[VCD] Do not emit the leading zeroes when writing a value change.

This helps to reduce the VCD files sizes.
ARM-software · Apr 25, 2024 · 736d872 · 736d872
1 parent 1918805
commit 736d872
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Showing 3 changed files with 69 additions and 15 deletions.
diff --git a/include/PAF/WAN/VCDWaveFile.h b/include/PAF/WAN/VCDWaveFile.h
@@ -30,25 +30,29 @@
 namespace PAF {
 namespace WAN {
 
-// The VCDWaveFile class is an abstraction of the VCD file format.
+/// The VCDWaveFile class is an abstraction of the VCD file format.
 class VCDWaveFile : public WaveFile {
   public:
     VCDWaveFile() = delete;
     VCDWaveFile(const VCDWaveFile &) = delete;
     VCDWaveFile(const std::string &filename)
         : WaveFile(filename, WaveFile::FileFormat::VCD) {}
 
-    // Convenience method to read from a single input file.
+    /// Convenience method to read from a single input file.
     Waveform read();
 
-    // Construct a Waveform from file FileName.
+    /// Construct a Waveform from file FileName.
     bool read(Waveform &W) override;
 
-    // Save Waveform W to file 'FileName'.
+    /// Save Waveform W to file 'FileName'.
     bool write(const Waveform &W) override;
 
-    // Quickly read the file to collect all times with changes.
+    /// Quickly read the file to collect all times with changes.
     std::vector<WAN::TimeTy> getAllChangesTimes() override;
+
+    /// Format the ValueChange string \p s for emitting in a VCD file by
+    /// stripping leading zeroes and lowercasing the string.
+    static std::string formatValueChange(const std::string &s);
 };
 
 } // namespace WAN

diff --git a/lib/WAN/VCDWaveFile.cpp b/lib/WAN/VCDWaveFile.cpp
@@ -782,14 +782,21 @@ struct VCDHierDumper : public Waveform::Visitor {
         o << " $end\n";
     }
 };
+} // namespace
+
+string VCDWaveFile::formatValueChange(const string &s) {
+    // Count leading zeroes
+    size_t leadingZeroes = 0;
+    while (s.size() - leadingZeroes > 1 && s[leadingZeroes] == '0')
+        leadingZeroes += 1;
 
-string to_lower(const string &s) {
-    string r(s);
-    std::transform(r.begin(), r.end(), r.begin(),
+    string r;
+    r.resize(s.size() - leadingZeroes);
+
+    std::transform(s.begin() + leadingZeroes, s.end(), r.begin(),
                    [](unsigned char c) { return std::tolower(c); });
     return r;
 }
-} // namespace
 
 bool VCDWaveFile::write(const Waveform &W) {
     std::ofstream F(fileName.c_str());
@@ -826,9 +833,10 @@ bool VCDWaveFile::write(const Waveform &W) {
                     DIE("VCD signal id not found");
                 size_t ChangeIdx = ChangeIndexes[Idx];
                 if (W[Idx].getNumBits() == 1)
-                    F << to_lower(W[Idx].getChange(ChangeIdx).value);
+                    F << formatValueChange(W[Idx].getChange(ChangeIdx).value);
                 else
-                    F << 'b' << to_lower(W[Idx].getChange(ChangeIdx).value)
+                    F << 'b'
+                      << formatValueChange(W[Idx].getChange(ChangeIdx).value)
                       << ' ';
                 F << r->second << '\n';
                 ChangeIndexes[Idx] += 1;
@@ -845,9 +853,12 @@ bool VCDWaveFile::write(const Waveform &W) {
                     if (r == VHD.sigMap.end())
                         DIE("VCD signal id not found");
                     if (W[Idx].getNumBits() == 1) {
-                        F << to_lower(W[Idx].getChange(ChangeIdx).value);
+                        F << formatValueChange(
+                            W[Idx].getChange(ChangeIdx).value);
                     } else {
-                        F << 'b' << to_lower(W[Idx].getChange(ChangeIdx).value)
+                        F << 'b'
+                          << formatValueChange(
+                                 W[Idx].getChange(ChangeIdx).value)
                           << ' ';
                     }
                     F << r->second << '\n';

diff --git a/unit-tests/VCDWaveFile.cpp b/unit-tests/VCDWaveFile.cpp
@@ -40,6 +40,36 @@ using namespace testing;
 
 static const string VCDInput(SAMPLES_SRC_DIR "Counters.vcd");
 
+TEST(VCDWaveFile, formatValueChange) {
+    EXPECT_EQ(VCDWaveFile::formatValueChange("0"), "0");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("1"), "1");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("A"), "a");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("a"), "a");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("F"), "f");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("f"), "f");
+
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00"), "0");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("01"), "1");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("0A"), "a");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("0a"), "a");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("0F"), "f");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("0f"), "f");
+
+    EXPECT_EQ(VCDWaveFile::formatValueChange("000"), "0");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("001"), "1");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00A"), "a");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00a"), "a");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00F"), "f");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00f"), "f");
+
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00100"), "100");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00201"), "201");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00a0A"), "a0a");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00e0a"), "e0a");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00F0F"), "f0f");
+    EXPECT_EQ(VCDWaveFile::formatValueChange("00c0f"), "c0f");
+}
+
 TEST(VCDWaveFile, Read) {
     VCDWaveFile F(VCDInput);
     EXPECT_EQ(F.getFileFormat(), WaveFile::FileFormat::VCD);
@@ -78,7 +108,10 @@ TEST_F(VCDWaveFileF, Write) {
         W.getRootScope()->addModule("instance", "test", "test");
     SignalIdxTy SIdx = W.addWire(S, "a_signal", 4);
     W.addValueChange(SIdx, 0, "0000");
+    W.addValueChange(SIdx, 5, string("0010"));
     W.addValueChange(SIdx, 10, string("1010"));
+    W.addValueChange(SIdx, 15, string("100"));
+    W.addValueChange(SIdx, 20, string("1"));
     F.write(W);
 
     EXPECT_TRUE(checkFileContent({
@@ -101,10 +134,16 @@ TEST_F(VCDWaveFileF, Write) {
     "$enddefinitions $end",
     "#0",
     "$dumpvars",
-    "b0000 !",
+    "b0 !",
     "$end",
+    "#5",
+    "b10 !",
     "#10",
-    "b1010 !"
+    "b1010 !",
+    "#15",
+    "b100 !",
+    "#20",
+    "b1 !"
     // clang-format off
   }));
 }