===--- ScratchBuffer.cpp - Scratch space for forming tokens -------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10//  This file implements the ScratchBuffer interface.
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/Lex/ScratchBuffer.h"
15#include "clang/Basic/SourceManager.h"
16#include "llvm/Support/MemoryBuffer.h"
17#include <cstring>
18using namespace clang;
19
20// ScratchBufSize - The size of each chunk of scratch memory.  Slightly less
21//than a page, almost certainly enough for anything. :)
22static const unsigned ScratchBufSize = 4060;
23
24ScratchBuffer::ScratchBuffer(SourceManager &SM)
25    : SourceMgr(SM), CurBuffer(nullptr) {
26  // Set BytesUsed so that the first call to getToken will require an alloc.
27  BytesUsed = ScratchBufSize;
28}
29
30/// getToken - Splat the specified text into a temporary MemoryBuffer and
31/// return a SourceLocation that refers to the token.  This is just like the
32/// method below, but returns a location that indicates the physloc of the
33/// token.
34SourceLocation ScratchBuffer::getToken(const char *Buf, unsigned Len,
35                                       const char *&DestPtr) {
36  if (BytesUsed+Len+2 > ScratchBufSize)
37    AllocScratchBuffer(Len+2);
38
39  // Prefix the token with a \n, so that it looks like it is the first thing on
40  // its own virtual line in caret diagnostics.
41  CurBuffer[BytesUsed++] = '\n';
42
43  // Return a pointer to the character data.
44  DestPtr = CurBuffer+BytesUsed;
45
46  // Copy the token data into the buffer.
47  memcpy(CurBuffer+BytesUsed, Buf, Len);
48
49  // Remember that we used these bytes.
50  BytesUsed += Len+1;
51
52  // Add a NUL terminator to the token.  This keeps the tokens separated, in
53  // case they get relexed, and puts them on their own virtual lines in case a
54  // diagnostic points to one.
55  CurBuffer[BytesUsed-1] = '\0';
56
57  return BufferStartLoc.getLocWithOffset(BytesUsed-Len-1);
58}
59
60void ScratchBuffer::AllocScratchBuffer(unsigned RequestLen) {
61  // Only pay attention to the requested length if it is larger than our default
62  // page size.  If it is, we allocate an entire chunk for it.  This is to
63  // support gigantic tokens, which almost certainly won't happen. :)
64  if (RequestLen < ScratchBufSize)
65    RequestLen = ScratchBufSize;
66
67  llvm::MemoryBuffer *Buf =
68    llvm::MemoryBuffer::getNewMemBuffer(RequestLen, "<scratch space>");
69  FileID FID = SourceMgr.createFileID(Buf);
70  BufferStartLoc = SourceMgr.getLocForStartOfFile(FID);
71  CurBuffer = const_cast<char*>(Buf->getBufferStart());
72  BytesUsed = 1;
73  CurBuffer[0] = '0';  // Start out with a \0 for cleanliness.
74}
75