Reorganize CLZWDecoder.

- Add a ctor and initialize more variables there, or initialize them in
  the class declaration instead of in Decode().
- Take in the source data as a span instead of a raw pointer.
- Change |m_Early| to |m_nEarly| and avoid adding ints with bools.
- Fix nits and lint errors.

Change-Id: I1b95619c2e094796f9e7a9dfea07ad55cacbc1da
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/56412
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

core/fxcodec/flate/flatemodule.cpp

diff --git a/core/fxcodec/flate/flatemodule.cpp b/core/fxcodec/flate/flatemodule.cpp
index 3604efb..0809c5b 100644
--- a/core/fxcodec/flate/flatemodule.cpp
+++ b/core/fxcodec/flate/flatemodule.cpp
@@ -108,73 +108,66 @@
 
 class CLZWDecoder {
  public:
-  bool Decode(uint8_t* dest_buf,
-              uint32_t* dest_size,
-              const uint8_t* src_buf,
-              uint32_t* src_size,
-              bool early_change);
+  CLZWDecoder(pdfium::span<const uint8_t> src_span, bool early_change);
+
+  bool Decode(uint8_t* dest_buf, uint32_t* dest_size, uint32_t* src_size);
 
  private:
   void AddCode(uint32_t prefix_code, uint8_t append_char);
   void DecodeString(uint32_t code);
 
-  uint32_t m_InPos;
-  uint32_t m_OutPos;
+  pdfium::span<const uint8_t> const m_spSrc;
+  uint32_t m_InPos = 0;
+  uint32_t m_OutPos = 0;
   uint8_t* m_pOutput;
-  const uint8_t* m_pInput;
-  bool m_Early;
-  uint32_t m_nCodes;
+  const uint8_t m_nEarly;
+  uint32_t m_nCodes = 0;
   uint32_t m_StackLen;
-  int m_CodeLen;
+  uint8_t m_CodeLen = 9;
   uint32_t m_CodeArray[5021];
   uint8_t m_DecodeStack[4000];
 };
 
+CLZWDecoder::CLZWDecoder(pdfium::span<const uint8_t> src_span,
+                         bool early_change)
+    : m_spSrc(src_span), m_nEarly(early_change ? 1 : 0) {}
+
 void CLZWDecoder::AddCode(uint32_t prefix_code, uint8_t append_char) {
-  if (m_nCodes + m_Early == 4094) {
+  if (m_nCodes + m_nEarly == 4094)
     return;
-  }
+
   m_CodeArray[m_nCodes++] = (prefix_code << 16) | append_char;
-  if (m_nCodes + m_Early == 512 - 258) {
+  if (m_nCodes + m_nEarly == 512 - 258)
     m_CodeLen = 10;
-  } else if (m_nCodes + m_Early == 1024 - 258) {
+  else if (m_nCodes + m_nEarly == 1024 - 258)
     m_CodeLen = 11;
-  } else if (m_nCodes + m_Early == 2048 - 258) {
+  else if (m_nCodes + m_nEarly == 2048 - 258)
     m_CodeLen = 12;
-  }
 }
 
 void CLZWDecoder::DecodeString(uint32_t code) {
   while (1) {
     int index = code - 258;
-    if (index < 0 || index >= (int)m_nCodes) {
+    if (index < 0 || static_cast<uint32_t>(index) >= m_nCodes)
       break;
-    }
+
     uint32_t data = m_CodeArray[index];
-    if (m_StackLen >= sizeof(m_DecodeStack)) {
+    if (m_StackLen >= sizeof(m_DecodeStack))
       return;
-    }
-    m_DecodeStack[m_StackLen++] = (uint8_t)data;
+
+    m_DecodeStack[m_StackLen++] = static_cast<uint8_t>(data);
     code = data >> 16;
   }
-  if (m_StackLen >= sizeof(m_DecodeStack)) {
+  if (m_StackLen >= sizeof(m_DecodeStack))
     return;
-  }
-  m_DecodeStack[m_StackLen++] = (uint8_t)code;
+
+  m_DecodeStack[m_StackLen++] = static_cast<uint8_t>(code);
 }
 
 bool CLZWDecoder::Decode(uint8_t* dest_buf,
                          uint32_t* dest_size,
-                         const uint8_t* src_buf,
-                         uint32_t* src_size,
-                         bool early_change) {
-  m_CodeLen = 9;
-  m_InPos = 0;
-  m_OutPos = 0;
-  m_pInput = src_buf;
+                         uint32_t* src_size) {
   m_pOutput = dest_buf;
-  m_Early = early_change;
-  m_nCodes = 0;
   uint32_t old_code = 0xFFFFFFFF;
   uint8_t last_char = 0;
   while (1) {
@@ -182,19 +175,20 @@
       break;
 
     int byte_pos = m_InPos / 8;
-    int bit_pos = m_InPos % 8, bit_left = m_CodeLen;
+    int bit_pos = m_InPos % 8;
+    uint8_t bit_left = m_CodeLen;
     uint32_t code = 0;
     if (bit_pos) {
       bit_left -= 8 - bit_pos;
-      code = (m_pInput[byte_pos++] & ((1 << (8 - bit_pos)) - 1)) << bit_left;
+      code = (m_spSrc[byte_pos++] & ((1 << (8 - bit_pos)) - 1)) << bit_left;
     }
     if (bit_left < 8) {
-      code |= m_pInput[byte_pos] >> (8 - bit_left);
+      code |= m_spSrc[byte_pos] >> (8 - bit_left);
     } else {
       bit_left -= 8;
-      code |= m_pInput[byte_pos++] << bit_left;
+      code |= m_spSrc[byte_pos++] << bit_left;
       if (bit_left)
-        code |= m_pInput[byte_pos] >> (8 - bit_left);
+        code |= m_spSrc[byte_pos] >> (8 - bit_left);
     }
     m_InPos += m_CodeLen;
 
@@ -795,20 +789,18 @@
   PredictorType predictor_type = GetPredictor(predictor);
 
   if (bLZW) {
-    auto decoder = pdfium::MakeUnique<CLZWDecoder>();
+    auto decoder = pdfium::MakeUnique<CLZWDecoder>(src_span, bEarlyChange);
     *dest_size = 0xFFFFFFFF;
     offset = src_span.size();
-    bool success = decoder->Decode(nullptr, dest_size, src_span.data(), &offset,
-                                   bEarlyChange);
+    bool success = decoder->Decode(nullptr, dest_size, &offset);
     if (!success || *dest_size == 0 || *dest_size + 1 < *dest_size)
       return FX_INVALID_OFFSET;
 
-    decoder = pdfium::MakeUnique<CLZWDecoder>();
+    decoder = pdfium::MakeUnique<CLZWDecoder>(src_span, bEarlyChange);
     dest_buf->reset(FX_Alloc(uint8_t, *dest_size + 1));
     uint8_t* dest_buf_ptr = dest_buf->get();
     dest_buf_ptr[*dest_size] = '\0';
-    decoder->Decode(dest_buf_ptr, dest_size, src_span.data(), &offset,
-                    bEarlyChange);
+    decoder->Decode(dest_buf_ptr, dest_size, &offset);
   } else {
     FlateUncompress(src_span, estimated_size, dest_buf, dest_size, &offset);
   }