lib/Lex/ScratchBuffer.cpp

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