Return the fanout histogram in a vector, not a map.

Change-Id: I742dcf882493f27ec3d35514bc8e9ff77b71686b
Reviewed-on: https://code-review.googlesource.com/c/re2/+/54334
Reviewed-by: Paul Wankadia <junyer@google.com>

re2/fuzzing/re2_fuzzer.cc

@@ -5,10 +5,10 @@
 #include <fuzzer/FuzzedDataProvider.h>
 #include <stddef.h>
 #include <stdint.h>
-#include <map>
 #include <memory>
 #include <queue>
 #include <string>
+#include <vector>
 
 #include "re2/prefilter.h"
 #include "re2/re2.h"
@@ -87,7 +87,7 @@ void TestOneInput(StringPiece pattern, const RE2::Options& options,
 
   // Don't waste time fuzzing high-fanout programs.
   // They can cause bug reports due to fuzzer timeouts.
-  std::map<int, int> histogram;
+  std::vector<int> histogram;
   int fanout = re.ProgramFanout(&histogram);
   if (fanout > 9)
     return;

re2/re2.cc

@@ -310,6 +310,40 @@ static int FindMSBSet(uint32_t n) {
 #endif
 }
 
+static int Fanout(Prog* prog, std::vector<int>* histogram) {
+  SparseArray<int> fanout(prog->size());
+  prog->Fanout(&fanout);
+  int data[32] = {};
+  int size = 0;
+  for (SparseArray<int>::iterator i = fanout.begin(); i != fanout.end(); ++i) {
+    if (i->value() == 0)
+      continue;
+    uint32_t value = i->value();
+    int bucket = FindMSBSet(value);
+    bucket += value & (value-1) ? 1 : 0;
+    ++data[bucket];
+    size = std::max(size, bucket+1);
+  }
+  if (histogram != NULL)
+    histogram->assign(data, data+size);
+  return size-1;
+}
+
+int RE2::ProgramFanout(std::vector<int>* histogram) const {
+  if (prog_ == NULL)
+    return -1;
+  return Fanout(prog_, histogram);
+}
+
+int RE2::ReverseProgramFanout(std::vector<int>* histogram) const {
+  if (prog_ == NULL)
+    return -1;
+  Prog* prog = ReverseProg();
+  if (prog == NULL)
+    return -1;
+  return Fanout(prog, histogram);
+}
+
 static int Fanout(Prog* prog, std::map<int, int>* histogram) {
   SparseArray<int> fanout(prog->size());
   prog->Fanout(&fanout);

re2/re2.h

@@ -195,6 +195,7 @@
 #include <map>
 #include <mutex>
 #include <string>
+#include <vector>
 
 #if defined(__APPLE__)
 #include <TargetConditionals.h>
@@ -291,7 +292,13 @@ class RE2 {
   int ProgramSize() const;
   int ReverseProgramSize() const;
 
-  // EXPERIMENTAL! SUBJECT TO CHANGE!
+  // If histogram is not null, outputs the program fanout
+  // as a histogram bucketed by powers of 2.
+  // Returns the number of the largest non-empty bucket.
+  int ProgramFanout(std::vector<int>* histogram) const;
+  int ReverseProgramFanout(std::vector<int>* histogram) const;
+
+  // DEPRECATED! WILL BE REMOVED!
   // Outputs the program fanout as a histogram bucketed by powers of 2.
   // Returns the number of the largest non-empty bucket.
   int ProgramFanout(std::map<int, int>* histogram) const;
@@ -630,8 +637,7 @@ class RE2 {
     Encoding encoding() const { return encoding_; }
     void set_encoding(Encoding encoding) { encoding_ = encoding; }
 
-    // Legacy interface to encoding.
-    // TODO(rsc): Remove once clients have been converted.
+    // DEPRECATED! WILL BE REMOVED!
     bool utf8() const { return encoding_ == EncodingUTF8; }
     void set_utf8(bool b) {
       if (b) {

re2/testing/re2_test.cc

@@ -12,6 +12,7 @@
 #include <map>
 #include <string>
 #include <utility>
+#include <vector>
 #if !defined(_MSC_VER) && !defined(__CYGWIN__) && !defined(__MINGW32__)
 #include <sys/mman.h>
 #include <unistd.h>  /* for sysconf */
@@ -473,7 +474,7 @@ TEST(ProgramFanout, BigProgram) {
   RE2 re100("(?:(?:(?:(?:(?:.)?){100})*)+)");
   RE2 re1000("(?:(?:(?:(?:(?:.)?){1000})*)+)");
 
-  std::map<int, int> histogram;
+  std::vector<int> histogram;
 
   // 3 is the largest non-empty bucket and has 1 element.
   ASSERT_EQ(3, re1.ProgramFanout(&histogram));