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      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)
     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.
     34 SourceLocation 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 
     60 void 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