diff --git a/core/fxcodec/jbig2/jbig2_context.cpp b/core/fxcodec/jbig2/jbig2_context.cpp
index 219946e..a731247 100644
--- a/core/fxcodec/jbig2/jbig2_context.cpp
+++ b/core/fxcodec/jbig2/jbig2_context.cpp
@@ -18,6 +18,7 @@
 #include "core/fxcodec/jbig2/jbig2_grd_proc.h"
 #include "core/fxcodec/jbig2/jbig2_grrd_proc.h"
 #include "core/fxcodec/jbig2/jbig2_htrd_proc.h"
+#include "core/fxcodec/jbig2/jbig2_huffman_decoder.h"
 #include "core/fxcodec/jbig2/jbig2_pdd_proc.h"
 #include "core/fxcodec/jbig2/jbig2_sdd_proc.h"
 #include "core/fxcodec/jbig2/jbig2_trd_proc.h"
@@ -1212,49 +1213,31 @@
 
 std::vector<JBig2HuffmanCode> CJBig2_Context::DecodeSymbolIDHuffmanTable(
     uint32_t SBNUMSYMS) {
-  const size_t kRunCodesSize = 35;
-  std::array<JBig2HuffmanCode, kRunCodesSize> huffman_codes;
-  for (size_t i = 0; i < kRunCodesSize; ++i) {
-    if (stream_->readNBits(4, &huffman_codes[i].codelen) != 0) {
+  std::array<uint8_t, 35> runcode_lengths;
+  for (uint8_t& runcode_length : runcode_lengths) {
+    uint32_t code_length;
+    if (stream_->readNBits(4, &code_length) != 0) {
       return std::vector<JBig2HuffmanCode>();
     }
+    runcode_length = code_length;
   }
-  if (!HuffmanAssignCode(huffman_codes)) {
+
+  CJBig2_HuffmanTable runcode_table(runcode_lengths);
+  if (!runcode_table.IsOK()) {
     return std::vector<JBig2HuffmanCode>();
   }
 
+  CJBig2_HuffmanDecoder runcode_decoder(stream_.get());
+
   std::vector<JBig2HuffmanCode> SBSYMCODES(SBNUMSYMS);
   int32_t run = 0;
   int32_t i = 0;
   while (i < static_cast<int>(SBNUMSYMS)) {
-    size_t j;
-    FX_SAFE_INT32 nSafeVal = 0;
-    int32_t nBits = 0;
-    uint32_t nTemp;
-    while (true) {
-      if (stream_->read1Bit(&nTemp) != 0) {
-        return std::vector<JBig2HuffmanCode>();
-      }
-
-      nSafeVal <<= 1;
-      if (!nSafeVal.IsValid()) {
-        return std::vector<JBig2HuffmanCode>();
-      }
-
-      nSafeVal |= nTemp;
-      ++nBits;
-      const int32_t nVal = nSafeVal.ValueOrDie();
-      for (j = 0; j < kRunCodesSize; ++j) {
-        if (nBits == huffman_codes[j].codelen &&
-            nVal == huffman_codes[j].code) {
-          break;
-        }
-      }
-      if (j < kRunCodesSize) {
-        break;
-      }
+    int32_t runcode;
+    if (runcode_decoder.DecodeAValue(&runcode_table, &runcode) != 0) {
+      return std::vector<JBig2HuffmanCode>();
     }
-    int32_t runcode = static_cast<int32_t>(j);
+    uint32_t nTemp;
     if (runcode < 32) {
       SBSYMCODES[i].codelen = runcode;
       run = 0;
diff --git a/core/fxcodec/jbig2/jbig2_huffman_table.cpp b/core/fxcodec/jbig2/jbig2_huffman_table.cpp
index f040a09..2cdf63d 100644
--- a/core/fxcodec/jbig2/jbig2_huffman_table.cpp
+++ b/core/fxcodec/jbig2/jbig2_huffman_table.cpp
@@ -15,21 +15,9 @@
 #include "core/fxcrt/check.h"
 #include "core/fxcrt/check_op.h"
 #include "core/fxcrt/fx_safe_types.h"
-#include "core/fxcrt/raw_span.h"
 
 namespace {
 
-struct JBig2TableLine {
-  uint8_t PREFLEN;
-  uint8_t RANDELEN;
-  int32_t RANGELOW;
-};
-
-struct HuffmanTable {
-  bool HTOOB;
-  pdfium::raw_span<const JBig2TableLine> lines;
-};
-
 constexpr JBig2TableLine kTableLine1[] = {{1, 4, 0},
                                           {2, 8, 16},
                                           {3, 16, 272},
@@ -133,10 +121,7 @@
 }  // namespace
 
 CJBig2_HuffmanTable::CJBig2_HuffmanTable(size_t idx) {
-  const HuffmanTable& table = kHuffmanTables[idx];
-  HTOOB = table.HTOOB;
-  NTEMP = static_cast<uint32_t>(table.lines.size());
-  ok_ = ParseFromStandardTable(idx);
+  ok_ = ParseFromTable(kHuffmanTables[idx]);
   DCHECK(ok_);
 }
 
@@ -145,17 +130,33 @@
   ok_ = ParseFromCodedBuffer(pStream);
 }
 
+CJBig2_HuffmanTable::CJBig2_HuffmanTable(pdfium::span<uint8_t> prefix_lengths) {
+  std::vector<JBig2TableLine> lines(prefix_lengths.size() + 2);
+  for (size_t i = 0; const auto& length : prefix_lengths) {
+    lines[i].PREFLEN = length;
+    lines[i].RANGELEN = 0;
+    lines[i].RANGELOW = static_cast<int>(i);
+    ++i;
+  }
+  // Dummy open-ended intervals:
+  lines[prefix_lengths.size()] = {0, 0, 0};
+  lines[prefix_lengths.size() + 1] = {0, 0, 0};
+
+  ok_ = ParseFromTable({.HTOOB = false, .lines = lines});
+}
+
 CJBig2_HuffmanTable::~CJBig2_HuffmanTable() = default;
 
-bool CJBig2_HuffmanTable::ParseFromStandardTable(size_t idx) {
-  pdfium::span<const JBig2TableLine> lines =
-      kHuffmanTables[idx].lines.first(NTEMP);
+bool CJBig2_HuffmanTable::ParseFromTable(const HuffmanTable& table) {
+  HTOOB = table.HTOOB;
+  NTEMP = static_cast<uint32_t>(table.lines.size());
+  pdfium::span<const JBig2TableLine> lines = table.lines;
   CODES.resize(lines.size());
   RANGELEN.resize(lines.size());
   RANGELOW.resize(lines.size());
   for (size_t i = 0; const auto& line : lines) {
     CODES[i].codelen = line.PREFLEN;
-    RANGELEN[i] = line.RANDELEN;
+    RANGELEN[i] = line.RANGELEN;
     RANGELOW[i] = line.RANGELOW;
     ++i;
   }
diff --git a/core/fxcodec/jbig2/jbig2_huffman_table.h b/core/fxcodec/jbig2/jbig2_huffman_table.h
index 7f5d5a0..9a5723f 100644
--- a/core/fxcodec/jbig2/jbig2_huffman_table.h
+++ b/core/fxcodec/jbig2/jbig2_huffman_table.h
@@ -13,13 +13,35 @@
 #include <vector>
 
 #include "core/fxcodec/jbig2/jbig2_define.h"
+#include "core/fxcrt/raw_span.h"
 
 class CJBig2_BitStream;
 
+struct JBig2TableLine {
+  uint8_t PREFLEN;
+  uint8_t RANGELEN;
+  int32_t RANGELOW;
+};
+
+struct HuffmanTable {
+  bool HTOOB;
+
+  // If HTOOB is set: The last line is for the OOB symbol.
+  // Its RANGELEN and RANGELOW are ignored.
+  // The last two lines (before the OOB symbol line, if present)
+  // are for the -infinity...value range and the value...infinity range.
+  // If this table has no -infinity...value range, set its PREFLEN to 0.
+  pdfium::raw_span<const JBig2TableLine> lines;
+};
+
 class CJBig2_HuffmanTable {
  public:
   explicit CJBig2_HuffmanTable(size_t idx);
   explicit CJBig2_HuffmanTable(CJBig2_BitStream* pStream);
+
+  // Creates a huffman table that maps a canonical code with length
+  // prefix_lengths[i] to i.
+  explicit CJBig2_HuffmanTable(pdfium::span<uint8_t> prefix_lengths);
   ~CJBig2_HuffmanTable();
 
   bool IsHTOOB() const { return HTOOB; }
@@ -32,7 +54,7 @@
   static constexpr size_t kNumHuffmanTables = 16;
 
  private:
-  bool ParseFromStandardTable(size_t table_idx);
+  bool ParseFromTable(const HuffmanTable& table);
   bool ParseFromCodedBuffer(CJBig2_BitStream* pStream);
   void ExtendBuffers(bool increment);